Topological Quantum Physics Hits Precise Mathematical Order

by Tommy on 2/07/2015

A New Kind of Topological Quantum Order: A Dimensional Hierarchy of Quasiparticles Built from Stationary Excitations, Sagar Vijay, Jeongwan Haah and Liang Fu

We introduce exactly solvable models of interacting (Majorana) fermions in d ≥ 3 spatial dimensions that realize a new kind of topological quantum order, building on a model presented in ref. [1]. These models have extensive topological ground-state degeneracy and a hierarchy of point-like, topological excitations that are only free to move within sub-manifolds of the lattice. In particular, one of our models has fundamental excitations that are completely stationary. To demonstrate these results, we introduce a powerful polynomial representation of commuting Majorana Hamiltonians. Remarkably, the physical properties of the topologically-ordered state are encoded in an algebraic variety, defined by the common zeros of a set of polynomials over a finite field. This provides a “geometric” framework for the emergence of topological order.

See also [Ref. 1]:

Majorana Fermion Surface Code for Universal Quantum Computation, Sagar Vijay, Timothy H. Hsieh and Liang Fu

We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of phase-locked s-wave superconducting islands on a topological insulator surface. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.

I finally got around to reading these on my vacation.

I am now officially freaked out.

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Bernie Sanders For President – Rock Concert at the Coliseum

by Tommy on 2/07/2015
Bernie Sanders For Preside - Madison Wisconsin - Coliseum

Bernie Sanders For President – Madison Wisconsin – Coliseum

Those were the days. I wonder what he thinks of space?

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Iron Impurities in Iron Chalcogenide Superconductors Fe(Te,Se) Reveal the Presence of Majorana Bound States

by Tommy on 2/07/2015

Observation of a robust zero-energy bound state in iron-based superconductor Fe(Te,Se), J-X. Yin, Zheng Wu, J-H. Wang, Z-Y. Ye, Jing Gong, X-Y. Hou, Lei Shan, Ang Li, X-J. Liang, X-X. Wu, Jian Li, C-S. Ting, Z-Q. Wang, J-P. Hu, P-H. Hor, H. Ding and S. H. Pan, Nature Physics, 11, 543–546 (22 June 2015), doi:10.1038/nphys3371

In superconductors, electrons are paired and condensed into the ground state. An impurity can break the electron pairs into quasiparticles with energy states inside the superconducting gap. The characteristics of such in-gap states reflect accordingly the properties of the superconducting ground state. A zero-energy in-gap state is particularly noteworthy, because it can be the consequence of non-trivial pairing symmetry or topology. Here we use scanning tunnelling microscopy/spectroscopy to demonstrate that an isotropic zero-energy bound state with a decay length of ~10 Å emerges at each interstitial iron impurity in superconducting Fe(Te,Se). More noticeably, this zero-energy bound state is robust against a magnetic field up to 8 T, as well as perturbations by neighbouring impurities. Such a spectroscopic feature has no natural explanation in terms of impurity states in superconductors with s-wave symmetry, but bears all the characteristics of the Majorana bound state proposed for topological superconductors, indicating that the superconducting state and the scattering mechanism of the interstitial iron impurities in Fe(Te,Se) are highly unconventional.

It’s official. The long awaited revolution has finally arrived.

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Macroscopic Quantum Phase Coherence Coherent Caloritronics

by Tommy on 2/07/2015

Nanoscale phase-engineering of thermal transport with a Josephson heat modulator, Nanoscale phase-engineering of thermal transport with a Josephson heat modulator, Antonio Fornieri, Christophe Blanc, Riccardo Bosisio, Sophie D’Ambrosio and Francesco Giazotto

Macroscopic quantum phase coherence has one of its pivotal expressions in the Josephson effect, which manifests itself both in charge and energy transport. The ability to master the amount of heat transferred through two tunnel-coupled superconductors by tuning their phase difference is the core of coherent caloritronics, and is expected to be a key tool in a number of nanoscience fields, including solid state cooling, thermal isolation, radiation detection, quantum information and thermal logic. Here we show the realization of the first balanced Josephson heat modulator designed to offer full control at the nanoscale over the phase-coherent component of thermal currents. Our device provides magnetic-flux-dependent temperature modulations up to 40 mK in amplitude with a maximum of the flux-to-temperature transfer coefficient reaching 200 mK per flux quantum at a bath temperature of 25 mK. Foremost, it demonstrates the exact correspondence in the phase-engineering of charge and heat currents, breaking ground for advanced caloritronic nanodevices such as thermal splitters, heat pumps and time-dependent electronic engines.

Who did not see this coming?

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Paragon Space Development Prefers CELSS over CELLS

by Tommy on 1/07/2015

CNN Paragon Mars One Article

Paragon Space Development Corporation Mars One CELSS PDF

I do not want to be the one keeping all that hardware running smoothly.

I have a completely different approach. CELLS – Closed Ecological Living and Life Support.

