Mid Pleistocene 40-100 k.y. Glacial Cycle Transition Resolved

by Tommy on 27/10/2016

One less thing on my bucket list.



Breathing more deeply: Deep ocean carbon storage during the mid-Pleistocene climate transition, Caroline H. Lear, Katharina Billups, Rosalind E.M. Rickaby, Liselotte Diester-Haass, Elaine M. Mawbey and Sindia M. Sosdian, Geology, 44, 12, (20 October 2016), doi:10.1130/G38636.1

The ∼100 k.y. cyclicity of the late Pleistocene ice ages started during the mid-Pleistocene transition (MPT), as ice sheets became larger and persisted for longer. The climate system feedbacks responsible for introducing this nonlinear ice sheet response to orbital variations in insolation remain uncertain. Here we present benthic foraminiferal stable isotope (δ18O, δ13C) and trace metal records (Cd/Ca, B/Ca, U/Ca) from Deep Sea Drilling Project Site 607 in the North Atlantic. During the onset of the MPT, glacial-interglacial changes in δ13C values are associated with changes in nutrient content and carbonate saturation state, consistent with a change in water mass at our site from a nutrient-poor northern source during interglacial intervals to a nutrient-rich, corrosive southern source during glacial intervals. The respired carbon content of glacial Atlantic deep water increased across the MPT. Increased dominance of corrosive bottom waters during glacial intervals would have raised mean ocean alkalinity and lowered atmospheric pCO2. The amplitude of glacial-interglacial changes in δ13C increased across the MPT, but this was not mirrored by changes in nutrient content. We interpret this in terms of air-sea CO2 exchange effects, which changed the δ13C signature of dissolved inorganic carbon in the deep water mass source regions. Increased sea ice cover or ocean stratification during glacial times may have reduced CO2 outgassing in the Southern Ocean, providing an additional mechanism for reducing glacial atmospheric pCO2. Conversely, following the establishment of the ∼100 k.y. glacial cycles, δ13C of interglacial northern-sourced waters increased, perhaps reflecting reduced invasion of CO2 into the North Atlantic following the MPT.

And get this, it’s free, and on the internet!

I don’t even have to pound pavement.

Or travel to the Bahamas.

Or sleep in a bunk.

No Comments

Extraterrestrial Communications by Solar Spectral Modulation

by Tommy on 27/10/2016

This is not as crankish as it first appears.


Discovery of peculiar periodic spectral modulations in a small fraction of solar type stars,
E. F. Borra and E. Trottier (10 October 2016)

A Fourier transform analysis of 2.5 million spectra in the Sloan Digital Sky Survey was carried out to detect periodic spectral modulations. Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range. The signals cannot be caused by instrumental or data analysis effects because they are present in only a very small fraction of stars within a narrow spectral range and because signal to noise ratio considerations predict that the signal should mostly be detected in the brightest objects, while this is not the case. We consider several possibilities, such as rotational transitions in molecules, rapid pulsations, Fourier transform of spectral lines and signals generated by Extraterrestrial Intelligence (ETI). They cannot be generated by molecules or rapid pulsations. It is highly unlikely that they come from the Fourier transform of spectral lines because too many strong lines located at nearly periodic frequencies are needed. Finally we consider the possibility, predicted in a previous published paper, that the signals are caused by light pulses generated by Extraterrestrial Intelligence to makes us aware of their existence. We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centered near the spectral type of the sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work. Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.

Let me explain how this works. Assuming that humanity is able to subsequently and sequentially solve its reusable launch vehicle problems, space development and colonization problems, its global warming, ocean acidification carbon economy problems, its overpopulation problems, biodiversity loss problems and religious nuttery weaponization and nuclear weapons on ballistic missiles problems, and finally its asteroid tracking and deflection problems, then a sustainable solar system wide equilibrium civilization is inevitable. That means we’ll have a lot of time on our hands. What is a long lived humanoid civilization to do, besides being assimilated by the Borg?

Well, what we will do is build giant space based interferometer telescopes, where we will obtain extremely high resolution 3D holographic videos of nearby terrestrial planets and then we will spectrocopically analyze their emissions. Any other short or long live nearby civilizations will become immediately apparent. Absent axion based free energy and gravitational manipulation, the obvious thing to do is to attempt to communicate with these nearby long lived civilizations.

So here is the deal. Now that I have conclusively demonstrated that life is inevitable anywhere in this long lived stable universe where stable terrestrial planetary conditions exist (The Cosmic Evolution of Autobiogenesis), then I know that they are already observing us, they can see that we are developing technology, and thus they would already be signalling us. And the easiest way to do that reliably, is by Morse code, or some other spectral modulation of starlight. And given the distances involved and the angular dimensions required to build a modulator and/or emitter, the size and complexity of a deep space spectral modulator makes this an engineering exercise of relative simplicity. So as they say, that is that. Let humanity’s problem solving begin!

Oh … the humanity!

No Comments

Unparticles Revealed in the High Density Low Temperature Strongly Coupled Regime

by Tommy on 27/10/2016

There are two schools within the University of Illinois Urbana Champaign school of thought.

The Philip W. Phillips and the Robert G. Leigh/Taylor L. Hughes schools of thought.

Unparticles and D-Branes. I am leaning towards unparticles.

Strings and D-branes can’t be far behind.


Violation of f-sum Rule with Generalized Kinetic Energy, Kridsanaphong Limtragool and Philip W. Phillips (24 October 2016)

Motivated by the normal state of the cuprates in which the f-sum rule increases faster than a linear function of the particle density, we derive a conductivity sum rule for a system in which the kinetic energy operator in the Hamiltonian is a general function of the momentum squared. Such a kinetic energy arises in scale invariant theories and can be derived within the context of holography. Our derivation of the f-sum rule is based on the gauge couplings of a non-local Lagrangian in which the kinetic operator is a fractional Laplacian of order α. We find that the f-sum rule in this case deviates from the standard linear dependence on the particle density. We find two regimes. At high temperatures and low densities, the sum rule is proportional to nT(α−1)/αwhere T is the temperature. At low temperatures and high densities, the sum rule is proportional to n1+(2(α−1)/d) with d being the number of spatial dimensions. The result in the low temperature and high density limit, when α < 1, can be used to qualitatively explain the behavior of the effective number of charge carriers in the cuprates at various doping concentrations.

Unparticles! Whoever heard of such a thing.

