Black Phosphorus With Antimony Predicted to be a High ZT Thermoelectric

by Tommy on 28/08/2015

High thermoelectric performance can be achieved in black phosphorus, J. Zhang, H. J. Liu, L. Cheng, J. Wei, J. H. Liang, D. D. Fan, P. H. Jiang, L. Sun and J. Shi

Few-layer black phosphorus has recently emerged as a promising candidate for novel electronic and optoelectronic device. Here we demonstrate by first-principles calculations and Boltzmann theory that, black phosphorus could also have potential thermoelectric applications and a fair ZT value of 1.1 can be achieved at elevated temperature. Moreover, such value can be further increased to 5.4 by substituting P atom with Sb atom, giving nominal formula of P0.75Sb0.25. Our theoretical work suggests that high thermoelectric performance can be achieved without using complicated crystal structure or seeking for low-dimensional systems.

See also:

Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties, Bilu Liu, Marianne Köpf, Ahmad A. Abbas, Xiaomu Wang, Qiushi Guo, Yichen Jia, Fengnian Xia, Richard Weihrich, Frederik Bachhuber, Florian Pielnhofer, Han Wang, Rohan Dhall, Stephen B. Cronin, Mingyuan Ge, Xin Fang, Tom Nilges and Chongwu Zhou, To Appear in Advanced Materials (2015)

Two-dimensional (2D) layered materials with diverse properties have attracted significant interest in the past decade. The layered materials discovered so far have covered a wide, yet discontinuous electromagnetic spectral range from semimetallic graphene, insulating boron nitride, to semiconductors with bandgaps from middle infrared to visible light. Here, we introduce new layered semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into long-wavelength infrared (LWIR) regime and cannot be readily reached by other layered materials. Moreover, polarization-resolved infrared absorption and Raman studies reveal in-plane anisotropic properties of b-AsP. This family of layered b-AsP materials extend the electromagnetic spectra covered by 2D layered materials to the LWIR regime, and may find unique applications for future all 2D layered material based devices.

Clearly the time to apply industrial strength capital to this problem has arrived.

That being said, I have a hard time believing this.

Are you a believer now?

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Niobium and Tantalum Phosphides and Arsenides Studied

by Tommy on 28/08/2015

Topological surface states and Fermi arcs of the noncentrosymmetric Weyl semimetals TaAs, TaP, NbAs, and NbP, Yan Sun, Shu-Chun Wu and Binghai Yan, Submitted to Physical Review B on 22 Jul. 2015

Very recently the topological Weyl semimetal (WSM) state was predicted in the noncentrosymmetric compounds TaAs, TaP, NbAs, and NbP and soon led to photoemission and transport experiments to verify the presumed topological properties such as Fermi arcs (unclosed Fermi surfaces) and the chiral anomaly. In this work, we have performed fully \textit{ab initio} calculations of the surface band structures of these four WSM materials and revealed the Fermi arcs with spin-momentum-locked spin texture. On the (001) polar surface, the shape of the Fermi surface depends sensitively on the surface terminations (cations or anions), although they exhibit the same topology with arcs. The anion (P or As) terminated surfaces are found to fit recent photoemission measurements well. Such surface potential dependence indicates that the shape of the Fermi surface can be manipulated by depositing guest species (such as K atoms), as we demonstrate. On the polar surface of a WSM without inversion symmetry, Rashba-type spin polarization naturally exists in the surface states and leads to strong spin texture. By tracing the spin polarization of the Fermi surface, we can also distinguish Fermi arcs from trivial Fermi circles. The four compounds NbP, NbAs, TaP, and TaAs present an increasing amplitude of spin-orbit coupling (SOC) in the band structure. By comparing their surface states, we reveal the evolution of topological Fermi arcs from the spin-degenerate Fermi circle to spin-split arcs when the SOC increases from zero to a finite value. Our work will help us understand the complicated surface states of WSMs and allow us to manipulate them, especially for future spin-revolved photoemission and transport experiments.

Wow, that was quick.

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Microcavity Polaritons are Strongly Interacting

by Tommy on 28/08/2015

Polaritons are Not Weakly Interacting: Direct Measurement of the Polariton-Polariton Interaction Strength, Yongbao Sun, Yoseob Yoon, Mark Steger, Gangqiang Liu, Loren N. Pfeiffer, Ken West, David W. Snoke and Keith A. Nelson

Exciton-polaritons in a microcavity are composite two-dimensional bosonic quasiparticles, arising from the strong coupling between confined light modes in a resonant planar optical cavity and excitonic transitions, typically using excitons in semiconductor quantum wells (QWs) placed at the antinodes of the same cavity. Quantum phenomena such as Bose-Einstein condensation (BEC), quantized vortices, and macroscopic quantum states have been reported at temperatures from tens of Kelvin up to room temperatures, and polaritonic devices such as spin switches and optical transistors have also been reported. Many of these effects of exciton-polaritons depend crucially on the polariton-polariton interaction strength. Despite the importance of this parameter, it has been difficult to make an accurate experimental measurement, mostly because of the difficulty of determining the absolute densities of polaritons and bare excitons. Here we report the direct measurement of the polariton-polariton interaction strength in a very high-Q microcavity structure. By allowing polaritons to propagate over 40 μm to the center of a laser-generated annular trap, we are able to separate the polariton-polariton interactions from polariton-exciton interactions. The interaction strength is deduced from the energy renormalization of the polariton dispersion as the polariton density is increased, using the polariton condensation as a benchmark for the density. We find that the interaction strength is about two orders of magnitude larger than previous theoretical estimates, putting polaritons squarely into the strongly-interacting regime. When there is a condensate, we see a sharp transition to a different dependence of the renormalization on the density, which is evidence of many-body effects.