GroX – The Grok Box Grow Box System

GroX Grok Box Website

This has the added advantage that all that polyethylene and polypropylene will make excellent cosmic and solar radiation shielding on the nine month trip to Mars. I was supposed to write this up for NASA and Innocentive by July 6th, but I’m fed up with it. 15K for 100K worth of work? Meh.

By the time these guys get to Mars, solid state and condensed matter physics will have easily achieved the revolutionary advances necessary to completely obsolete this kind of approach.

Thomas Lee Elifritz – Biography

Previous Post on this subject.

If I go to Mars, it will be to retire and chill, not work.

Ceres is where I want to be.

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Edge Mode Superconductivity in a 2D Topological Insulator

by Tommy on 1/07/2015

Edge-mode superconductivity in a two-dimensional topological insulator, Vlad S. Pribiag, Arjan J. A. Beukman, Fanming Qu, Maja C. Cassidy, Christophe Charpentier, Werner Wegscheider and Leo P. Kouwenhoven, Nature Nanotechnology (11 May 2015), doi:10.1038/nnano.2015.86

Topological superconductivity is an exotic state of matter that supports Majorana zero-modes, which have been predicted to occur in the surface states of three-dimensional systems, in the edge states of two-dimensional systems, and in one-dimensional wires. Localized Majorana zero-modes obey non-Abelian exchange statistics, making them interesting building blocks for topological quantum computing. Here, we report superconductivity induced in the edge modes of semiconducting InAs/GaSb quantum wells, a two-dimensional topological insulator. Using superconducting quantum interference we demonstrate gate-tuning between edge-dominated and bulk-dominated regimes of superconducting transport. The edge-dominated regime arises only under conditions of high-bulk resistivity, which we associate with the two-dimensional topological phase. These experiments establish InAs/GaSb as a promising platform for the confinement of Majoranas into localized states, enabling future investigations of non-Abelian statistics.

Update: Here is the published PDF.

See also:

Topological Superconductivity – Edging Closer, Luke Fleet, Nature Physics, 11, 523 (1 July 2015), doi:10.1038/nphys3399

There are three types of fermions in condensed-matter systems: Dirac, Weyl and Majorana. Whereas Dirac fermions are now commonplace thanks to graphene, and experimental evidence for Weyl fermions is growing stronger, Majorana fermions currently remain as elusive as Ettore Majorana himself. Topological superconductors are predicted to host…

Vlad et al. have been working on this for a while. I just noticed he downloaded my essay.

I also just noticed I forgot the st in 21st Century. How embarrassing, lol.

Six months and I never saw it. Proof reading is a science.

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Ceres Crater Bright Spot is a Crack that is Spewing Water Ice

by Tommy on 30/06/2015

Cryovolcanism and/or geysers and water ice is now the leading candidate hypothesis.

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Niobium Phosphide NbP – Extreme Magnetoresistence and Ultrahigh Relativistic Electron Mobility in a Weyl Semimental

by Tommy on 30/06/2015

Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP, Chandra Shekhar, Ajaya K. Nayak, Yan Sun, Marcus Schmidt, Michael Nicklas, Inge Leermakers, Uli Zeitler, Yurii Skourski, Jochen Wosnitza, Zhongkai Liu, Yulin Chen, Walter Schnelle, Horst Borrmann, Yuri Grin, Claudia Felser and Binghai Yan, Nature Physics (22 June 2015), doi:10.1038/nphys3372

Recent experiments have revealed spectacular transport properties in semimetals, such as the large, non-saturating magnetoresistance exhibited by WTe2 (ref. 1). Topological semimetals with massless relativistic electrons have also been predicted as three-dimensional analogues of graphene. These systems are known as Weyl semimetals, and are predicted to have a range of exotic transport properties and surface states, distinct from those of topological insulators. Here we examine the magneto-transport properties of NbP, a material the band structure of which has been predicted to combine the hallmarks of a Weyl semimetal, with those of a normal semimetal. We observe an extremely large magnetoresistance of 850,000% at 1.85 K (250% at room temperature) in a magnetic field of up to 9 T, without any signs of saturation, and an ultrahigh carrier mobility of 5 × 106 cm2 V−1 s−1 that accompanied by strong Shubnikov–de Haas (SdH) oscillations. NbP therefore presents a unique example of a material combining topological and conventional electronic phases, with intriguing physical properties resulting from their interplay.

See also:

An inversion breaking Weyl semimetal state in the TaAs material class, Shin-Ming Huang, Su-Yang Xu, Ilya Belopolski, Chi-Cheng Lee, Guoqing Chang, BaoKai Wang, Nasser Alidoust, Guang Bian, Madhab Neupane, Arun Bansil, Hsin Lin and M. Zahid Hasan, Nature Commun. 6, 7373 (12 June 2015), doi:10.1038/ncomms8373