No Comments

Mathematical and Physical Theory of Quantum Catastrophes

by Tommy on 27/10/2016

I studies René Thom extensively long ago, so this is particularly relevant to me.


Morphology of a quantum catastrophe, J. Mumford and D. H. J. O’Dell (25 October 2016)

Thom’s seven elementary catastrophes are the only structurally stable singularities in up to four dimensions (Thom 1975). Their stability against perturbations removes any symmetry requirement which accounts for their ubiquity in nature, e.g. – as caustics. Examples include rainbows (Nye 1999), the twinkling of starlight (Berry 1977), rogue waves at sea (Hohmann 2010) and structure formation in the universe (Zeldovich 1982). At large scales the intensity appears to diverge on a caustic, but at the scale of a wavelength interference smooths the singularity and produces characteristic diffraction patterns (Arnold 1975, Berry 1976, Trinkhaus 1977). At subwavelength scales wave catastrophes are organized by an underlying lattice of dislocations (nodes) around each of which the wave function circulates as a vortex (Pearcey 1946, Nye 1974). Here we study the morphology of a third generation beyond geometric and wave catastrophes, called quantum catastrophes, which are singularities of classical fields. They are regulated by quantizing the excitations, i.e. – second quantization (Leonhardt 2002, Berry 2004, Berry 2008, O’Dell 2012}, and live in Fock space which, being fundamentally discrete, leads to core-less discretized vortices. These are created or annihilated in pairs as the number of quanta is varied.

Fortunately last night’s ArXiv was far less breakthroughy than this stuff.

No Comments

High Pressure Superconductivity of BiTeI Verified

by Tommy on 27/10/2016

I’ve been watching this closely and it is moving along quickly.


Pressure-induced superconductivity in the giant Rashba system BiTeI, D. VanGennep, A. Linscheid, D. E. Jackson, S. T. Weir, Y. K. Vohra, H. Berger, G. R. Stewart, R. G. Hennig, P. J. Hirschfeld and J. J. Hamlin (25 October 2016)

At ambient pressure, BiTeI is the first material found to exhibit a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to ~ 40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with Tc values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute Tc and find that our data is consistent with phonon-mediated superconductivity.

So that, as they say, is that.

No Comments

Behavior of Dirac and Weyl Topological Semimetals Reviewed

by Tommy on 26/10/2016



Topological Semimetals, A.A. Burkov, Nature, 15, 1145 (25 October 2016)

Topological semimetals and metals have emerged as a new frontier in the field of quantum materials. Novel macroscopic quantum phenomena they exhibit are not only of fundamental interest, but may hold some potential for technological applications.

No Comments

Axion Crystals Proposed

by Tommy on 26/10/2016

It’s half a dozen super interesting papers a day now on the Arxiv. I predicted that.


Axion Crystals, Sho Ozaki and Naoki Yamamoto (25 October 2016)

The low-energy effective theories for gapped insulators are classified by three parameters: permittivity ϵ, permeability μ, and theta angle θ. Crystals with periodic ϵ are known as photonic crystals. We here study the band structure of photons in a new type of crystals with periodic θ (modulo 2π) in space, which we call the axion crystals. We find that the axion crystals have a number of new properties that the usual photonic crystals do not possess, such as the helicity-dependent photonic band gaps and the nonrelativistic gapless dispersion relation at small momentum. We briefly discuss possible realizations of axion crystals in condensed matter systems as well as high-energy physics.

No Comments

Dissipative Galaxy Halo Baryon Self Interactions Explains the Tully-Fisher Relation

by Tommy on 26/10/2016

The excitement over MOND theories was brief, apparently.


The Mass-Discrepancy Acceleration Relation: a Natural Outcome of Galaxy Formation in CDM halos, Aaron D. Ludlow, Alejandro Benitez-Llambay, Matthieu Schaller, Tom Theuns, Carlos S. Frenk, Richard Bower, Joop Schaye (Leiden), Robert A. Crain, Julio F. Navarro, Azadeh Fattahi and Kyle A. Oman (24 October 2016)

We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the EAGLE suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different subgrid models for stellar and AGN feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: different feedback processes — which produce different galaxy populations — mainly shift galaxies along the relation, rather than perpendicular to it. Furthermore, galaxies exhibit a single characteristic acceleration, g†, above which baryons dominate the mass budget, as observed. These observations have been hailed as evidence for modified Newtonian dynamics but can be accommodated within the standard cold dark matter paradigm.

See also: https://arxiv.org/abs/1610.06183

La Fin du MOND? Λ CDM is Fully Consistent with SPARC Acceleration Law, B.W. Keller and J.W. Wadsley, Submitted to ApJ Letters (19 October 2016)

Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond ΛCDM . In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 ΛCDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.

Forbes Starts with a Bang Article

You may now return to your task of looking for unusual low mass dark matter particles – axions.

There is still the dark energy controversy to chew on.

No Comments

Blue Phophorene Oxide as a Tunable Quantum Simulator Device

by Tommy on 25/10/2016



Blue Phosphorene Oxide: Strain-tunable Quantum Phase Transitions and Novel 2D Emergent Fermions, Liyan Zhu, Shan-Shan Wang, Shan Guan, Ying Liu, Tingting Zhang, Guibin Chen and Shengyuan A. Yang, Nano Lett, 16 (10), 6548-6554 (20 September 2016), DOI:10.1021/acs.nanolett.6b03208

Tunable quantum phase transitions and novel emergent fermions in solid state materials are fascinating subjects of research. Here, we propose a new stable two-dimensional (2D) material, the blue phosphorene oxide (BPO), which exhibits both. Based on first-principles calculations, we show that its equilibrium state is a narrow-bandgap semiconductor with three bands at low energy. Remarkably, a moderate strain can drive a semiconductor-to-semimetal quantum phase transition in BPO. At the critical transition point, the three bands cross at a single point at Fermi level, around which the quasiparticles are a novel type of 2D pseudospin-1 fermions. Going beyond the transition, the system becomes a symmetry-protected semimetal, for which the conduction and valence bands touch quadratically at a single Fermi point that is protected by symmetry, and the low-energy quasiparticles become another novel type of 2D double Weyl fermions. We construct effective models characterizing the phase transition and these novel emergent fermions, and we point out several exotic effects, including super Klein tunneling, supercollimation, and universal optical absorbance. Our result reveals BPO as an intriguing platform for the exploration of fundamental properties of quantum phase transitions and novel emergent fermions, and also suggests its great potential in nanoscale device applications.