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Doped Iron Arsenides and Pnictides are Strongly Coupled and Percolative

by Tommy on 27/08/2015

Spatial competition of the ground states in 1111 iron pnictides, G. Lang, L. Veyrat, U. Graefe, F. Hammerath, D. Paar, G. Behr, S. Wurmehl and H.-J. Grafe

Using nuclear quadrupole resonance, the phase diagram of 1111 RFeAsO1−xFx (R=La, Ce, Sm) iron pnictides is constructed as a function of the local charge distribution in the paramagnetic state, which features low-doping-like (LD-like) and high-doping-like (HD-like) regions. Compounds based on magnetic rare earths (Ce, Sm) display a unified behavior, and comparison with La-based compounds reveals the detrimental role of static iron 3d magnetism on superconductivity, as well as a qualitatively different evolution of the latter at high doping. It is found that the LD-like regions fully account for the orthorhombicity of the system, and are thus the origin of any static iron magnetism. Orthorhombicity and static magnetism are not hindered by superconductivity but limited by dilution effects, in agreement with 2D (respectively 3D) nearest-neighbor square lattice site percolation when the rare earth is nonmagnetic (respectively magnetic). The LD-like regions are not intrinsically supportive of superconductivity, on the contrary of the HD-like regions, as evidenced by the well-defined Uemura relation between the superconducting transition temperature and the superfluid density when accounting for the proximity effect. This leads us to propose a complete description of the interplay of ground states in 1111 pnictides, where nanoscopic regions compete to establish the ground state through suppression of superconductivity by static magnetism, and extension of superconductivity by proximity effect.

One can argue that this is just one class of superconductors in this system.

But I am seeing a pattern develop here.

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Superconductivity Above 100 K Found in Phosphine PH3 at High Pressures

by Tommy on 26/08/2015

Superconductivity above 100 K in PH3 at high pressures, A.P. Drozdov, M. I. Eremets and I. A. Troyan

Following the recent discovery of very high temperature conventional superconductivity in sulfur hydride (critical temperature Tc of 203 K) we searched for superconductivity in other hydrides and found that a covalent hydride phosphine (PH3) also exhibits a high Tc > 100 K at pressure P > 200 GPa as determined from four-probe electrical measurements.

Didn’t I just predict this? Sure I did, right HERE.

At least I got something right.

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Chern-Simons Higgs Theory Describes Unusual Condensate

by Tommy on 25/08/2015

Superconductivity at Any Temperature, Mohamed M. Anber, Yannis Burnier, Eray Sabancilar, Mikhail Shaposhnikov

We construct a 2+1 dimensional model that sustains superconductivity at all temperatures. This is achieved by introducing a Chern Simons mixing term between two Abelian gauge fields A and Z. The superfluid is described by a complex scalar charged under Z, whereas a sufficiently strong magnetic field of A forces the superconducting condensate to form at all temperatures. In fact, at finite temperature, the theory exhibits Berezinsky-Kosterlitz-Thouless phase transition due to proliferation of topological vortices admitted by our construction. However, the critical temperature is proportional to the magnetic field of A, and thus, the phase transition can be postponed to high temperatures by increasing the strength of the magnetic field. This model can be a step towards realizing the long sought room temperature superconductivity.

Ok. Sure.


Wait. I see it.

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Phosphorene Band Gap Engineering and Materials Properties Modification and Evolution by Potassium Adatom Deposition

by Tommy on 25/08/2015

Observation of tunable band gap and anisotropic Dirac semimetal state in black phosphorus, Jimin Kim, Seung Su Baik, Sae Hee Ryu, Yeongsup Sohn, Soohyung Park, Byeong-Gyu Park, Jonathan Denlinger, Yeonjin Yi, Hyoung Joon Choi and Keun Su Kim, Science, 349, 6249, 723-726 (14 August 2015), DOI:10.1126/science.aaa6486

Black phosphorus consists of stacked layers of phosphorene, a two-dimensional semiconductor with promising device characteristics. We report the realization of a widely tunable bandgap in few-layer black phosphorus doped with potassium using an in-situ surface doping technique. Through band-structure measurements and calculations, we demonstrate that a vertical electric field from dopants modulates the bandgap owing to the giant Stark effect and tunes the material from a moderate-gap semiconductor to a band-inverted semimetal. At the critical field of this band inversion, the material becomes a Dirac semimetal with anisotropic dispersion, linear in armchair and quadratic in zigzag directions. The tunable band structure of black phosphorus may allow great flexibility in design and optimization of electronic and optoelectronic devices.

Monovalent alkali metal ions on a Group V monolayer.

Who would have ever guessed that.

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Scanning Tunneling Spectroscopy STM Technique Reveals the Mott Insulator to Charge Order Doping Evolution in the Cuprates

by Tommy on 25/08/2015

Peng Cai, Wei Ruan, Yingying Peng, Cun Ye, Xintong Li, Zhenqi Hao, Xingjiang Zhou, Dung-Hai Lee and Yayu Wang

A central question in the high temperature cuprate superconductors is the fate of the parent Mott insulator upon charge doping. Here we use scanning tunneling microscopy to investigate the local electronic structure of lightly doped cuprate in the antiferromagnetic insulating regime. We show that the doped charge induces a spectral weight transfer from the high energy Hubbard bands to the low energy in-gap states. With increasing doping, a V-shaped density of state suppression occurs at the Fermi level, which is accompanied by the emergence of checkerboard charge order. The new STM perspective revealed here is the cuprates first become a charge ordered insulator upon doping. Subsequently, with further doping, Fermi surface and high temperature superconductivity grow out of it.

Again, some people are not going to like this.