The recent discoveries of Dirac fermions in graphene and on the surface of topological insulators have ignited worldwide interest in physics and materials science. A Weyl semimetal is an unusual crystal where electrons also behave as massless quasi-particles but interestingly they are not Dirac fermions. These massless particles, Weyl fermions, were originally considered in massless quantum electrodynamics but have not been observed as a fundamental particle in nature. A Weyl semimetal provides a condensed matter realization of Weyl fermions, leading to unique transport properties with novel device applications. Such a semimetal is also a topologically non-trivial metallic phase of matter extending the classification of topological phases beyond insulators. The signature of a Weyl semimetal in real materials is the existence of unusual Fermi arc surface states, which can be viewed as half of a surface Dirac cone in a topological insulator. Here, we identify the first Weyl semimetal in a class of stoichiometric materials, which break crystalline inversion symmetry, including TaAs, TaP, NbAs and NbP. Our first-principles calculations on TaAs reveal the spin-polarized Weyl cones and Fermi arc surface states in this compound. We also observe pairs of Weyl points with the same chiral charge which project onto the same point in the surface Brillouin zone, giving rise to multiple Fermi arcs connecting to a given Weyl point. Our results show that TaAs is the first topological semimetal identified which does not depend on fine-tuning of chemical composition or magnetic order, greatly facilitating an exploration of Weyl physics in real materials.

Published as: A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class, Shin-Ming Huang, Su-Yang Xu, Ilya Belopolski, Chi-Cheng Lee, Guoqing Chang, BaoKai Wang, Nasser Alidoust, Guang Bian, Madhab Neupane, Chenglong Zhang, Shuang Jia, Arun Bansil, Hsin Lin and M. Zahid Hasan, Nature Commun. 6, 7373 (12 June 2015), doi:10.1038/ncomms8373

Weyl fermions are massless chiral fermions that play an important role in quantum field theory but have never been observed as fundamental particles. A Weyl semimetal is an unusual crystal that hosts Weyl fermions as quasiparticle excitations and features Fermi arcs on its surface. Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators. Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class. Our first-principles calculations on TaAs reveal its bulk Weyl fermion cones and surface Fermi arcs. Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

The phosphides and Group Vs have finally arrived, apparently. Better late than never.

‘Extreme’ and ‘ultra’ are new the new condensed matter physics catchwords.

Phosphine and bismuthine under pressure are suddenly looking good.

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A Bad Day in Launch Control For SpaceX and the United States

by Tommy on 28/06/2015

The loss of coffee for the Gemini 7 espresso machine is going to be almost unbearable.

Condolences all around. Shit happens. Usually at the worst possible time.

Chemical reaction engines (aka rockets) are like that.

The reactions should be interesting.

Update: After thinking this over my first wild uninformed speculative guess is moisture and ice. I’m in Florida now and it has been ridiculously hot, moist and wet here and we’re at the height of summer. It wouldn’t take much – minor oversight in air conditioning or exposure in some valves.

Update 2: It’s looking more like structural failure in the upper stage oxygen tank dome area. Defect or deformation in manufacturing or payload mating procedures. But it could be anything.

Gary Hudson has an interesting hypothesis that tracks back to the helium pressurization system, making the dome failure a symptom rather than the cause, and so it still could be something as simple as moisture. There is a known history of helium pressurization problems.

Update 3: Another hypothesis being put forth is related to a dynamic resonant instability of a 500 kilogram docking adapter payload slightly stressing the upper stage oxygen dome welds. This is a three point suspension arrangement in the Dragon trunk that may have been vibrating.

I can see how the non-intuitiveness of all this is going to take some time to sort out. Since there was an over pressure event, the pressurization system seems to be at fault, but one has to sort out the cascading avalanche of symptoms from the disease. Is there a doctor in the house?

Oh well. VEGGIE units to the rescue!

Eat healthy. Get smart.

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Cosmic Weather Report – Absolutely Perfectly Crystal Clear

by Tommy on 27/06/2015
Of Course I Still Love You

Of Course I Still Love You

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Bismuth Adatoms on Graphene on Silicon Carbide Reported

by Tommy on 27/06/2015

Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene, H.-H. Chen, S. H. Su, S.-L. Chang, B.-Y. Cheng, S. W. Chen, H.-Y. Chen, M.-F. Lin and J. C. A. Huang, Scientific Reports, 5, 11623 (23 June 2015), doi:10.1038/srep11623

To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~ 500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

First of all, this is just another reporting of a previous result published in Carbon. Same results, same authors, different journal. At least this report is open and includes some more information.

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SpaceX and Blue Origin Call For New Reusable Cryogenic Engines, Propulsion and Launch Vehicle Development

by Tommy on 27/06/2015

Congressional Testimony of Jeffrey Thornburg – SpaceX.

An alternative approach, and consistent with the U.S. Air Force’s current planning, SpaceX recommends that Congress allow for a broader set of investments into propulsion technologies, prototypes, test infrastructure, and advanced systems in order to enhance the U.S. liquid propulsion industrial base more broadly than an effort to fund a single engine (with potentially retrograde technology) would ever do.