No Comments

Transport Near a Quantum Critical Point Model Analyzed

by Tommy on 25/10/2016


Nonperturbative functional renormalization-group approach to transport in the vicinity of a (2+1)-dimensional O(N)-symmetric quantum critical point, Félix Rose and Nicolas Dupuis (20 October 2016)

Nonperturbative functional renormalization-group approach to transport in the vicinity of a (2+1)-dimensional O(N)-symmetric quantum critical point, Using a nonperturbative functional renormalization-group approach to the two-dimensional quantum O(N) model, we compute the low-frequency limit ω → 0 of the zero-temperature conductivity in the vicinity of the quantum critical point. Our results are obtained from a derivative expansion to second order of a scale-dependent effective action in the presence of an external (i.e., non-dynamical) non-Abelian gauge field. While in the disordered phase the conductivity tensor σ(ω) is diagonal, in the ordered phase it is defined, when N ≥ 3, by two independent elements, σA(ω) and σB(ω), respectively associated to SO(N) rotations which do and do not change the direction of the order parameter. For N = 2, the conductivity in the ordered phase reduces to a single component σA(ω). We show that limω→0σ(ω,δ)σA(ω,−δ)/σ2q is a universal number which we compute as a function of N (δ measures the distance to the quantum critical point, q is the charge and σq = q2/h the quantum of conductance). On the other hand we argue that the ratio σB(ω→0)/σq is universal in the whole ordered phase, independent of N and, when N → ∞, equal to the universal conductivity σq at the quantum critical point.

This presentation is theoretically, mathematically and computationally … expansive.

And I imagine … expensive.

See also: https://arxiv.org/abs/1507.02818


Critical region of the superfluid transition in the BCS-BEC crossover, T. Debelhoir and N. Dupuis, Phys. Rev. A 93, 023642 (24 February 2016), DOI:10.1103/PhysRevA.93.023642

We determine the size of the critical region of the superfluid transition in the BCS-BEC crossover of a three-dimensional fermion gas, using a renormalization-group approach to a bosonic theory of pairing fluctuations. For the unitary Fermi gas, we find a sizable critical region [TG,TG+], of order Tc, around the transition temperature Tc with a pronounced asymmetry: |TG+Tc| / |TGTc| ∼ 8. The critical region is strongly suppressed on the BCS side of the crossover but remains important on the BEC side.

No Comments

Structural Stability of Low Dimensional Materials Investigated

by Tommy on 25/10/2016


Existence Criterion of Low-Dimensional Materials, Jiapeng Chen, Biao Wang and Yangfan Hu (20 October 2016)

The discovery of graphene and other two-dimensional (2-D) materials has stimulated a general interest in low-dimensional (low-D) materials. Whereas long time ago, Peierls and Landau’s theoretical work had shown that any one- and two-dimensional materials could not exist in any temperature environment, the following two basic issues become the main concern for many researchers: why stable low-D materials can exist and what kind of low-D materials are stable. In this letter, we establish an energy stability criterion for low-D materials, which tries to provide a clear answer for these questions. We find that for any straight/planar low-D elemental materials, 1-D monatomic chains, 2-D honeycomb lattices, square lattices and triangular lattices are the only four permissible structures. For a specific kind of element, the stability of its low-D structure is determined by several derivatives of its interatomic potentials. We find that the stability of any straight/planar low-D structures can only be understood by assuming multi-body interatomic potentials. For reactive empirical bond-order (REBO) potential, the honeycomb structure is found to be the most stable one among all permissible planar 2-D structures. Using this criterion, the stable existence of graphene, silicene and germanene is explained.

Stability is easy to bork. Trust me on that.

No Comments

First Principles Calculation of the Thermal Conductivity of Solids

by Tommy on 25/10/2016


Ab initio Green-Kubo Approach for the Thermal Conductivity of Solids, Christian Carbogno, Rampi Ramprasad and Matthias Scheffler (20 October 2016)

We herein present a first-principles formulation of the Green-Kubo method that allows the accurate assessment of the non-radiative thermal conductivity of solid semiconductors and insulators in equilibrium ab initio molecular dynamics calculations. Using the virial for the nuclei, we propose a unique ab initio definition of the heat flux. Accurate size- and time convergence are achieved within moderate computational effort by a robust, asymptotically exact extrapolation scheme. We demonstrate the capabilities of the technique by investigating the thermal conductivity of extreme high and low heat conducting materials, namely diamond Si and tetragonal ZrO2.

No Comments

Electronic and Optical Correlations of Dense Excitons Probed

by Tommy on 22/10/2016

Last night’s ArXiv contained several landmark papers. Here’s one. Excitonic Mott transitions.



Negative activation energy and dielectric signatures of excitons and excitonic Mott transitions in quantum confined laser structures, Amit Bhunia, Kanika Bansal, Mohamed Henini, Marzook S. Alshammari and Shouvik Datta, Journal of Applied Physics, 120, 144304 (20 October 2016), DOI:10.1063/1.4964850

Mostly, optical spectroscopies are used to investigate the physics of excitons, whereas their electrical evidences are hardly explored. Here, we examined a forward bias activated differential capacitance response of GaInP-AlGaInP based multi-quantum well laser diodes to trace the presence of excitons using electrical measurements. Occurrence of negative activation energy after light emission is understood as thermodynamical signature of steady state excitonic population under intermediate range of carrier injections. Similar corroborative results are also observed in an InGaAs-GaAs quantum dot laser structure grown by molecular beam epitaxy. With increasing biases, the measured differential capacitance response slowly vanishes. This represents gradual Mott transition of an excitonic phase into an electron-hole plasma in a GaInP-AlGaInP laser diode. This is further substantiated by more and more exponentially looking shapes of high energy tails in electroluminescence spectra with increasing forward bias, which originates from a growing non-degenerate population of free electrons and holes. Such an experimental correlation between electrical and optical properties of excitons can be used to advance the next generation excitonic devices.

See also: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.155438

Observation of the exciton Mott transition in the photoluminescence of coupled quantum wells, Phys. Rev. B, 94, 155438 (21 October 2016)

Indirect excitons in coupled quantum wells have long radiative lifetimes and form a cold quasi-two-dimensional population suitable for studying collective quantum effects. Here we report the observation of the exciton Mott transition from an insulating (excitons) to a conducting (ionized electron-hole pairs) phase, which occurs gradually as a function of carrier density and temperature. The transition is inferred from spectral and time-resolved photoluminescence measurements around a carrier density of 2×1010cm−2 and temperatures of 12–16 K. An externally applied electric field is employed to tune the dynamics of the transition via the quantum-confined Stark effect. Our results provide evidence of a gradual nature of the exciton Mott transition.