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The Thermoelectricity PhD Thesis of Gavin Koon Kok Wei

by Tommy on 25/08/2015

Charge and Spin Transport Studies in Graphene and Black Phosphorus, Gavin Koon Kok Wai, PhD Thesis, Department of Physics, National University of Singapore, Barbaros Özyilmaz, Advisor (2015)

PDF Download

Transport studies in graphene and black phosphorus two-dimensional systems will be explored in this thesis. Specifically, I studied the spin transport and spin characteristics of graphene subjected to an enhancement of its otherwise low intrinsic spin-orbit coupling. Taking advantage of its flexibility for engineering modification, we enhanced the spin-orbit coupling via chemical functionalization and metallic adatom decoration. With the initial aim of studying spin transport in black phosphorus which has an energy band gap, I unexpectedly uncovered black phosphorus’ potential as an outstanding thermoelectric material. Our discovery also agrees well with a recent theoretical prediction of high thermopower factor in black phosphorus. The published works on graphene spintronics described in this thesis are both scientifically enlightening and technologically promising. We have also demonstrated the first thermoelectric response in few layer black phosphorus crystals and the performance of this elemental semiconductor is comparable to the state of the art hybrid heterostructures/nanostructures.

See also:

Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus, Jing Wu, Gavin Kok Wai Koon, Du Xiang, Cheng Han, Chee Tat Toh, Eeshan S. Kulkarni, Ivan Verzhbitskiy, Alexandra Carvalho, Aleksandr S. Rodin, Steven P. Koenig, Goki Eda, Wei Chen, A. H. Castro Neto and Barbaros Özyilmaz, ACS Nano (24 July 2015), DOI:10.1021/acsnano.5b01922

Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity ∼ 3 × 1013 Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to ∼ 9 × 104 A W–1 by applying a source-drain bias (VSD) of 3 V, which is the highest ever measured in any 2D material and 107 times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature.

Also see also:

Large Frequency Change with Thickness in Interlayer Breathing Mode—Significant Interlayer Interactions in Few Layer Black Phosphorus, Xin Luo, Xin Lu, Gavin Kok Wai Koon, Antonio H. Castro Neto, Barbaros Özyilmaz, Qihua Xiong and Su Ying Quek, Nano Lett., 15 (6), 3931–3938 (11 May 2015), DOI:10.1021/acs.nanolett.5b00775

Bulk black phosphorus (BP) consists of puckered layers of phosphorus atoms. Few-layer BP, obtained from bulk BP by exfoliation, is an emerging candidate as a channel material in post-silicon electronics. A deep understanding of its physical properties and its full range of applications are still being uncovered. In this paper, we present a theoretical and experimental investigation of phonon properties in few-layer BP, focusing on the low-frequency regime corresponding to interlayer vibrational modes. We show that the interlayer breathing mode A3g shows a large redshift with increasing thickness; the experimental and theoretical results agree well. This thickness dependence is two times larger than that in the chalcogenide materials, such as few-layer MoS2 and WSe2, because of the significantly larger interlayer force constant and smaller atomic mass in BP. The derived interlayer out-of-plane force constant is about 50% larger than that of graphene and MoS2. We show that this large interlayer force constant arises from the sizable covalent interaction between phosphorus atoms in adjacent layers and that interlayer interactions are not merely of the weak van der Waals type. These significant interlayer interactions are consistent with the known surface reactivity of BP and have been shown to be important for electric-field induced formation of Dirac cones in thin film BP.

And finally, for background:

Advances in thermoelectrics: From single phases to hierarchical nanostructures and back, Mercouri G. Kanatzidis, MRS Bulletin, 40, 8, 687-695 (August 2015), Published online by Cambridge University Press, DOI:10.1557/mrs.2015.173

With more than two-thirds of utilized energy being lost as waste heat, there is compelling motivation for high-performance thermoelectric materials that can directly convert heat to electrical energy. However, over the decades, practical realization of thermoelectric materials has been limited by the hitherto low figure of merit, ZT, which governs the Carnot efficiency. This article describes our long-standing efforts to advance ZT to record levels starting from exploratory synthesis and evolving into the nanostructuring and panoscopic paradigm, which has helped to usher in a new era of investigation for thermoelectrics. The term panoscopic is meant as an attempt to integrate all length scales and multiple physical concepts into a single material. As in any other energy-conversion technology involving materials, thermoelectrics research is a challenging exercise in taming “contra-indicated” properties. Critical properties such as high electrical conductivity, thermoelectric power, low thermal conductivity, and mechanical strength do not tend to favor coexistence in a single material. How these can be achieved in certain systems leading to record values of ZT is also described. Endotaxial nanostructures and mesoscale engineering in thermoelectrics enable effective phonon scattering with negligible electron scattering. By combining all relevant length scales hierarchically, we can achieve large enhancements in thermoelectric performance. The field, however, continues to produce surprises.

Footnote: The following article is based on the MRS Medal presentation given by Mercouri G. Kanatzidis at the 2014 Materials Research Society Fall Meeting in Boston. Kanatzidis was recognized “For the discovery and development of nanostructured thermoelectric materials.”

Ok, time to move on this.

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Basic Simple Division Algebras Explained by Konrad Voelkel

by Tommy on 24/08/2015

Supplementary Text Notes

Division Algebras – Big Picture – Slogan – R, C, H and O are special.

If we consider R-algebras with some extra property or structure, like being a finite dimensional division algebra or admitting a norm or a composable quadratic form, very often all you can have are the classical four algebras of dimensions 1, 2, 4, 8.

They arise from the real numbers by the Cayley-Dickson construction, which is algebraic. As a consequence, the numbers 1, 2, 4, 8 show up elsewhere in mathematics. One example is the Hopf invariant one problem, whose solution shows that the unit spheres in R1, R2, R4, R8 are the only ones which admit a multiplication, even up to homotopy. Another prominent example of the classical division algebras showing up is the construction of exceptional groups.

This problem always bugged me when I was a kid.

It’s nice to see a modern review.