Congressional Testimony of Robert Meyerson – Blue Origin

The U.S. industrial base now includes a number of commercial companies, like Blue Origin, that have developed significant liquid propulsion capabilities with private investment. We’re spending our own money, rather than taxpayer’s funds, and we are taking a “clean sheet” approach to development. We have invested in modern manufacturing equipment and processes to maximize production efficiency. We aren’t burdened by unused capacity that so often gets billed back to the Government in the form of high overhead rates. As a result, we are able to out compete the Russians, building modern, American engines on flexible production lines to serve multiple launch vehicles.

Is there another billionaire with an ego in the house?

My money’s on the kid with the rocket.

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Antonin Scalia Says – Keep Off My Lawn You Dirty Hippie

by Tommy on 26/06/2015
Don't Step On My Lawn You Dirty Hippie

Don’t Step On My Lawn You Dirty Hippie

Excuse me, Sir, I’m so sorry. Please accept my sincerest apologies.

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Laurentide Ice Sheet Esker Formation and Subglacial Drainage

by Tommy on 26/06/2015

An ice-sheet scale comparison of eskers with modelled subglacial drainage routes, Stephen J. Livingstone, Robert D. Storrar, John K. Hillier, Chris R. Stokes, Chris D. Clark and Lev Tarasov, Geomorphology, 246, 104–112 (1 October 2015), doi:10.1016/j.geomorph.2015.06.016

Eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage. In this paper, we compare the spatial pattern of eskers beneath the former Laurentide Ice Sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice-sheet model. Perhaps surprisingly, we show that eskers predominantly occur in regions where modelled subglacial water flow is low. Eskers and modelled subglacial drainage routes were found to typically match over distances of < 10 km, and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation. This supports a time-transgressive esker pattern, with formation in short (< 10 km) segments of conduit close behind a retreating ice margin, and probably associated with thin, stagnant or sluggish ice. Esker-forming conduits were probably dominated by supraglacially fed meltwater inputs. We also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo-ice stream locations. The paucity of eskers along the terrestrial portion of these palaeo-ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast-flowing ice.

Open Access Funded by the Natural Environment Research Council in the United Kingdom.

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Quantum Light Proposed For Ultracold Atomic Gases

by Tommy on 26/06/2015

Probing and Manipulating Fermionic and Bosonic Quantum Gases with Quantum Light
Thomas J. Elliott, Gabriel Mazzucchi, Wojciech Kozlowski, Santiago F. Caballero-Benitez and Igor B. Mekhov

We study the atom-light interaction in the fully quantum regime, with focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyze the entanglement between light and matter and show how it can be exploited for realizing multimode macroscopic quantum superpositions such as Schrödinger cat states, for both bosons and fermions. We provide examples utilizing different measurement schemes, and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases, and significantly altering the phase diagram of the atomic system.

Wow. Just wow.

In summary, we have shown how to use light scattering from ultracold atoms to perform QND measurements on fermionic systems, and demonstrated how the quantum addition to the classical diffraction pattern carries information about quantum correlations of the atomic state. Focusing on a single experimental run, we discussed the entanglement properties between light and matter and showed how these can be exploited for creating macroscopic quantum superpositions with fermionic and bosonic systems. We provided different schemes for the realization of such states and suggested how to make them more robust to decoherence by using a homodyne measurement. Finally, we described the phase diagram of a system of bosons in an optical cavity trapped in an optical lattice. The cavity mediates an effective long-range interaction which stabilizes a superfluid state with minimal fluctuations and suppresses the Mott insulator states.

I will donate my cat if it will help.

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Of Course I Still Love You More Than Coffee

by Tommy on 25/06/2015
Of Course I Still Love You - SpaceX Drone Ship - ASDS

Of Course I Still Love You – SpaceX Drone Ship – ASDS

But don’t make me prove it … again.

Photo: Ben Cooper/SpaceX.

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Dramatically Improved Spin Polarimeter Tested on Bismuth (111)

by Tommy on 25/06/2015

Multi-channel exchange-scattering spin polarimetry, Fuhao Ji, Tan Shi, Mao Ye, Weishi Wan, Zhen Liu, Jiajia Wang, Tao Xu and Shan Qiao

Electron spin takes critical role in almost all novel phenomena discovered in modern condensed matter physics (High-temperature superconductivity, Kondo effect, Giant Magnetoresistance, topological insulator, quantum anomalous Hall effect, etc.). However, the measurements for electron spin is of poor quality which blocks the development of material sciences because of the low efficiency of spin polarimeter. Here we show an imaging type exchange-scattering spin polarimeter with 5 orders more efficiency compared with a classical Mott polarimeter. As a demonstration, the fine spin structure of electronic states in bismuth (111) is investigated, showing the strong Rashba type spin splitting behavior in both bulk and surface states. This improvement pave the way to study novel spin related phenomena with unprecedented accuracy.

All Hail The Probe!