They need to up the density.

Stay tuned. More to come.

No Comments

Five Dimensional Spacetime Appears in Topological Physics

by Tommy on 21/10/2016

This is another idea I’ve been fooling around with lately with respect to cosmogenesis.


Observation of a non-Abelian Yang Monopole: From New Chern Numbers to a Topological Transition, Seiji Sugawa, Francisco Salces-Carcoba, Abigail R. Perry, Yuchen Yue and Ian B. Spielman (19 October 2016)

Because global topological properties are robust against local perturbations, understanding and manipulating the topological properties of physical systems is essential in advancing quantum science and technology. For quantum computation, topologically protected qubit operations can increase computational robustness, and for metrology the quantized Hall effect directly defines the von Klitzing constant. Fundamentally, topological order is generated by singularities called topological defects in extended spaces, and is quantified in terms of Chern numbers, each of which measures different sorts of fields traversing surfaces enclosing these topological singularities. Here, inspired by high energy theories, we describe our synthesis and characterization of a singularity present in non-Abelian gauge theories – a Yang monopole – using atomic Bose-Einstein condensates in a five-dimensional space, and quantify the monopole in terms of Chern numbers measured on enclosing manifolds. While the well-known 1st Chern number vanished, the 2nd Chern number, measured for the first time in any physical settings, did not. By displacing the manifold, we then observed a phase transition from “topological” to “trivial” as the monopole left the manifold.

The general idea is that four dimensional space inflates in a time reversal invariant manner until the axion angle becomes infinitesimally small, and then the entire network of cosmic strings and domains start breaking up, and the particles and super axions are created, anti-annihilated, and the particles reheated in the resulting expanding four dimensional space time manifold. Since this process resembles an unzipping, the built in asymmetry results in the creation of matter.

In other words, matter over anti-matter is a result of the breaking of time reversal symmetry.

Regardless of my speculations and mathturbations, this is indeed a landmark paper.

No Comments

Cubic Diamond Hexagonal Lonsdaleite By Shock Compression

by Tommy on 21/10/2016

With this PETM result, even though the shards are largish, I was thinking about nanodiamods.


Nanosecond formation of diamond and lonsdaleite by shock compression of graphite, D. Kraus, A. Ravasio, M. Gauthier, D. O. Gericke, J. Vorberger, S. Frydrych, J. Helfrich, L. B. Fletcher, G. Schaumann, B. Nagler, B. Barbrel, B. Bachmann, E. J. Gamboa, S. Göde, E. Granados, G. Gregori, H. J. Lee, P. Neumayer, W. Schumaker, T. Döppner, R. W. Falcone, S. H. Glenzer and M. Roth, Nature Communications, 7, 10970 (14 March 2016), doi:10.1038/ncomms10970

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.

Lonsdaleite is a real survivor!

Update: I thought I had already covered this earlier when it was published, and I was right.

No Comments

Elon Musk and Tesla to Announce the Obvious Thing Tonight

by Tommy on 19/10/2016

The obvious thing being interfacing the car batteries with the house batteries.


And the house solar panels of course.

But I could be wrong.

Update: That feature seems more like a Solar City announcement, so with this announcement I’m going with integrated solar panels on the roof and the hood of the Tesla Model 3. Why not?

An obvious no brainer that should have been done decades ago to all conventional vehicles.

Update 2: Ok, ejection seats! That could work. Rockets have them, right?

Update 3: There does not seem to be any link to this.

Update 4: Self driving cars. I want flying cars!

And floating cities with moving sidewalks.

No Comments

Are Black Holes Preferentially Sucking in Dark Matter?

by Tommy on 19/10/2016
Cosmic Dark Matter Black Hole Baryon String Void Structure

Cosmic Dark Matter Black Hole Baryon String Void Structure

I have been entertaining lots of conceptual dark matter cosmic evolution scenarios lately.

This is just one of many. Lots O’fun it is.

But not very productive as of yet.

Too many possibilities.

So much spacetime.

No Comments

Pressure Induced Superconductivity of Bismuth Telluride Iodide BeTeI

by Tommy on 19/10/2016

I’ve been keeping an eye on this for a while.


Topological quantum phase transition and superconductivity induced by pressure in the bismuth tellurohalide BiTeI, Yanpeng Qi, Wujun Shi, Pavel G. Naumov, Nitesh Kumar, Raman Sankar, Walter Schnelle, Chandra Shekhar, F. C. Chou, Claudia Felser, Binghai Yan and Sergey A. Medvedev (17 October 2016)

A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor BiTeI with giant Rashba spin splitting. In this work, the evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr while the resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that the superconductivity may develop from the multi-valley semiconductor phase. The superconducting transition temperature Tc increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. Our results demonstrate that BiTeX (X = I, Br) compounds with non-trivial topology of electronic states display new ground states upon compression.

See also: https://arxiv.org/abs/1610.03983


Pressure dependence of the band-gap energy in BiTeI, Sümeyra Güler-Kılıç and Çetin Kılıç, Phys. Rev. B, 94, 165203 (13 October 2016), DOI:10.1103/PhysRevB.94.165203

The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated, at which BiTeI becomes a topological insulator. Comparison of the critical pressure to the pressure at which BiTeI undergoes a structural phase transition indicates that the closure of the band gap would not be hindered by a structural transformation. Moreover, the band-gap pressure coefficients of BiTeI are computed, and an expression of the critical pressure is devised in terms of these coefficients. Our findings indicate that the semilocal and dispersion-corrected approaches are in conflict about the compressibility of BiTeI, which result in overestimation and underestimation, respectively. Nevertheless, the effect of pressure on the atomic structure of BiTeI is found to be manifested primarily as the reduction of the width of the van der Waals gap according to both approaches, which also yield consistent predictions concerning the interlayer metallic bonding in BiTeI under compression. It is consequently shown that the calculated band-gap energies follow qualitatively and quantitatively the same trend within the two approximations employed here, and the transition to the zero-gap state occurs at the same critical width of the van der Waals gap.

This is more good evidence that we have a pretty good handle on these things by now.