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Catagory Theory Representation of Boson Fermion Symmetries

by Tommy on 23/08/2015

A theory of 2+1D fermionic topological orders and fermionic/bosonic topological orders with symmetries, Tian Lan, Xiao-Gang Wen

We show that, up to invertible topological orders, 2+1D fermionic topological orders without symmetry and 2+1D fermionic/bosonic topological orders with symmetry G are classified by modular braided fusion category (BFC) over symmetric BFC; where the symmetric BFC describes a fermion product state without symmetry or a fermion/boson product state with symmetry G. We developed a simplified theory of modular BFC over symmetric BFC based on the fusion coefficients Nkij and spins si. This allows us to obtain a list of simple 2+1D fermionic topological orders (without symmetry). For example, we find that, up to invertible p+ip fermionic topological orders, there are only four fermionic topological orders with one non-trivial topological excitation: (1) the K=((−10)(02)) fractional quantum Hall state, (2) a Fibonacci bosonic topological order 2B14/5 stacking with a fermion product state, (3) the time-reversal conjugate of the previous one, (4) a primitive fermionic topological order that has a chiral central charge c=1/4, whose only topological excitation has a non-abelian statistics with a spin s=1/4 and a quantum dimension d=1+√2.

The universe just got a lot weirder, for me at least.

I sure am glad I studied algebraic geometry now.

Big heavy spirally wound cables in the bush.

I had a suspicion of something like this.

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Bismuth Oxyiodide BiOI is a Promising Photocatalytic Semiconductor

by Tommy on 22/08/2015

Photoelectric transport properties of BiOX (X = Cl, Br, I) semiconductors, D. Lotnyk, V. Komanicky, V. Bunda and A. Feher, 18th Conference of Czech and Slovak Physicists, Olomouc, Czech Republic, September 16–19, 2014

PDF Link

In this work transport properties of photosensitive semiconductors bismuth oxyhalides BiOX (X = Cl, Br, I) single crystals were investigated. We chose these compounds because they exhibit promising magnetooptical properties and are good substrates for both low temperature superconductor (Nb) and high temperature superconductor (YBa2Cu3O7−δ) thin films. We experimentally obtained temperature dependences of resistivity for BiOX single crystals without laser excitation and under laser excitation. We used lasers with wavelength 532 nm (or 2.33 eV) and 640 nm (1.93 eV); and measurements were performed in a in-plane and out-of-plane geometry; at a zero and 1 T magnetic fields. The most promising results were obtained for BiOI sample under both 532 nm and 640 nm laser excitations. For this sample metal-insulator transition was observed. Such behavior could be explained by the lowest indirect energy band from all three studied semiconductors gap (Eg(BiOI) = 1:85 eV; Eg(BiOBr) = 2:76 eV; Eg(BiOCl) = 3:44 eV) and the lowest Debye temperature θD ≈ 146 K (θD ≈ 168 K for BiOBr and 205 K for BiOCl).

Another Indirect PDF Link or Here.

See also:

Hierarchical structures constructed by BiOX (X = Cl, I) nanosheets on CNTs/carbon composite fibers for improved photocatalytic degradation of methyl orange, Baicheng Weng, Fenghua Xu and Jianguang Xu, Journal of Nanoparticle Research, 16, 2766 (27 November 2014), doi:10.1007/s11051-014-2766-7

A hierarchical structure (CNTs/CFs-NSs) of BiOX (X = Cl, I) nanosheets (NSs) on carbon fibers (CFs) embedded with aligned carbon nanotubes (CNTs) with improved photocatalytic activities has been developed on a large scale. In the CNTs/CFs obtained by centrifugal spinning, CNTs align along the axis of the CFs, form π–π stacking interactions with CFs and strength the electrical conductivity of CFs, which favors the electron collection and transportation. Cross-flake BiOX NSs were uniformly grown on the surface of CNTs/CFs through a successive ionic layer adsorption and reaction process. The as-prepared BiOX NSs are less than 20 nm in thickness with dominant reactive (001) facets that are almost fully exposed, promoting the photocatalytic properties. The hierarchical CNTs/CFs-NSs show 3- and 2-fold improved photocatalytic activities for degradation of methyl orange for BiOCl and BiOI compared to corresponding neat NSs, respectively, given the synergistic effects of CNTs/CFs and NSs. Moreover, these novel hierarchical structures with stable performance enhance the recycled ability for the photocatalyst.

Things to do with abundant and easily produced complex carbon nanostructures.

And bismuth oxyiodide, of course.

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The Cosmos is Filled Up with Giant Life Bearing Galaxies

by Tommy on 22/08/2015
Giant Elliptical Sombrero Galaxy

Giant Elliptical Sombrero Galaxy

The quest for cradles of life: using the fundamental metallicity relation to hunt for the most habitable type of galaxy, Pratika Dayal, Charles Cockell, Ken Rice and Anupam Mazumdar, APJ Letters, 810, L2 (21 August 2015), doi:10.1088/2041-8205/810/1/L2

The field of astrobiology has made huge strides in understanding the habitable zones around stars (Stellar Habitable Zones) where life can begin, sustain its existence and evolve into complex forms. A few studies have extended this idea by modelling galactic-scale habitable zones (Galactic Habitable Zones) for our Milky Way and specific elliptical galaxies. However, estimating the habitability for galaxies spanning a wide range of physical properties has so far remained an outstanding issue. Here, we present a “cosmobiological” framework that allows us to sift through the entire galaxy population in the local Universe and answer the question “Which type of galaxy is most likely to host complex life in the cosmos”? Interestingly, the three key astrophysical criteria governing habitability (total mass in stars, total metal mass and ongoing star formation rate) are found to be intricately linked through the “fundamental metallicity relation” as shown by SDSS (Sloan Digital Sky Survey) observations of more than a hundred thousand galaxies in the local Universe. Using this relation we show that metal-rich, shapeless giant elliptical galaxies at least twice as massive as the Milky Way (with a tenth of its star formation rate) can potentially host ten thousand times as many habitable (earth-like) planets, making them the most probable “cradles of life” in the Universe.

I think I see somebody waving!

Yes, it’s a tentacle.