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30 nm Bismuth Bi (111) Films on Bi2Te3 Substrate Investigated

by Tommy on 19/06/2015

Topologically Nontrivial Bismuth(111) Thin Films Grown on Bi2Te3, Meng-Yu Yao, Fengfeng Zhu, Lin Miao, C. Q. Han, Fang Yang, D. D. Guan, C. L. Gao, Canhua Liu, Dong Qian and Jin-feng Jia

Using high-resolution angle-resolved photoemission spectroscopy, the electronic structure near the Fermi level and the topological property of the Bi(111) films grown on the Bi2Te3(111) substrate were studied. Very different from the bulk Bi, we found another surface band near the M¯ point besides the two well-known surface bands on the Bi(111) surface. With this new surface band, the bulk valence band and the bulk conduction band of Bi can be connected by the surface states. Our band mapping revealed odd number of Fermi crossings of the surface bands, which provided a direct experimental signature that Bi(111) thin films of a certain thickness on the Bi2Te3(111) substrate can be topologically nontrivial in three dimensions.

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Insulators Superconductors Related by Duality Transformations

by Tommy on 19/06/2015

Equivalence of Topological Insulators and Superconductors, E. Cobanera and G. Ortiz

Systems of free fermions are classified by symmetry, space dimensionality, and topological properties described by K-homology. Those systems belonging to different classes are inequivalent. In contrast, we show that by taking a many-body/Fock space viewpoint it becomes possible to establish equivalences of topological insulators and superconductors in terms of duality transformations. These mappings connect topologically inequivalent systems of fermions, jumping across entries in existent classification tables, because of the phenomenon of symmetry transmutation by which a symmetry and its dual partner have identical algebraic properties but very different physical interpretations. To constrain our study to established classification tables, we define and characterize mathematically Gaussian dualities as dualities mapping free fermions to free fermions (and interacting to interacting). By introducing a large, flexible class of Gaussian dualities we show that any insulator is dual to a superconductor, and that fermionic edge modes are dual to Majorana edge modes, that is, the Gaussian dualities of this paper preserve the bulk-boundary correspondence. Transmutation of relevant symmetries, particle number, translation, and time reversal is also investigated in detail. As illustrative examples, we show the duality equivalence of the dimerized Peierls chain and the Majorana chain of Kitaev, and a two-dimensional Kekule’ – type topological insulator, including graphene as a special instance in coupling space, dual to a p-wave superconductor. Since our analysis extends to interacting fermion systems we also briefly discuss some such applications.

This is the latest from a series of results that are going to have a major impact on things.

Stuff. It’s the new thing.

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President Obama Responds to Pope’s Environmental Encyclical

by Tommy on 19/06/2015

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Iron Chalcogenide Superconductors Are Strongly Correlated

by Tommy on 15/06/2015

Observation of universal strong orbital-dependent correlation effects in iron chalcogenides
Ming Yi, Zhongkai Liu, Yan Zhang, Rong Yu, Jianxin Zhu, James Lee, Rob Moore, Felix Schmitt, Wei Li, Scott Riggs, Jiun-Haw Chu, Bing Lv, Jin Hu, Makoto Hashimoto, Sung-Kwan Mo, Zahid Hussain, Zhiqiang Mao, Ching-Wu Chu, Ian Fisher, Qimiao Si, Zhi-Xun Shen and Donghui Lu, Submitted to Nature Communications

Establishing the appropriate theoretical framework for unconventional superconductivity in the iron-based materials requires correct understanding of both the electron correlation strength and the role of Fermi surfaces. This fundamental issue becomes especially relevant with the discovery of the iron chalcogenide (FeCh) superconductors, the only iron-based family in proximity to an insulating phase. Here, we use angle-resolved photoemission spectroscopy (ARPES) to measure three representative FeCh superconductors, FeTe0.56Se0.44, K0.76Fe1.72Se2, and monolayer FeSe film grown on SrTiO3. We show that, these FeChs are all in a strongly correlated regime at low temperatures, with an orbital-selective strong renormalization in the dxy bands despite having drastically different Fermi-surface topologies. Furthermore, raising temperature brings all three compounds from a metallic superconducting state to a phase where the dxy orbital loses all spectral weight while other orbitals remain itinerant. These observations establish that FeChs display universal orbital-selective strong correlation behaviors that are insensitive to the Fermi surface topology, and are close to an orbital-selective Mott phase (OSMP), hence placing strong constraints for theoretical understanding of iron-based superconductors.

Who knew! And when did they know it?

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FeSb2 – Colossal Thermopower – Phonon Drag – In Gap States

by Tommy on 11/06/2015

Unified picture for the colossal thermopower compound FeSb2, M. Battiato, J. M. Tomczak, Z. Zhong and K. Held

We identify the driving mechanism of the gigantic Seebeck coefficient in FeSb2 as the phonon-drag effect associated with an in-gap density of states that we demonstrate to derive from excess iron. We accurately model electronic and thermoelectric transport coefficients and explain the so far ill-understood correlation of maxima and inflection points in different response functions. Our scenario has far-reaching consequences for attempts to harvest the spectacular powerfactor of FeSb2.

Another piece of the puzzle falls into place.

This is a race now.