No Comments

Tidal Disruption of Dark Matter Solves Missing Satellite Problem

by Tommy on 18/10/2016

This has also been out for a while. It’s still worth reading I guess. And it’s free!


Tidal stirring of satellites with shallow density profiles prevents them from being too big to fail, Mihai Tomozeiu, Lucio Mayer and Thomas Quinn, The Astrophysical Journal Letters, 827, 1 (5 August 2016), doi:10.3847/2041-8205/827/1/L15

The “too big to fail” problem is revisited by studying the tidal evolution of populations of dwarf satellites with different density profiles. The high-resolution cosmological ΛCDM “ErisMod” set of simulations is used. These simulations can model both the stellar and dark matter components of the satellites, and their evolution under the action of the tides of a Milky Way (MW)-sized host halo at a force resolution better than 10 pc. The stronger tidal mass loss and re-shaping of the mass distribution induced in satellites with γ = 0.6 dark matter density distributions, as those resulting from the effect of feedback in hydrodynamical simulations of dwarf galaxy formation, are sufficient to bring the circular velocity profiles in agreement with the kinematics of MW’s dSphs. In contrast, in simulations in which the satellites retain cusps at z = 0 there are several “massive failures” with circular velocities in excess of the observational constraints. Various sources of deviations in the conventionally adopted relation between the circular velocity at the half-light radius and the one-dimensional line of sight velocity dispersions are found. Such deviations are caused by the response of circular velocity profiles to tidal effects, which also varies depending on the initially assumed inner density profile and by the complexity of the stellar kinematics, which include residual rotation and anisotropy. In addition, tidal effects naturally induce large deviations in the stellar mass–halo mass relation for halo masses below 109 M, preventing any reliable application of the abundance matching technique to dwarf galaxy satellites.

American Astronomical Society Press Release

No Comments

A Virtual Zoo of Quantum Topological States of Exotic Matter

by Tommy on 18/10/2016

From the inventor of the subject.


Zoo of quantum-topological phases of matter, Xiao-Gang Wen (13 October 2016)

What are topological phases of matter? First, they are phases of matter at zero temperature. Second, they have a non-zero energy gap. Third, they are more complicated and subtle than the familiar gapped zero temperature phases, such as insulating and magnetic phases. This paper will give a simple introduction and a brief survey of topological phases of matter. We will first discuss topological phases that have topological order. Then we will cover topological phases that have no topological order.

Breakthrough prizes all around. Maybe he’s already got one. I haven’t bothered to look.

No Comments

Static Charge Density Waves Stripe Order Found in 1/8 LBCO

by Tommy on 18/10/2016

In other words, CDW order is either cooperative, or competitive, or both. I get that.

This has been out for a while, but now that it has a bona fide press release, it’s official!


Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4, X. M. Chen, V. Thampy, C. Mazzoli, A. M. Barbour, H. Miao, G. D. Gu, Y. Cao, J. M. Tranquada, M. P. M. Dean, and S. B. Wilkins, Phys. Rev. Lett. 117, 167001 (11 October 2016), doi:10.1103/PhysRevLett.117.167001

The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.875Ba0.125CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2¾  h. We discuss the implications of these results for some of the competing theories.

DOE/Brookhaven National Laboratory Press Release

No Comments

Ultra Cold Atoms Proposed as a Quantum Critical Simulator

by Tommy on 14/10/2016

Recall that Michael Kosterlitz, David Thouless and Duncan Haldane were recently awarded their Nobel Prizes in condensed matter physics. Recall also that I have recently proposed a bosonic superfluid dark matter and dark energy hypothesis, where the fundamental excitations of this bosonic quantum superfluid by high energy processes in ordinary and neutron stars, near black holes and other high density high energy exotic states of matter, connect the standard model to Einstein’s equation of gravitation and general relativity through ultra light super axions of some sort, in my rather lame and naive attempt to jump start a new quantum gravity and quantum cosmology unification. I have previously proposed that condensed matter and ultra cold atom trapping theories, experiments and numerical simulations are the ONLY way that we will be able to access this energy regime, and that already this has revolutionized our understanding of fundamental physics and its application to novel device physics. In fact, I have also already employed this strategy successfully on the origin of life problem. Therefore, I present here …


Quantitative Studies on the Quantum Critical Regime near Superfluid to Mott Insulator Transition, Hao Lee, Shiang Fang and Daw-Wei Wang (12 October 2016)

We investigate the critical behaviors of correlation length and critical exponents for strongly interacting bosons in a two-dimensional optical lattice via quantum Monte Carlo simulations. By comparing the full numerical results to those given by the effective theory, we quantitatively determine the critical regime where the universal scaling behaviors applies for both classical Berezinskii-Kosterlitz-Thouless transition at a finite temperature and quantum phase transition from superfluid to Mott insulator. Our results show that the critical regime can be as large as a few lattice sites in optical lattice and should be observable in present experimental conditions.

Quantum critical black hole collapse in on the horizon.

So is room temperature superconductivity.

I predict weirdness very soon now.

I could be wrong though.

No Comments

Gravitational Anomalies, Entanglement Entropy, Anomaly Inflow

by Tommy on 14/10/2016

This is another result from the University of Illinois – Urbana Champaign school of thought, that I have found to be extremely useful for my dark matter gravitational super duper axion hypothesis.



Entanglement Entropy & Anomaly Inflow, Taylor L. Hughes, Robert G. Leigh, Onkar Parrikar and Srinidhi T. Ramamurthy, Phys. Rev. D, 93, 065059 (30 March 2016)

We study entanglement entropy for parity-violating (time-reversal breaking) quantum field theories on R1,2 in the presence of a domain wall between two distinct parity-odd phases. The domain wall hosts a 1+1-dimensional conformal field theory (CFT) with non-trivial chiral central charge. Such a CFT possesses gravitational anomalies. It has been shown recently that, as a consequence, its intrinsic entanglement entropy is sensitive to Lorentz boosts around the entangling surface. Here, we show using various methods that the entanglement entropy of the three-dimensional bulk theory is also sensitive to such boosts owing to parity-violating effects, and that the bulk response to a Lorentz boost precisely cancels the contribution coming from the domain wall CFT. We argue that this can naturally be interpreted as entanglement inflow (i.e., inflow of entanglement entropy analogous to the familiar Callan-Harvey effect) between the bulk and the domain-wall, mediated by the low-lying states in the entanglement spectrum. These results can be generally applied to 2+1-d topological phases of matter that have edge theories with gravitational anomalies, and provide a precise connection between the gravitational anomaly of the physical edge theory and the low-lying spectrum of the entanglement Hamiltonian.