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Thermal Assisted Electrocatalytic Photolysis of Carbon Nanofiber From Atmospheric Carbon Dioxide Reported

by Tommy on 21/08/2015
Electro Photo Thermo Catalytic Carbon Nanofibers From Carbon Dioxide

Electro Photo Thermo Catalytic Carbon Nanofibers From Carbon Dioxide

American Chemical Society (ACS) Press Release

One-Pot Synthesis of Carbon Nanofibers from CO2, Jiawen Ren, Fang-Fang Li, Jason Lau, Luis González-Urbina, and Stuart Licht, Nano Lett.(3 August 2015), DOI:10.1021/acs.nanolett.5b02427

Carbon nanofibers, CNFs, due to their superior strength, conductivity, flexibility, and durability have great potential as a material resource but still have limited use due to the cost intensive complexities of their synthesis. Herein, we report the high-yield and scalable electrolytic conversion of atmospheric CO2 dissolved in molten carbonates into CNFs. It is demonstrated that the conversion of CO2 → CCNF + O2 can be driven by efficient solar, as well as conventional, energy at inexpensive steel or nickel electrodes. The structure is tuned by controlling the electrolysis conditions, such as the addition of trace transition metals to act as CNF nucleation sites, the addition of zinc as an initiator and the control of current density. A less expensive source of CNFs will facilitate its adoption as a societal resource, and using carbon dioxide as a reactant to generate a value added product such as CNFs provides impetus to consume this greenhouse gas to mitigate climate change.

It’s a start. Obviously quantum physics will be able to speed this up a lot.

Unfortunately, it’s gonna cost us.

It might even hurt.

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Quantum Tunneling of Protons in Water Ice Observed at 20 K

by Tommy on 21/08/2015

Dielectric Anomaly in Ice near 20 K; Evidence of Macroscopic Quantum Phenomena, Fei Yen and Tian Gao, The Journal of Physical Chemistry Letters, 2015, 6, 2822-2825 (16 July 2015) DOI:10.1021/acs.jpclett.5b00797

H2O is one of the most important substances needed in sustaining life; but yet not much is known about its ground state. Here, a previously unidentified anomaly is identified in the form of a minimum in the imaginary part of the dielectric constant with respect to temperature near 20 K while the real part remains monotonic. Isothermal dispersion and absorption measurements show coinciding results. For the case of heavy ice (D2O), no anomaly was identified confirming an apparent isotope effect. Concerted quantum tunneling of protons is believed to be the main cause behind the reported anomaly. Our findings identify another system that exhibits macroscopic quantum phenomena of which rarely occur in nature.

20 K (Kelvin) sounds exactly right. Another hint of things to come.

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First Principles Study of Bismuth Adsorption on Graphene

by Tommy on 19/08/2015

Substrate-induced structures of bismuth adsorption on graphene: a first principle study, S. Y. Lin, S. L. Chang, H. H. Chen, S. H. Su, J. C. A. Huang and M.-F. Lin

The geometric and electronic properties of bismuth-adsorbed monolayer graphene, enriched by the strong effect of substrate, are investigated by the first-principles calculations. The six-layered substrate, corrugated buffer layer, and slightly deformed monolayer graphene are all simulated. Adatom arrangements are optimized through detailed analyses on adsorption energies and ground-state energies of various adsorption sites, revealing a hexagonal array of Bi atoms dominated by the interactions between buffer layer and monolayer graphene. Especially, bismuth clusters with a periodic image belong to a metastable structure, which only happens when bismuth atoms overcome a ∼50 meV energy barrier. These two kinds of structures agree with the scanning tunneling microscopy measurements in the variation of temperature. The density of states exhibits a finite value at the Fermi level, a dip at low energy, and a shoulder at ∼ 0.8 eV, as clearly indicated in the experimental measurements of tunneling conductance.

This is the same group working through these issues. 50 meV sounds about right, though.

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High Tc Proton Electron Kondo Singlet Lattice State Predicted

by Tommy on 18/08/2015

Emergence of a Kondo singlet state with the Kondo temperature well beyond 1,000K in the proton-embedded electron gas: Novel route to high-Tc superconductivity, Yasutami Takada, Ryo Maezono and Kanako Yoshizawa

Hydrogen in metals has attracted much attention for a long time from both basic scientific and technological points of view. Its electronic state has been investigated in terms of a proton embedded in the electron gas mostly by the local density approximation (LDA) to the density functional theory. At high electronic densities, it is well described by a bare proton H+ screened by metallic electrons (charge resonance), while at low densities two electrons are localized at the proton site to form a closed-shell negative ion H protected from surrounding metallic electrons by the Pauli exclusion principle. However, no details are known about the transition from H+ to H in the intermediate-density region. Here, by accurately determining the ground-state electron distribution n(r) by the combination of LDA and diffusion Monte Carlo simulations with the total electron number up to 170, we obtain a complete picture of the transition, in particular, a sharp transition from short-range H+ screening charge resonance to long-range Kondo-like spin-singlet resonance, the emergence of which is confirmed by the presence of an anomalous Friedel oscillation characteristic to the Kondo singlet state with the Kondo temperature TK well beyond 1,000 K. This study not only reveals interesting competition between charge and spin resonances, enriching the century-old paradigm of metallic screening to a point charge, but also discovers a long-sought novel high-TK system, opening an unexpected route to room-temperature superconductivity in a Kondo lattice made of protons.

1100 K divided by four is good enough for me.

Well there you have it, yet again!

Amazed and excited, I am.

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Hidden Fermion Found in Strongly Correlated Superconductivity

by Tommy on 18/08/2015

Hidden fermionic excitation in the superconductivity of the strongly attractive Hubbard model, Shiro Sakai, Marcello Civelli, Yusuke Nomura and Masatoshi Imada

We scrutinize the real-frequency structure of the self-energy in the superconducting state of the attractive Hubbard model within the dynamical mean-field theory. Within the strong-coupling superconducting phase which has been understood in terms of the Bose-Einstein condensation in the literature, we find two qualitatively different regions crossing over each other. In one region close to zero temperature, the self-energy depends on the frequency only weakly at low energy. On the other hand, in the region close to the critical temperature, the self-energy shows a pole structure. The latter region becomes more dominant as the interaction becomes stronger. We reveal that the self-energy pole in the latter region is generated by a coupling to a hidden fermionic excitation. The hidden fermion persists in the normal state, where it yields a pseudogap. We compare these properties with those of the repulsive Hubbard model relevant for high-temperature cuprate superconductors, showing that hidden fermions are a key common ingredient in strongly correlated superconductivity.