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Ocean Dynamics, Carbon Ventilation and Bipolar Seesaws

by Tommy on 10/06/2015

An Atlantic–Pacific ventilation seesaw across the last deglaciation, E. Freeman, L.C. Skinner, A. Tisserand, T. Dokken, A. Timmermann, L. Menviel and T. Friedrich, Earth and Planetary Science Letters, 424, 237–244 (15 August 2015), doi:10.1016/j.epsl.2015.05.032

It has been proposed that the rapid rise of atmospheric CO2 across the last deglaciation was driven by the release of carbon from an extremely radiocarbon-depleted abyssal ocean reservoir that was ‘vented’ to the atmosphere primarily via the deep- and intermediate overturning loops in the Southern Ocean. While some radiocarbon observations from the intermediate ocean appear to confirm this hypothesis, others appear to refute it. Here we use radiocarbon measurements in paired benthic- and planktonic foraminifera to reconstruct the benthic–planktonic 14C age offset (i.e. ‘ventilation age’) of intermediate waters in the western equatorial Atlantic. Our results show clear increases in local radiocarbon-based ventilation ages during Heinrich-Stadial 1 (HS1) and the Younger Dryas (YD). These are found to coincide with opposite changes of similar magnitude observed in the Pacific, demonstrating a ‘seesaw’ in the ventilation of the intermediate Atlantic and Pacific Oceans that numerical model simulations of North Atlantic overturning collapse indicate was primarily driven by North Pacific overturning. We propose that this Atlantic–Pacific ventilation seesaw would have combined with a previously identified North Atlantic–Southern Ocean ventilation seesaw to enhance ocean–atmosphere CO2 exchange during a ‘collapse’ of the North Atlantic deep overturning limb. Whereas previous work has emphasized a more passive role for intermediate waters in deglacial climate change (merely conveying changes originating in the Southern Ocean) we suggest instead that the intermediate water seesaw played a more active role via relatively subtle but globally coordinated changes in ocean dynamics that may have further influenced ocean–atmosphere carbon exchange.

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Flat Bands Proposed as a Model for High Tc Superconductivity

by Tommy on 10/06/2015

Occurrence of flat bands in strongly correlated Fermi systems and high-Tc superconductivity of electron-doped compounds, V.A. Khodel, J.W. Clark, K.G. Popov and V.R. Shaginyan, JETP Lett. 101, 413 (3 June 2015), DOI: 10.1134/S0021364015060065

We consider a class of strongly correlated Fermi systems that exhibit an interaction-induced flat band pinned to the Fermi surface, and generalize the Landau strategy to accommodate a flat band and apply the more comprehensive theory to electron systems of solids. The non-Fermi-liquid behavior that emerges is compared with relevant experimental data on heavy-fermion metals and electron-doped high-Tc compounds. We elucidate how heavy-fermion metals have extremely low superconducting transition temperature Tc, its maximum reached in the heavy-fermion metal CeCoIn5 does not exceed 2.3 K, and explain the enhancement of Tc observed in high-Tc superconductors. We show that the coefficient A1 of the T-linear resistivity scales with Tc, in agreement with the experimental behavior uncovered in the electron-doped materials. We have also constructed schematic temperature-doping phase diagram of the copper oxide superconductor La2−xCexCuO4 and explained the doping dependence of its resistivity.

High-Tc superconductivity of electron systems with flat bands pinned to the Fermi surface, V.A. Khodel, J.W. Clark, V.R. Shaginyan and M.V. Zverev

The phenomenon of flat bands pinned to the Fermi surface is analyzed on the basis of the Landau-Pitaevskii relation, which is applicable to electron systems of solids. It is shown that the gross properties of normal states of high-Tc superconductors, frequently called strange metals, are adequately explained within the flat-band scenario. Most notably, we demonstrate that in electron systems moving in a two-dimensional Brillouin zone, superconductivity may exist in domains of the Lifshitz phase diagram lying far from lines of critical antiferromagnetic fluctuations, even if the effective electron-electron interaction in the Cooper channel is repulsive.

And, of course, this can be almost immediately checked out in the quantum simulators.

Superfluidity in topologically nontrivial flat bands, Sebastiano Peotta and Päivi Törmä

Topological invariants built from the periodic Bloch functions characterize new phases of matter, such as topological insulators and topological superconductors. The most important topological invariant is the Chern number that explains the quantized conductance of the Quantum Hall Effect. Here, we provide a general expression for the superfluid weight Ds of a multiband superconductor that is applicable to topologically nontrivial bands with nonzero Chern number C. We find a new invariant calculated from the Bloch functions that gives the superfluid weight in a flat band, with the bound Ds ≥ |C|. Thus, even a flat band can carry finite superfluid current, provided the Chern number is non-zero. As an example, we provide Ds for the time-reversal invariant attractive Harper-Hubbard model that can be experimentally tested in ultracold gases. In general, our results establish that a topologically nontrivial flat band is a promising route towards room-temperature superconductivity.

Ladies and gentlemen, start your band flatteners.

