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Condense matter

Joel D Cox, Andrea Marini, F Javier García de Abajo
High-harmonic generation in condensed-matter systems is both a source of fundamental insight into quantum electron motion and a promising candidate to realize compact ultraviolet and ultrafast light sources. While graphene is anticipated to efficiently generate high-order harmonics due to its anharmonic charge-carrier dispersion, experiments performed on extended samples using THz illumination have revealed only a weak effect. The situation is further complicated by the enormous electromagnetic field intensities required by this highly nonperturbative nonlinear optical phenomenon...
February 22, 2017: Nature Communications
Ratnadwip Singha, Arnab Kumar Pariari, Biswarup Satpati, Prabhat Mandal
Whereas the discovery of Dirac- and Weyl-type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and technological applications is an experimental challenge. In all of the reported materials, linear dispersion survives only up to a few hundred millielectronvolts from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics...
February 21, 2017: Proceedings of the National Academy of Sciences of the United States of America
Gregor Posnjak, Simon Čopar, Igor Muševič
Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere...
February 21, 2017: Nature Communications
H Legendre, H Hoste, T Gidenne
Alternative strategies to synthetic chemical drugs are needed in livestock and are a key issue in organic farming today. This study aimed at examining the potentialities of sainfoin, a legume rich in condensed tannins, as a nutraceutical that combines nutritive and antiparasitic effects in rabbits. To test the effect of infection with a helminth (I: infected groups; NI: not infected groups) and the effect of substituting 40% of the alfalfa in a control diet (C) with sainfoin (diet S), four groups of 16 weaned rabbits were arranged according to a 2×2 bifactorial design...
February 20, 2017: Animal: An International Journal of Animal Bioscience
Y X Zhao, Y Lu
Recently, Weyl fermions have attracted increasing interest in condensed matter physics due to their rich phenomenology originated from their nontrivial monopole charges. Here, we present a theory of real Dirac points that can be understood as real monopoles in momentum space, serving as a real generalization of Weyl fermions with the reality being endowed by the PT symmetry. The real counterparts of topological features of Weyl semimetals, such as Nielsen-Ninomiya no-go theorem, 2D subtopological insulators, and Fermi arcs, are studied in the PT symmetric Dirac semimetals and the underlying reality-dependent topological structures are discussed...
February 3, 2017: Physical Review Letters
Alicia J Kollár, Alexander T Papageorge, Varun D Vaidya, Yudan Guo, Jonathan Keeling, Benjamin L Lev
Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas...
February 17, 2017: Nature Communications
H Z Shen, D X Li, X X Yi
The Kubo formula is an equation that expresses the linear response of an observable due to a time-dependent perturbation. It has been extended from closed systems to open systems in recent years under the Markovian approximation, but is barely explored for open systems in non-Markovian regimes. In this paper, we derive a formula for the linear response of an open system to a time-independent external field. This response formula is available for both Markovian and non-Markovian dynamics depending on parameters in the spectral density of the environment...
January 2017: Physical Review. E
Guan Du, Jifeng Shao, Xiong Yang, Zengyi Du, Delong Fang, Jinghui Wang, Kejing Ran, Jinsheng Wen, Changjin Zhang, Huan Yang, Yuheng Zhang, Hai-Hu Wen
Topological superconductors are a very interesting and frontier topic in condensed matter physics. Despite the tremendous efforts in exploring topological superconductivity, its presence is however still under heavy debate. The Dirac electrons have been proven to exist on the surface of a topological insulator. It remains unclear whether and how the Dirac electrons fall into Cooper pairing in an intrinsic superconductor with the topological surface states. Here we show the systematic study of scanning tunnelling microscope/spectroscopy on the possible topological superconductor SrxBi2Se3...
February 15, 2017: Nature Communications
Leilei Luo, Yucang Liang, Egil Sev Erichsen, Reiner Anwander
Monodisperse and uniform high-quality MCM(Mobil Composition of Matter)-48-type CMSNs (Cubic Mesoporous Silica Nanoparticles) are readily prepared by simply optimizing the molar ratio of ethanol and surfactant in the system TEOS-CTAB-NaOH-H2O-EtOH (TEOS=tetraethyl orthosilicate, CTAB=cetyltrimethylammonium bromide, EtOH=ethanol). In the absence of ethanol only hexagonal mesoporous silica with ellipsoidal and spherical morphology are obtained. The presence of ethanol drives a mesophase transformation from hexagonal to mixed hexagonal/cubic, further to purely cubic, and finally to a mixed cubic/lamellar...
January 31, 2017: Journal of Colloid and Interface Science
Jamir Marino, Alessio Recati, Iacopo Carusotto
We theoretically propose an experimentally viable scheme to use an impurity atom in an atomic Bose-Einstein condensate, in order to realize condensed-matter analogs of quantum vacuum effects. In a suitable atomic level configuration, the collisional interaction between the impurity atom and the density fluctuations in the condensate can be tailored to closely reproduce the electric-dipole coupling of quantum electrodynamics. By virtue of this analogy, we recover and extend the paradigm of electromagnetic vacuum forces to the domain of cold atoms, showing in particular the emergence, at supersonic atomic speeds, of a novel power-law scaling of the Casimir force felt by the atomic impurity, as well as the occurrence of a quantum frictional force, accompanied by the Ginzburg emission of Bogoliubov quanta...