I am so excited. I might even be metastable.

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The Pressure Induced Metal Insulator Transition (MIT) in Lanthanum Manganite LaMnO3 is Percolative

by Tommy on 18/08/2015

Percolative Metal-Insulator Transition in LaMnO3, M. Sherafati, M. Baldini, L. Malavasi and S. Satpathy

We show that the pressure-induced metal-insulator transition (MIT) in LaMnO3 is fundamentally different from the Mott-Hubbard transition and is percolative in nature, with the resistivity obeying the percolation scaling laws. Using the Gutzwiller method to treat correlation, we find that the MIT is driven by a competition between electronic correlation and the electron-lattice interaction. With applied pressure, an inhomogeneous phase of intermixed insulating and metallic regions, consisting, respectively, of Jahn-Teller distorted and undistorted octahedra, develops and the MIT occurs when the metallic volume fraction exceeds the percolation threshold vc ≈ 0.29. High-pressure measurements establish the percolative power-law scaling for the resistivity and the temperature dependence follows the Efros-Shklovskii variable-range hopping behavior for granular materials.

Well there you go!

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Driven Non Equilibrium Quantum Criticality Investigated

by Tommy on 16/08/2015

Driven Markovian Quantum Criticality, Jamir Marino and Sebastian Diehl

We identify a new universality class in one-dimensional driven open quantum systems with a dark state. Salient features are the persistence of both the microscopic non-equilibrium conditions as well as the quantum coherence of dynamics close to criticality. This provides a non-equilibrium analogue of quantum criticality, and is sharply distinct from more generic driven systems, where both effective thermalization as well as asymptotic decoherence ensue, paralleling classical dynamical criticality. We quantify universality by computing the full set of independent critical exponents within a functional renormalization group approach.

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Adatoms on Monolayer Phosphorene Systematically Studied

by Tommy on 10/08/2015

Effective Doping of Monolayer Phosphorene by Surface Adsorption of Atoms for Electronic and Spintronic Applications, Priyank Rastogi, Sanjay Kumar, Somnath Bhowmick, Amit Agarwal and Yogesh Singh Chauhan

We study the effect of surface adsorption of 27 different adatoms on the electronic and magnetic properties of monolayer black phosphorus using density functional theory. Choosing a few representative elements from each group, ranging from alkali metals (group I) to halogens (group VII), we calculate the band structure, density of states, magnetic moment and effective mass for the energetically most stable location of the adatom on monolayer phosphorene. We predict that group I metals (Li, Na, K), and group III adatoms (Al, Ga, In) are effective in enhancing the n-type mobile carrier density, with group III adatoms resulting in lower effective mass of the electrons, and thus higher mobilities. Furthermore we find that the adatoms of transition metals Ti and Fe, produce a finite magnetic moment (1.87 and 2.31 μB) in monolayer phosphorene, with different band gap and electronic effective masses (and thus mobilities), which approximately differ by a factor of 10 for spin up and spin down electrons opening up the possibility for exploring spintronic applications.

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Digital Imaging to Revolutionize Faint Object Detection

by Tommy on 10/08/2015

Digital Tracking Observations Can Discover Asteroids Ten Times Fainter than Conventional Searches, Aren Heinze, Stanimir Metchev and Joseph Trollo, Accepted by The Astrophysical Journal

We describe digital tracking, a method for asteroid searches that greatly increases the sensitivity of a telescope to faint unknown asteroids. It has been previously used to detect faint Kuiper Belt objects using the Hubble Space Telescope and large ground-based instruments, and to find a small, fast-moving asteroid during a close approach to Earth. We complement this earlier work by developing digital tracking methodology for detecting asteroids using large-format CCD imagers. We demonstrate that the technique enables the ground-based detection of large numbers of new faint asteroids. Our methodology resolves or circumvents all major obstacles to the large-scale application of digital tracking for finding main belt and near-Earth asteroids. We find that for both asteroid populations, digital tracking can deliver a factor of ten improvement over conventional searches. Digital tracking has long been standard practice for deep Kuiper Belt surveys, but even there our methodology enables deeper integrations than have yet been attempted. Our search for main belt asteroids using a one-degree imager on the 0.9m WIYN telescope on Kitt Peak validates our methodology, delivers sensitivity to asteroids in a regime previously probed only with 4-meter and larger instruments, and leads to the detection of 156 previously unknown asteroids and 59 known objects in a single field. Digital tracking has the potential to revolutionize searches for faint moving objects ranging from the Kuiper Belt through main belt and near-Earth asteroids, and perhaps even anthropogenic space debris in low Earth orbit.

Better late than never. When do we get started?

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GoreSat DISCOVR Images Moon Lunar Transit from Solar L1

by Tommy on 5/08/2015

Otherwise known as Triana and Deep Space Climate Observatory

Ok, this satellite has already paid for itself.

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Electronic Nematic Bond Order Subjected to Penetrating Insight

by Tommy on 5/08/2015

Interatomic Coulomb interaction and electron nematic bond order in FeSe, Kun Jiang, Jiangping Hu, Hong Ding and Ziqiang Wang

We show that the Fe-Fe interatomic Coulomb repulsion V offers a natural explanation for the puzzling correlation effects in FeSe superconductors. It produces a strongly renormalized low-energy band structure where the Fermi level is remarkably close to the van Hove singularity (vHS) as observed in the high-temperature electron liquid phase experimentally. This close proximity enables the quantum fluctuations in V to induce a rotational symmetry breaking electronic bond order in the d-wave channel. We argue that the emergence of this low-temperature d-wave bond nematic state, different from the commonly discussed ferro-orbital order and spin-nematicity, has been observed recently by angle resolved photoemission experiments and discuss the implications on the electronic driven structural transition, the absence of magnetic order, and s-wave superconductivity.