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Magnetic Field Solidification Improves Bismuth Thermoelectrics

by Tommy on 9/06/2015

Melting and solidification of bismuth antimony telluride under a high magnetic field: A new route to high thermoelectric performance, Yubo Luo, Junyou Yang, , Qinghui Jiang, Liangwei Fu, Ye Xiao, WeiXin Li, Dan Zhang, Zhiwei Zhou, Yudong Cheng, Nano Energy, In Press (6 June 2015), doi:10.1016/j.nanoen.2015.05.032

Imposing an intensity variable high static magnetic field during traditional melting-solidification (MS) method has been used as a new method to prepare p-type bismuth antimony telluride thermoelectric materials in this work. On this basis, we present a systematic study of the nucleation, crystal orientation, microstructure, electrical and thermal transport properties of the obtained alloy ingots solidified under different magnetic field intensities. A c-axis alignment of bismuth antimony telluride in the direction perpendicular to the magnetic field, formation of BSTII nanorods, and a simultaneous optimization of the electrical and thermal transport properties has been observed. Consequently, an enhanced ZTmax = 1.71 at 323 K has been achieved in a polycrystalline Bi0.5Sb1.5Te3 sample solidified under a 2T magnetic field.

Well there you go!

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United States Human Space Flight Program Commits Suicide

by Tommy on 4/06/2015
SLS - Stupid Launch System

SLS – Stupid Launch System

These people have lost their fucking minds.

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Incoherent Unparticles Revolutionize Theoretical Physics

by Tommy on 3/06/2015

Power-law Optical Conductivity in the Cuprates from Unparticle Stuff, Kridsanaphong Limtragool and Philip Phillips

We calculate the optical conductivity using several models for unparticle or scale-invariant matter. Within a Gaussian action for unparticles that is gauged with Wilson lines, we find that the conductivity computed from the Kubo formalism with vertex corrections yields no non-trivial deviation from the free-theory result. This result obtains because at the Gaussian level, unparticles are just a superposition of particle fields and hence any transport property must be consistent with free theory. Beyond the Gaussian approach, we adopt the continuous mass formulation of unparticles and calculate the Drude conductivity directly. We obtain an algebraic conductivity that scales as ω−2/3 and the associated phase angle between the imaginary and real parts of arctan σ21 = 60° precisely as is seen in the cuprates. Given the recent results {Donos 2014, Rangamani 2015, Langley} that gravitational crystals lack a power-law optical conductivity, this constitutes the first account of the ω−2/3 conductivity and the phase angle seen in optimally doped cuprates. Our result indicates that it is the incoherent background that is responsible for the power law conductivity in the cuprates.

I have way too much stuff.

Incoherent does not even begin to describe it.

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Spin Polarons Proposed Again for Cuprate Superconductivity

by Tommy on 1/06/2015

The low-energy physics of the cuprates from first principles quantum Monte Carlo calculations, Lucas K. Wagner

The author reports on new high-fidelity simulations of charge carriers in the high-Tc cuprate materials using quantum Monte Carlo techniques applied to the first principles Hamiltonian. With this new application of this high accuracy technique, the doped ground state is found to be in the form of a spin polaron, in which charge is localized through a strong interaction with the spin. This spin polaron has calculated properties largely similar to the phenomenology of the cuprates, and may be the object which forms the Fermi surface in these materials. The results contained in this paper comprise an accurate first principles derived paradigm from which to study superconductivity in the cuprates.

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The 2015 Parade of Planets – Up Next – The Tenth Planet Pluto

by Tommy on 31/05/2015
The Tenth Planet Planetary System Pluto Plutoid Plutoids

The Tenth Planet Planetary System Pluto Plutoid Plutoids

Don’t miss the Open House on July 14th.

Everything must go!

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The Fifth Planet Ceres is Now Revealed in Exquisite Detail

by Tommy on 31/05/2015
The Fifth Planet Ceres

The Fifth Planet Ceres

One can now see a giant canyon slumping from the east into the crater with the interior vents.

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Bismuth Adatoms on Graphene on Silicon Carbide Studied

by Tommy on 30/05/2015

Long-range interactions of bismuth growth on monolayer epitaxial graphene at room temperature, H. -H. Chen, S. H. Su, S. -L. Chang, B. -Y. Cheng, C. -W. Chong, J. C. A. Huang and M. -F. Lin, Carbon, Volume 93, Pages 180–186 (November 2015) doi:10.1016/j.carbon.2015.05.052

Long-range electronic interaction between Bismuth (Bi) adatoms on graphene formed on a 4H-SiC (0 0 0 1) substrate are clearly observed at room temperature (T = 300 K). Using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we have demonstrated that such oscillatory interaction results mainly from the mediation of graphene Dirac-like electrons and the effect of the corrugated surface of SiC substrate. These two factors cause the observed oscillatory interaction with characteristic distribution distances and linear arrangements of Bi adatoms. The present study sheds light on understanding and controlling the nucleation of adatoms and subsequent growth of nanostructures on graphene surface.