No Comments

Paleocene Eocene Thermal Maximum (PETM) Assigned to a Comet Impact

by Tommy on 14/10/2016


Impact ejecta at the Paleocene-Eocene boundary, Morgan F. Schaller, Megan K. Fung, James D. Wright, Miriam E. Katz and Dennis V. Kent, Science, 354, 6309, 225-229 (14 October 2016), DOI:10.1126/science.aaf5466

Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.

My interests in these kinds of subjects started slowly and developed over a long period of time. Originally it started back in 1989, on the day of the Loma Prieta earthquake that occurred on October 17th, 1989. I was actually working in a foramanifera laboratory at the Caribbean Marine Research Center CMRC at Lee Stocking Island in the Exuma Cays in the Bahamas at that time.

I wasn’t doing that kind of research, but I was interested in it since it was occurring all around me, and I suddenly found myself surrounded by geologists and biologists, subjects which I knew little or nothing about. And we had a tide gauge. And I had an island. So by then I was totally keyed into the tides.

So on that day I was desperately trying to get back to the states, trying to negotiate a ride on Mr. and Mrs. Perry’s private plane, with them, the owners of the island on which the research center was located, who did not particularly like me and viewed everything I did with suspicion. That’s another story entirely. I was bumped off the flight the previous week, and their private flight was my only option. So I went home to cool my jets, and on my way back down to the cay to catch that ride, as I was walking down the hill to the dock, I ran into the highest tide I have ever EVER witnessed in all the years I had spent in the Bahamas. It was truly an awesome tide, it covered up jagged coral rocks that had never been covered before, rocks that can rip the bottom out of your boat if you don’t see them. It was a totally off the scale high tide. It was the only subject of discussion when I arrived at the lab, and that tide alone prompted a complete rebuild of the tide gauge column, and eventually a shift to digital tide gauges. Eventually later that day I did get my ride back to West Palm Beach, with Mr. and Mrs. Perry, a very quiet and silent ride indeed, and as I finally arrived in Tampa on my connection, in the airport lobby I was presented with a major earthquake on all of the television screens. Ding! Tides cause earthquakes. I was hooked.

So once the internet arrived on the scene I was ready. It was something that I was watching constantly. So over Christmas vacation 2004 when I was watching the USGS earthquake map and when there I saw an 8.1 major earthquake in the deep southern ocean near the Macquarie Islands, I noticed. I thought to myself that something is on the move down there, and if there is one, there should be another, and so for the next few days I was watching that map like a hawk, and when it happened, I saw it. I was on it. The Boxing Day Indonesian earthquake and tsunami.

Massive Quake Strikes Remote Macquarie Island In Antarctica


I was posting on sci.earthquake at the time, and I wish now I had said something earlier, not just after the fact. I felt that way when I was sitting in Grandma’s chair watching the Columbia space shuttle launch on its final mission, when I saw something fall off the rocket and shred into the exhaust plumes of the solid rocket boosters. I was so concerned about it that I ran out into the back yard thinking I would catch the explosion, but there it was, cleanly accelerating over the horizon and into space. So I thought all is well, when in fact all was not well, and I regret to this day not relaying my observations and thoughts to the space cadet community on the usenet.

Between those two incidents and all of my experiences in search and rescue in the Bahamas – I decided right then and there, on Boxing Day in 2004, if I see something then I am reporting it.

At that point I was seeing a lot of things I did not like. It was in the middle of the Bush years. So when I noticed that Ellen Thomas was coming to Eckerd College in St. Petersburg to speak on global warming and the PETM on February 16th, 2005, I went down there to see her, and after the talk, I spoke with her. At that time comet impacts were considered fringe, but she gave me some pointers and again, I was hooked. Ellen Prager was my boss for a year in 1995 and so I was already a catastrophist. And of course, catastrophe was a daily occurrence at the research lab and in the islands. Crisis management and science and problem solving was my way of life.

So when the Younger Dryas impact hypothesis arrived on the scene, of course I was interested, and when on Darwin’s Day in 2009, when I saw something in the Black Sturgeon River Basin south of Lake Nipigon in Ontario, Canada, of course, I reported it. On Valentines Day. February 14, 2009. So even when I am wrong, and I am mostly wrong nowadays, I don’t regret reporting what I see. That’s my story and I’m sticking with it. Until I see that I am wrong. I am a scientist.

This is my microphone.

Update: The takeaway is that big impacts can cause earthquakes, tsunamis and volcanoes.

Supervolcanoes and volcanism is well known to release large amounts of carbon dioxide.

Positive feedbacks in these phenomena could well include large methane releases.

Instantaneous effects of an impact are followed by long term effects.

Therefore I consider this problem now to be solved.

Update 2: Wow, I just realized this is a five way super catastrophe.

Cosmic impact, massive earthquake swarm, giant tsunami, super volcanism and then when the coal beds burned up in that mess, global warming. Life is great, no? I’m a catastrophist!

No Comments

Trillions and Trillions

by Tommy on 14/10/2016
Hubble Trillions Of Galaxies

Hubble Trillions Of Galaxies


The Evolution of Galaxy Number Density at z < 8 and its Implications, Christopher J. Conselice, Aaron Wilkinson, Kenneth Duncan and Alice Mortlock, Accepted to ApJ (9 October 2016)

The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z ∼ 8 to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies (ϕT), more massive than M = 106 M, decreases as ϕTt−1, where t is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M > 107 M. By using the M = 106 M lower limit we further show that the total number of galaxies in the universe up to z = 8 is 2.0+0.7−0.6 × 1012 (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox.

Darkness seems to be winning in my universe.

And so I say – let there be light.

No Comments

Bismuth Topological Edge States Proposed for Thermoelectric ZT Efficiency Enhancements

by Tommy on 13/10/2016


Effects of topological edge states on the thermoelectric properties of Bi nanoribbons, L. Cheng, H. J. Liu, J. H. Liang, J. Zhang, J. Wei, P. H. Jiang and D. D. Fan (11 October 2016)

Using first-principles calculations combined with Boltzmann transport theory, we investigate the effects of topological edge states on the thermoelectric properties of Bi nanoribbons. It is found that there is a competition between the edge and bulk contributions to the Seebeck coefficients. However, the electronic transport of the system is dominated by the edge states because of its much larger electrical conductivity. As a consequence, a room temperature value exceeding 3.0 could be achieved for both p- and n-type systems when the relaxation time ratio between the edge and the bulk states is tuned to be 1000. Our theoretical study suggests that the utilization of topological edge states might be a promising approach to cross the threshold of the industrial application of thermoelectricity.