January 27, 2017: Physical Review Letters
Kyle E Ballantine, Benjamin L Lev, Jonathan Keeling
Previous realizations of synthetic gauge fields for ultracold atoms do not allow the spatial profile of the field to evolve freely. We propose a scheme which overcomes this restriction by using the light in a multimode cavity with many nearly degenerate transverse modes, in conjunction with Raman coupling, to realize an artificial magnetic field which acts on a Bose-Einstein condensate of neutral atoms. We describe the evolution of such a system and present the results of numerical simulations which show dynamical coupling between the effective field and the matter on which it acts...
January 27, 2017: Physical Review Letters
Hye-Youn Park, Susan Gilbreath, Edward Barakatt
BACKGROUND: Studies have shown a consistent association between exposure to traffic-related air pollution and adverse health effects. In particular, exposure can be high for cyclists who travel near roadways. The objective of the current study was to examine the relationship between short-term exposure of near-road traffic emissions and acute changes in lung function among individuals who frequently bike in the Sacramento and Davis areas in California. Ultrafine particulate matter (UFPM) was used as a surrogate for near-roadway exposure in this study since the main source of this pollutant is from motor vehicle exhaust...
February 8, 2017: Environmental Health: a Global Access Science Source
Ziqiao Wang, Chaofei Liu, Yi Liu, Jian Wang
Since the dramatic interface enhancement of superconducting transition temperature (Tc) was reported in one unit-cell FeSe film grown on SrTiO3 substrate (1-UC FeSe/STO) by molecular beam epitaxy (MBE), related research on this system has become a new frontier in condensed matter physics. In this paper, we present a brief review on this rapidly developing field, mainly focusing on the superconducting properties of 1-UC FeSe/STO. Experimental evidences for the high-temperature superconductivity in 1-UC FeSe/STO, including the direct evidences revealed by transport and diamagnetic measurements, and other evidences from scanning tunneling microscope (STM) and angle-resolved photoemission spectroscopy (ARPES), are overviewed...
February 8, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Daniel O Brodsky, Mark E Barber, Jan A N Bruin, Rodolfo A Borzi, Santiago A Grigera, Robin S Perry, Andrew P Mackenzie, Clifford W Hicks
A major area of interest in condensed matter physics is the way electrons in correlated electron materials can self-organize into ordered states, and a particularly intriguing possibility is that they spontaneously choose a preferred direction of conduction. The correlated electron metal Sr3Ru2O7 has an anomalous phase at low temperatures that features strong susceptibility toward anisotropic transport. This susceptibility has been thought to indicate a spontaneous anisotropy, that is, electronic order that spontaneously breaks the point-group symmetry of the lattice, allowing weak external stimuli to select the orientation of the anisotropy...
February 2017: Science Advances
Elizabeth Fireman, Rinat Edelheit, Moshe Stark, Amir Bar Shai
Ultrafine particles (UFP) have been postulated to significantly contribute to the adverse health effects associated with exposure to particulate matter (PM). Due to their extremely small size (aerodynamic diameter <100 nm), UFP are able to deposit deep within the lung after inhalation and evade many mechanisms responsible for the clearance of larger particles. There is a lack of biologically relevant personal exposure metrics for exposure to occupational- and environmental-related micro- and nano-sized PM...
2017: Journal of Nanoparticle Research: An Interdisciplinary Forum for Nanoscale Science and Technology
Yue Zheng, W J Chen
Topological defects in condense matters are gathering intensive attention due to their important roles in phase transition and fascinating characteristics. Among the various matters, ferroics which possess a switchable physical characteristic and form domain structures, are ideal systems to form topological defects. In particular, a special class of topological defects-vortices-have been found exist commonly in ferroics. They often manifest themselves as singular regions where domains merge in large systems, or stabilize as novel order states instead of forming domain structures in small enough systems...
February 3, 2017: Reports on Progress in Physics
Fergus J M Rogers, Pierre-François Loos
Wigner crystals (WCs) are electronic phases peculiar to low-density systems, particularly in the uniform electron gas. Since its introduction in the early twentieth century, this model has remained essential to many aspects of electronic structure theory and condensed-matter physics. Although the (lowest-energy) ground-state WC (GSWC) has been thoroughly studied, the properties of excited-state WCs (ESWCs) are basically unknown. To bridge this gap, we present a well-defined procedure to obtain an entire family of ESWCs in a one-dimensional electron gas using a symmetry-broken mean-field approach...
January 28, 2017: Journal of Chemical Physics
Syu-You Guan, Peng-Jen Chen, Ming-Wen Chu, Raman Sankar, Fangcheng Chou, Horng-Tay Jeng, Chia-Seng Chang, Tien-Ming Chuang
The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity...
November 2016: Science Advances
Masayuki Ochi, Ryotaro Arita, Shinji Tsuneyuki
Obtaining accurate band structures of correlated solids has been one of the most important and challenging problems in first-principles electronic structure calculation. There have been promising recent active developments of wave function theory for condensed matter, but its application to band-structure calculation remains computationally expensive. In this Letter, we report the first application of the biorthogonal transcorrelated (BITC) method: self-consistent, free from adjustable parameters, and systematically improvable many-body wave function theory, to solid-state calculations with d electrons: wurtzite ZnO...
January 13, 2017: Physical Review Letters
Ranga P Dias, Isaac F Silvera
Producing metallic hydrogen has been a great challenge to condensed matter physics. Metallic hydrogen may be a room temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 GPa hydrogen becomes metallic with reflectivity as high as 0.91. We fit the reflectance using a Drude free electron model to determine the plasma frequency of 32.5 ± 2...
January 26, 2017: Science
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