Otherwise known as a the beginnings of a microscopic theory backed up by spectroscopy.

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Graphene Nanodiamond Enthalpy of Formation and Phase Equilibrium Investigated

by Tommy on 31/07/2015

Enthalpy of formation of single and multilayer graphene, S. A. Gubin, I. V. Maklashova and E. I. Zakatilova, Russian Journal of Physical Chemistry A, 89, 8, 1434-1438 (August 2015)

An approximate equation of state of nanocarbon is used to estimate changes in the enthalpy of formation of single- and multilayer graphene and the graphene-nanodiamond phase equilibrium pressure as a function of geometrical shape, number of layers, and size of a graphene nanoparticle. It is found that upon an increase in the number of layers in graphene with particle sizes of 100–300 nm, the phase equilibrium pressure falls and tends to that of graphite-diamond equilibrium. An agreement between the estimations, the data from MD simulations of the graphene-nanodiamond phase equilibrium, and experimentally measured parameters of the graphene-nanodiamond phase transition was obtained.

The Russians know this stuff.

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Substitutional Superconductivity of Im3m Cubic H3S Phase

by Tommy on 31/07/2015

Possible Superconductivity Approaching Ice Point, Yanfeng Ge, Fan Zhang and Yugui Yao

Recently BCS superconductivity at 190 K has been discovery in a highly compressed hydrogen sulfide. We use first-principles calculations to systematically examine the effects of partially substituting the chalcogenide atoms on the superconductivity of hydrogen chalcogenides under high pressures. We find detailed trends of how the critical temperature changes with increasing the V-, VI- or VII-substitution rate, which highlight the key roles played by low atomic mass and by strong covalent metallicity. In particular, a possible record high critical temperature of 280 K is predicted in a stable H3S0.925P0.075 with the Im3m structure under 250 GPa.

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Bismuth Identified As Universal Ultra Broadband Photodetector

by Tommy on 30/07/2015

Ultra-broadband and high-responsive photodetectors based on bismuth film at room temperature, J. D. Yao, J. M. Shao and G. W. Yang, Scientific Reports, 5, 12320 (21 July 2015), doi:10.1038/srep12320

Bismuth (Bi) has undergone researches for dozens of years on account of its abundant physics including the remarkably high mobility, exceptional large positive magnetoresistance and the coexistence of an insulating interior as well as metallic surfaces. Very recently, two-dimensional topologically-protected surface states immune to nonmagnetic perturbation such as surface oxidation and impurity scattering were experimentally demonstrated through systematic magnetotransport measurements, e.g. weak antilocalization effect and angular dependent Shubnikov-de Haas oscillations. Such robust metallic surface states, which are efficient in carrier transportation, along with its small bulk gap (14 meV) make Bi favored for high-responsive broadband photodetection. Here, we for the first time demonstrate the stable ultra-broadband photoresponse from 370 nm to 1550 nm with good reproducibility at room temperature based on a Bi photodetector. The fabricated device’s responsivity approaches 250 mA/W, accompanied with a rise time of 0.9 s and a decay time of 1.9 s. The photocurrent is linear dependent on the voltage and incident power, offering good tunability for multi-purpose applications. Thickness-dependent conductance and photocurrent reveal that the bulk is the optically active layer while the surface channel is responsible for carrier transportation. These findings pave an avenue to develop ultra-broadband Bi photodetectors for the next-generation multifunctional optoelectronic devices.

Well whaddya know!

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Magnetic Field Driven Quantum Phase Transition Discovered in Weyl Semimental Tantalum Mono Phosphide TaP

by Tommy on 30/07/2015

Chenglong Zhang, Ziquan Lin, Cheng Guo, Su-Yang Xu, Chi-Cheng Lee, Hong Lu, Shin-Ming Huang, Guoqing Chang, Chuang-Han Hsu, Hsin Lin, Liang Li, Chi Zhang, Titus Neupert, M. Zahid Hasan, Junfeng Wang and Shuang Jia

Magnetic fields perturb the motion of charged quasi-particles in solids in different ways including driving a quantum phase transition to a new state. Well-known examples include the integer and fractional quantum Hall effects and the magnetic field-induced quantum phase transitions in topologically trivial semimetals such as graphite and bismuth. A Weyl semimetal provides the first-ever realization of Weyl fermions. Such an exotic metal is characterized by the topological charges, which are momentum space monopoles and anti-monopoles that arise from the distinct chiralities of the Weyl fermions. Here we report a new quantum phase transition that arises from the Weyl fermionic quasiparticles in the Weyl semimetal tantalum monophosphide, TaP, under an intense magnetic field. We observed a sharp sign reversal of the Hall resistivity when the Weyl fermions are confined to the lowest Landau level. In this exotic chiral electron subband of a Weyl semimetal, which was never been studied experimentally beforehand, the Weyl fermions form an unexpected, collective state whose contribution to the Hall signal suddenly vanishes at a critical magnetic field (H) where the Weyl fermions enter the lowest Landau level. Our results taken collectively represent the first magnetic-field-driven quantum phase transition in a 3D bulk topological material and may suggest the emergence of new topological phases due to electronic correlations.

Note: According to the records in Wuhan High Magnetic Field Lab, the first signature of condensation was observed in March 18, 2015.

Whoa! Heads up everybody.