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Crystal Structure of Hexagonal Diamond Lonsdaleite Refined

by Tommy on 30/05/2015

Extent of stacking disorder in diamond, Christoph G. Salzmann, Benjamin J. Murray and Jacob J. Shephard

Hexagonal diamond has been predicted computationally to display extraordinary physical properties including a hardness that exceeds cubic diamond. However, a recent electron microscopy study has shown that so-called hexagonal diamond samples are in fact not discrete materials but faulted and twinned cubic diamond. We now provide a quantitative analysis of cubic and hexagonal stacking in diamond samples by analysing X-ray diffraction data with the DIFFaX software package. The highest fractions of hexagonal stacking we find in materials which were previously referred to as hexagonal diamond are below 60%. The remainder of the stacking sequences are cubic. We show that the cubic and hexagonal sequences are interlaced in a complex way and that naturally occurring Lonsdaleite is not a simple phase mixture of cubic and hexagonal diamond. Instead, it is structurally best described as stacking disordered diamond. The future experimental challenge will be to prepare diamond samples beyond 60% hexagonality and towards the so far elusive ‘perfect’ hexagonal diamond.

Science marches on, better late than never. Unobtainium will soon be available.

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Freshwater Forcing Refined Through Two Interglacial Transitions

by Tommy on 30/05/2015

Offset Timing of Climate Oscillations During the Last two Glacial-Interglacial Transitions Connected with Large-Scale Freshwater Perturbation, Patricia Jimenez-Amat and Rainer Zahn, Accepted for Publication in Paleoceanography (26 May 2015), DOI: 10.1002/2014PA002710

Multi-decadal to centennial planktic 18O and Mg/Ca records were generated at ODP976 in the Alboran Sea. The site is in the flow path of Atlantic inflow waters entering the Mediterranean and captured North Atlantic signals through the surface inflow and the atmosphere. The records reveal similar climatic oscillations during the last two glacial-to-interglacial transitions, albeit with a different temporal pacing. Glacial termination 1 (T1) was marked by Heinrich event 1 (H1), post-H1 Bolling/Allerod (B/A) warming and Younger Dryas (YD) cooling. During T2 the H11 18O anomaly was twice as high and lasted 30% longer than during H1. The post-H11 warming marked the start of MIS5e while the subsequent YD-style cooling occurred during early MIS5e. The post-H11 temperature increase at ODP976 matched the sudden Asian Monsoon Termination II at 129 ka BP. Extending the 230Th-dated speleothem timescale to ODP976 suggests glacial conditions in the Northeast Atlantic region were terminated abruptly and interglacial warmth was reached in less than a millennium. The early-MIS5e cooling and freshening at ODP976 coincided with similar changes at North Atlantic sites suggesting this was a basin-wide event. By analogy with T1 we argue that this was a YD-type event that was shifted into the early stages of the last interglacial period. This scenario is consistent with evidence from northern North Atlantic and Nordic Sea sites that the continuing disintegration of the large Saalian Stage (MIS6) ice sheet in Eurasia delayed the advection of warm North Atlantic waters and full-strength convective overturn until later stages of MIS5e.

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Black Phosphorus is the New Bismuth and Graphite

by Tommy on 29/05/2015

Anomalous Quantum Transport Properties in Semimetallic Black Phosphorus, Kazuto Akiba, Astushi Miyake, Yuichi Akahama, Kazuyuki Matsubayashi, Yoshiya Uwatoko, Hayato Arai, Yuki Fuseya and Masashi Tokunaga, To Be Published in J. Phys. Soc. Jpn

Magnetoresistance in single crystals of black phosphorus is studied at ambient and hydrostatic pressures. In the semiconducting states at pressures below 0.71 GPa, the magnetoresistance shows periodic oscillations, which can be ascribed to the magneto-phonon resonance that is characteristic of high mobility semiconductors. In the metallic state above 1.64 GPa, the both transverse and longitudinal magnetoresistance show titanic increase with exhibiting superposed Shubnikov-de Haas oscillations. The observed small Fermi surfaces, high mobilities and light effective masses of carriers in semimetallic black phosphorus are comparable to those in the representative elemental semimetals of bismuth and graphite.

I am beginning to detect a pattern here.

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Non-Phonon Pairing and Scattering Channels in High Tc Studied

by Tommy on 29/05/2015

Inequivalence of Single-Particle and Population Lifetimes in a Cuprate Superconductor
Shuolong Yang, Jonathan A. Sobota, Dominik Leuenberger, Yu He, Makoto Hashimoto, Donghui Lu, Hiroshi Eisaki, Patrick S. Kirchmann and Zhi-Xun Shen, Accepted by Physical Review Letters

We study optimally doped Bi-2212 (Tc = 96 K) using femtosecond time- and angle-resolved photoelectron spectroscopy. Energy-resolved population lifetimes are extracted and compared with single-particle lifetimes measured by equilibrium photoemission. The population lifetimes deviate from the single-particle lifetimes in the low excitation limit by one to two orders of magnitude. Fundamental considerations of electron scattering unveil that these two lifetimes are in general distinct, yet for systems with only electron-phonon scattering they should converge in the low-temperature, low-fluence limit. The qualitative disparity in our data, even in this limit, suggests that scattering channels beyond electron-phonon interactions play a significant role in the electron dynamics of cuprate superconductors.

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