Eggimuffin. Yeah. Maybe.

No Comments

Time and Angle Resolved Photoemission Spectroscopy Probes Effects of Dirac Cone Warping on Transport and Structure of a Topological Superconductor – Bismuth Telluride – Bi2Te3

by Tommy on 12/10/2016



Observation of antiphase coherent phonons in the warped Dirac cone of Bi2Te3, E. Golias and J. Sánchez-Barriga, Phys. Rev. B 94, 161113R (11 October 2016), doi:PhysRevB.94.161113

In this Rapid Communication we investigate the coupling between excited electrons and phonons in the highly anisotropic electronic structure of the prototypical topological insulator Bi2Te3. Using time- and angle-resolved photoemission spectroscopy we are able to identify the emergence and ultrafast temporal evolution of the longitudinal-optical A1g coherent-phonon mode in Bi2Te3. We observe an antiphase behavior in the onset of the coherent-phonon oscillations between the ΓK¯ and the ΓM¯ high-symmetry directions that is consistent with warping. The qualitative agreement between our density-functional theory calculations and the experimental results reveals the critical role of the anisotropic coupling between Dirac fermions and phonon modes in the topological insulator Bi2Te3.

See also: Lightsources Article

Hot off the press.

Update: Bi2Te3 is actually the parent topological insulator of a topological superconductor.

No Comments

Bismuth Bi (111) and (110) Through Ultra Thin Nanowires

by Tommy on 12/10/2016


Electronic and structural properties of rhombohedral [111] and [110] oriented ultra-thin bismuth nanowires, Lida Ansari, Farzan Gity and James C. Greer (19 September 2016)

Structures and electronic properties of rhombohedral [111] and [110] bismuth nanowires are calculated with the use of density functional theory. The formation of an energy band gap from quantum confinement is studied and to improve estimates for the band gap the GW approximation is applied. The [111] oriented nanowires require surface bonds to be chemically saturated to avoid formation of metallic surface states whereas the surface of the [110] nanowires do not support metallic surface states. It is found that the onset of quantum confinement in the surface passivated [111] nanowires occurs at larger critical dimensions than for the [110] nanowires. For the [111] oriented nanowires it is predicted that a band gap of approximately 0.5 eV can be formed at a diameter of approximately 6 nm, whereas for the [110] oriented nanowires a diameter of approximately 3 nm is required to achieve a similar band gap energy. The GW correction is also applied to estimates of the electron affinity, ionisation potentials and work functions for both orientations of the nanowires for various diameters below 5 nm. The magnitude of the energy band gaps that arise in bismuth at critical dimensions of a few nanometers are of the same order as for conventional bulk semiconductors.

This is fairly brute force but the trends here are clearly distinguishable.

No Comments

Quantum Confinement Effect in Bismuth Multilayers Proposed for Conventional Electronics

by Tommy on 12/10/2016


Reinventing Solid State Electronics: Harnessing Quantum Confinement in Bismuth Thin Films, Farzan Gity, Lida Ansari, Martin Lanius, Peter Schüffelgen, Gregor Mussler, Detlev Grützmacher and James C. Greer (17 September 2016)

Solid state electronics relies on the intentional introduction of impurity atoms or dopants into a semiconductor crystal and/or the formation of junctions between different materials (heterojunctions) to create rectifiers, potential barriers, and conducting pathways. With these building blocks, switching and amplification of electrical currents and voltages is achieved. As miniaturization continues to ultra-scaled transistors with critical dimensions on the order of ten atomic lengths, the concept of doping to form rectifying junctions fails and heterojunction formation becomes extremely difficult. Here it is shown there is no need to introduce dopant atoms nor is the formation of a heterojunction required to achieve the fundamental electronic function of current rectification. Ideal diode behavior or rectification is achieved for the first time solely by manipulation of quantum confinement in approximately 2 nanometer thick films consisting of a single atomic element, the semimetal bismuth. Crucially for nanoelectronics, this new quantum approach enables room temperature operation.

I’m not exactly sure if diode electronics is the way to go with these things.

I have this terrible pain down my left side.

I’m feeling very depressed.

I might be paranoid.

I need positrons.

No Comments

New Detection Technique for Ultralight Dark Matter Axions

by Tommy on 11/10/2016

This is getting some press.



Broadband and Resonant Approaches to Axion Dark Matter Detection, Yonatan Kahn, Benjamin R. Safdi and Jesse Thaler, Phys. Rev. Lett. 117, 141801 (30 September 2016)

When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axionlike dark matter with masses in the range of 10−14 − 10−6 eV. In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant.

This closes the gap with ADMX.

No Comments

Berry Curvature Induction in Lattice QCD Simulations Revealed

by Tommy on 11/10/2016

This has been extremely helpful to my dark matter axion program.


Lattice QCD simulation of the Berry curvature, Arata Yamamoto, Talk Given at 34th Annual International Symposium on Lattice Field Theory – Lattice 2016 (7 October 2016)

The Berry curvature is a fundamental concept describing topological order of quantum systems. While it can be analytically tractable in non-interacting systems, numerical simulations are necessary in interacting systems. We present a formulation to calculate the Berry curvature in lattice QCD.

See also: https://arxiv.org/abs/1604.08424


Berry phase in lattice QCD, Arata Yamamoto, Phys. Rev. Lett. 117, 052001 (2016), DOI:10.1103/PhysRevLett.117.052001

We propose the lattice QCD calculation of the Berry phase which is defined by the ground state of a single fermion. We perform the ground-state projection of a single-fermion propagator, construct the Berry link variable on a momentum-space lattice, and calculate the Berry phase. As the first application, the first Chern number of the (2+1)-dimensional Wilson fermion is calculated by the Monte Carlo simulation.

No Comments

Current Induced Giant Diamagnetism in the Mott Insulator Calcium Ruthenate Ca2RuO4

by Tommy on 11/10/2016

When I see something this novel and interesting all I can do is repeat it verbatim.