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Existing Thermoelectrics Optimized For Electronic Microcooling

by Tommy on 30/07/2015

Performance and mass optimization of thermoelectric microcoolers, Yee Rui Koh, Kazuaki Yazawa and Ali Shakouri, International Journal of Thermal Sciences 97, 143–151 (November 2015)

We report a scalable and parametric analysis of thermoelectric (TE) microcoolers for hotspot cooling based on analytic formulations. Design for minimizing cooling power and least mass or cost of TE material is an ultimate goal for electronic devices that require spot cooling beyond that provided by passive heat transport to the thermal ground. Performance of thermoelectric hotspot cooling on electronic devices depends on external thermal resistances, physical dimension (thickness) of the thermoelectric element, and the applied drive current. Active cooling located at the hotspot minimizes the cooling power and the internal heat generation from the TE element and also minimizes the additional driving power used for heat rejection with a preexisting air-cooling fan or a liquid-cooling pump. Electronic devices are required to operate below a specific temperature for functionality and high reliability. The hotspot cooler must be designed to deal with the amount of heat generated from the heat source with this temperature constraint. We investigate two design cases: 1) the maximum cooling and 2) the minimum drive current for a given hotspot temperature to obtain an improved coefficient-of-performance (COP). The study explores the impact of individual thermoelectric material properties, i.e. Seebeck coefficient, electrical conductivity, and thermal conductivity to find the direction that should be taken with engineered materials. We show that COP up to 8 is possible for hotspot heat fluxes of about 80 W/cm2, if TE leg thickness is optimized to ∼ 20–30 microns with today’s Bi2Te3 material. Model shows that COP > 2–3 is possible for hotspot heat fluxes bigger than 200–300 W/cm2. We find that lowering the thermal conductivity have the greatest impact, resulting in a thinner element (and therefore lower cost) while maintaining the same figure-of-merit (ZT).

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Ceres Bright Crater Spots Actively Subliming Water Vapor Haze

by Tommy on 30/07/2015
Fifth Planet Ceres Topographic Map

Fifth Planet Ceres Topographic Map

Thunderbirds are go!

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Small Water Covered Life Bearing Terrestrial Planet Discovered

by Tommy on 20/07/2015
The Planet Earth - Third Rock From The Sun

The Planet Earth – Third Rock From The Sun

It’s called Terra by offworlders.

Earth by residents.

See also: The Sun – A Star Called Sol. The Moon – Luna.

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Discovery of a Weyl Fermion Semimetal Officially Announced

by Tommy on 19/07/2015

Princeton University Press Release

Discovery of a Weyl Fermion semimetal and topological Fermi arcs, Su-Yang Xu, Ilya Belopolski, Nasser Alidoust, Madhab Neupane, Guang Bian, Chenglong Zhang, Raman Sankar, Guoqing Chang, Zhujun Yuan, Chi-Cheng Lee, Shin-Ming Huang, Hao Zheng, Jie Ma, Daniel S. Sanchez, BaoKai Wang, Arun Bansil, Fangcheng Chou, Pavel P. Shibayev, Hsin Lin, Shuang Jia and M. Zahid Hasan, Science (16 July 2015), DOI: 10.1126/science.aaa9297

A Weyl semimetal is a crystal which hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, TaAs. Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science.

I had covered this earlier but now it’s official, I guess.

See also:

Experimental observation of Weyl points, Ling Lu, Zhiyu Wang, Dexin Ye, Lixin Ran, Liang Fu, John D. Joannopoulos and Marin Soljačić, Science (16 July 2015), DOI: 10.1126/science.aaa9273

The massless solutions to the Dirac equation are described by the so-called Weyl Hamiltonian. The Weyl equation requires a particle to have linear dispersion in all three dimensions (3D) while being doubly degenerate at a single momentum point. These Weyl points are topological monopoles of quantized Berry flux exhibiting numerous unusual properties. We performed angular-resolved microwave transmission measurements through a double-gyroid photonic crystal with inversion-breaking, where Weyl points have been theoretically predicted to occur. The excited bulk states show two linear dispersion bands touching at four isolated points in the 3D Brillouin zone, indicating the observation of Weyl points. This work paves a way to a variety of photonic topological phenomena in 3D.

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Two Dimensional Majorana Fermions Come in Two Flavors

by Tommy on 16/07/2015

Classification of Majorana Fermions in Two-Dimensional Topological Superconductors, Qiu-Bo Cheng, Jing He and Su-Peng Kou

Recently, Majorana Fermions (MFs) have attracted intensive attention due to their exotic statistics and possible applications in topological quantum computation (TQC). They are proposed to exist in various two-dimensional (2D) topological systems, such as px+ipy topological superconductor and nanowire-superconducting hybridization system. In this paper, two types of Majorana Fermions with different polygon sign rules are pointed out. A “smoking gun” numerical evidence to identify MF’s classification is presented through looking for the signature of a first order topological quantum phase transition. By using it, several 2D topological superconductors are studied.

Yum. I’ll take the left one.

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High Resolution ARPES Detects Cuprate Nodal Preformed Pairing State

by Tommy on 16/07/2015

Point nodes persisting far beyond Tc in Bi2212, Takeshi Kondo, W. Malaeb, Y. Ishida, T. Sasagawa, H. Sakamoto, Tsunehiro Takeuchi, T. Tohyama and S. Shin, Nature Communications 6, 7699 (9 July 2015), DOI: 10.1038/ncomms8699

In contrast to a complex feature of antinodal state, suffering from competing order(s), the “pure” pairing gap of cuprates is obtained in the nodal region, which therefore holds the key to the superconducting mechanism. One of the biggest question is whether the point nodal state as a hallmark of d-wave pairing collapses at Tc like the BCS-type superconductors, or it instead survives above Tc turning into the preformed pair state. A difficulty in this issue comes from the small magnitude of the nodal gap, which has been preventing experimentalists from solving it. Here we use a laser ARPES capable of ultrahigh energy resolution, and detect the point nodes surviving far beyond Tc in Bi2212. By tracking the temperature evolution of spectra, we reveal that the superconductivity occurs when the pair breaking rate is suppressed smaller than the single particle scattering rate on cooling, which governs the value of Tc in cuprates.

This results sets the maximum Tc of the quasi-2D cuprate family of superconductors.

Some people are not gonna like this.

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Happy Day After The Tenth Planet Pluto Day – July 15th, 2015

by Tommy on 15/07/2015
Charon - Moon of Pluto

Charon – Moon of Pluto

Plutoids – They’re everywhere.

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