Current Induced Giant Diamagnetism in the Mott Insulator Ca2RuO4, Chanchal Sow, Shingo Yonezawa, Sota Kitamura, Takashi Oka, Kazuhiko Kuroki, Fumihiko Nakamura and Yoshiteru Maeno (7 October 2016)

Mott insulators have surprised us many times by hosting new and diverse quantum phenomena when the frozen electrons are perturbed by various stimuli. Superconductivity, metal-insulator transition, and colossal magnetoresistance induced by element substitution, pressure, and magnetic field are prominent examples. Here we report a novel phenomenon, namely giant diamagnetism, in the Mott insulator Ca2RuO4 induced by electric current. With application of 1 A/cm2 current, the strongest diamagnetism among all nonsuperconducting materials is induced as the system is tuned to a semimetallic state. The origin lies in the emergence of indirect Dirac cones in the many-body spectrum and associated monopole-like anomaly in the momentum dependent susceptibility. This record-breaking and switchable diamagnetism is a new class of non-equilibrium quantum phenomena on the verge of Mott insulating states.

See also: https://arxiv.org/abs/1610.02854

Current Induced Giant Diamagnetism in the Mott Insulator Ca2RuO4, D. Sutter, C.G. Fatuzzo, S. Moser, M. Kim, R. Fittipaldi, A. Vecchione, V. Granata, Y. Sassa, F. Cossalter, G. Gatti, M. Grioni, H.M. Ronnow, N.C. Plumb, C.E. Matt, M. Shi, M. Hoesch, T.K. Kim, T.R. Chang, H.T. Jeng, C. Jozwiak, A. Bostwick, E. Rotenberg, A. Georges, T. Neupert and J. Chang (10 October 2016)

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realised in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide — using angle-resolved photoemission electron spectroscopy – the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund’s coupling J = 0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be important in explaining the nature of the insulating state. It is thus a combination of multiband physics, Coulomb interaction and Hund’s coupling that generates the Mott insulating state of Ca2RuO4. These results underscore the importance of Hund’s coupling in the ruthenates and related multiband materials.

I like where this is going.

No Comments

Electron Mass Enhanced Quantum Critical Material Proposed for Helium Free Cryogenic Refrigeration

by Tommy on 11/10/2016


Super-heavy electron material as metallic refrigerant for adiabatic demagnetization cooling, Yoshifumi Tokiwa, Boy Piening, Hirale S. Jeevan, Sergey L. Bud’ko, Paul C. Canfield and Philipp Gegenwart, Science Advances, 2, 9, e1600835 (9 September 2016), DOI:10.1126/sciadv.1600835

Low-temperature refrigeration is of crucial importance in fundamental research of condensed matter physics, because the investigations of fascinating quantum phenomena, such as superconductivity, superfluidity, and quantum criticality, often require refrigeration down to very low temperatures. Currently, cryogenic refrigerators with 3He gas are widely used for cooling below 1 K. However, usage of the gas has been increasingly difficult because of the current worldwide shortage. Therefore, it is important to consider alternative methods of refrigeration. We show that a new type of refrigerant, the super-heavy electron metal YbCo2Zn20, can be used for adiabatic demagnetization refrigeration, which does not require 3He gas. This method has a number of advantages, including much better metallic thermal conductivity compared to the conventional insulating refrigerants. We also demonstrate that the cooling performance is optimized in Yb1−xScxCo2Zn20 by partial Sc substitution, with x ~ 0.19. The substitution induces chemical pressure that drives the materials to a zero-field quantum critical point. This leads to an additional enhancement of the magnetocaloric effect in low fields and low temperatures, enabling final temperatures well below 100 mK. This performance has, up to now, been restricted to insulators. For nearly a century, the same principle of using local magnetic moments has been applied for adiabatic demagnetization cooling. This study opens new possibilities of using itinerant magnetic moments for cryogen-free refrigeration.

This is yet another step in the right direction.

No Comments

Bismuth Oxy Iodide (BiOI) Proposed as Efficient Excitonic Water Electrolysis Photocatalyst

by Tommy on 11/10/2016


Spatial separation of photo-generated electron-hole pairs in BiOBr/BiOI bilayer to facilitate water splittingSpatial separation of photo-generated electron-hole pairs in BiOBr/BiOI bilayer to facilitate water splitting, Zhen-Kun Tang, Wen-Jin Yin, Le Zhang, Bo Wen, Deng-Yu Zhang, Li-Min Liu and Woon-Ming Lau, Scientific Reports 6, 32764 (2 September 2016), doi:10.1038/srep32764

The electronic structures and photocatalytic properties of bismuth oxyhalide bilayers (BiOX1/BiOX2, X1 and X2 are Cl, Br, I) are studied by density functional theory. Briefly, their compositionally tunable bandgaps range from 1.85 to 3.41 eV, suitable for sun-light absorption, and all bilayers have band-alignments good for photocatalytic water-splitting. Among them, heterogeneous BiOBr/BiOI bilayer is the best as it has the smallest bandgap. More importantly, photo-excitation of BiOBr/BiOI leads to electron supply to the conduction band minimum with localized states belonging mainly to bismuth of BiOBr where the H+/H2 half-reaction of water-splitting can be sustained. Meanwhile, holes generated by such photo-excitation are mainly derived from the iodine states of BiOI in the valence band maximum; thus, the O2/H2O half-reaction of water splitting is facilitated on BiOI. Detailed band-structure analysis also indicates that this intriguing spatial separation of photo-generated electron-hole pairs and the two half-reactions of water splitting are good for a wide photo-excitation spectrum from 2–5 eV; as such, BiOBr/BiOI bilayer can be an efficient photocatalyst for water-splitting, particularly with further optimization of its optical absorptivity.

I have heard something like this before somewhere.

No Comments

Spin Orbit Coupling (SOC) Applied to the BCS-BEC Transition

by Tommy on 3/10/2016


BCS-BEC transition in a Dilute Bose Gas with Spin-Orbit Coupling, Dekun Luo, Rong Li and Lan Yin (30 September 2016)

We study a two-component Bose gas with a symmetric spin-orbit coupling, and find that two atoms can form a bound state with any intra- or inter-species scattering length. Consequently, in the dilute limit, a stable condensation of diatomic molecules in the Bardeen-Cooper-Shrieffer (BCS) pairing state can be formed with weakly-attractive inter-species and repulsive intra-species interactions. This BCS paring state is energetically favored over Bose-Einstein condensation (BEC) of atoms at low densities, but as the density increases, there is a first-order transition from the BCS to BEC states.

Cool. When can we start?

No Comments