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Iliya V Getmanskii, Vitaliy V Koval, Alexander I Boldyrev, Ruslan M Minyaev, Vladimir I Minkin
New metastable crystalline forms of the supertetrahedral Al4X (X=B, C, Al, Si) solids have been computationally designed using density functional theory calculations with imposing of periodic boundary conditions. The geometric and electronic structures of the predicted new systems were calculated on the basis of the diamond lattice in which all carbon atoms are replaced by the Al4X structural units, where X is boron, carbon, aluminum and silicon atoms. The calculations showed that the dynamic stability of the Al4X crystal structures critically depends on the nature of the bridging atom X: supertetrahedral Al4C and Al4Si solidsare dynamically stable, whereas Al4B and Al4Al ones are unstable...
December 14, 2018: Journal of Physical Chemistry. A
Alei Li, Qianxue Chen, Peipei Wang, Yuan Gan, Tailei Qi, Peng Wang, Fangdong Tang, Judy Z Wu, Rui Chen, Liyuan Zhang, Youpin Gong
2D atomic sheets of transition metal dichalcogenides (TMDs) have a tremendous potential for next-generation optoelectronics since they can be stacked layer-by-layer to form van der Waals (vdW) heterostructures. This allows not only bypassing difficulties in heteroepitaxy of lattice-mismatched semiconductors of desired functionalities but also providing a scheme to design new optoelectronics that can surpass the fundamental limitations on their conventional semiconductor counterparts. Herein, a novel 2D h-BN/p-MoTe2 /graphene/n-SnS2 /h-BN p-g-n junction, fabricated by a layer-by-layer dry transfer, demonstrates high-sensitivity, broadband photodetection at room temperature...
December 14, 2018: Advanced Materials
Mark Lyubarov, Alexander Poddubny
We theoretically study the dissipative Bose-Hubbard model describing the array of tunneling-coupled cavities with non-conservative photon-photon interaction. The bound two-photon states are formed in this system either in the limited range of the center-of-mass wave vectors or in the full Brillouin zone, depending on the strength of the dissipative interaction. Transition between these two regimes is manifested as an exceptional point in the complex energy spectrum. This improves fundamental understanding of the interplay of non-Hermiticity and interactions in the quantum structures and can potentially be used for on-demand nonlinear light generation in photonic lattices...
December 15, 2018: Optics Letters
Cristian D Batista, Mikhail Shifman, Zhentao Wang, Shang-Shun Zhang
We discuss noncollinear magnetic phenomena whose local order parameter is characterized by more than one spin vector. By focusing on the simple cases of 2D triangular and 3D pyrochlore lattices, we demonstrate that their low-energy theories can be described by a one-parametric class of sigma models continuously interpolating between the classical Heisenberg model and the principal chiral model Tr(∂_{a}U∂_{a}U^{†}) for all U∈SU(2). The target space can be viewed as a U(1) fibration over the CP(1) space...
November 30, 2018: Physical Review Letters
Bahadur Singh, Barun Ghosh, Chenliang Su, Hsin Lin, Amit Agarwal, Arun Bansil
Materials with tunable charge and lattice degrees of freedom provide excellent platforms for investigating multiple phases that can be controlled via external stimuli. We show how the charge-ordered ferroelectric oxide Ag_{2}BiO_{3}, which has been realized experimentally, presents a unique exemplar of a metal-insulator transition under an external electric field. Our first-principles calculations, combined with a symmetry analysis, reveal the presence of a nearly ideal hourglass-Dirac-semimetal state in the nonpolar structure of Ag_{2}BiO_{3}...
November 30, 2018: Physical Review Letters
Lev Vidmar, Lucas Hackl, Eugenio Bianchi, Marcos Rigol
Much has been learned about universal properties of entanglement entropies in ground states of quantum many-body lattice systems. Here we unveil universal properties of the average bipartite entanglement entropy of eigenstates of the paradigmatic quantum Ising model in one dimension. The leading term exhibits a volume-law scaling that we argue is universal for translationally invariant quadratic models. The subleading term is constant at the critical field for the quantum phase transition and vanishes otherwise (in the thermodynamic limit); i...
November 30, 2018: Physical Review Letters
Jin-Jian Zhou, Olle Hellman, Marco Bernardi
Structural phase transitions and soft phonon modes pose a long-standing challenge to computing electron-phonon (e-ph) interactions in strongly anharmonic crystals. Here we develop a first-principles approach to compute e-ph scattering and charge transport in materials with anharmonic lattice dynamics. Our approach employs renormalized phonons to compute the temperature-dependent e-ph coupling for all phonon modes, including the soft modes associated with ferroelectricity and phase transitions. We show that the electron mobility in cubic SrTiO_{3} is controlled by scattering with longitudinal optical phonons at room temperature and with ferroelectric soft phonons below 200 K...
November 30, 2018: Physical Review Letters
M Martinello, M Checchin, A Romanenko, A Grassellino, S Aderhold, S K Chandrasekeran, O Melnychuk, S Posen, D A Sergatskov
The discovery of nitrogen-doping treatment revealed that the radio frequency surface resistance of niobium resonators may be significantly reduced when nitrogen impurities are dissolved as interstitials in the material. A peculiar behavior exhibited by N-doped cavities is the anti-Q slope, i.e., a reduction in the temperature-dependent component of the surface resistance as a function of the accelerating field. This unusual trend in the surface resistance behavior has been attributed to the presence of interstitial nitrogen in the niobium lattice after the doping treatment...
November 30, 2018: Physical Review Letters
Eduardo V Castro, Antonino Flachi, Pedro Ribeiro, Vincenzo Vitagliano
We consider an interacting quantum field theory on a curved two-dimensional manifold that we construct by geometrically deforming a flat hexagonal lattice by the insertion of a defect. Depending on how the deformation is done, the resulting geometry acquires a locally nonvanishing curvature that can be either positive or negative. Fields propagating on this background are forced to satisfy boundary conditions modulated by the geometry and that can be assimilated by a nondynamical gauge field. We present an explicit example where curvature and boundary conditions compete in altering the way symmetry breaking takes place, resulting in a surprising behavior of the order parameter in the vicinity of the defect...
November 30, 2018: Physical Review Letters
D J Priour, N J McGuigan
Porous materials made up of impermeable grains constrain fluid flow to voids around the impenetrable inclusions. A percolation transition marks the boundary between densities of grains permitting bulk transport and concentrations blocking traversal on macroscopic scales. With dynamical infiltration of void spaces using virtual tracer particles, we treat inclusion geometries exactly. We calculate the critical number density per volume ρ_{c} for a variety of axially symmetric shapes and faceted solids with the former including cylinders, ellipsoids, cones, and tablet shaped grains from highly oblate (platelike) to highly prolate (needlelike) extremes...
November 30, 2018: Physical Review Letters
Jin Zhang, J Unmuth-Yockey, J Zeiher, A Bazavov, S-W Tsai, Y Meurice
Lattice gauge theories are fundamental to our understanding of high-energy physics. Nevertheless, the search for suitable platforms for their quantum simulation has proven difficult. We show that the Abelian Higgs model in 1+1 dimensions is a prime candidate for an experimental quantum simulation of a lattice gauge theory. To this end, we use a discrete tensor reformulation to smoothly connect the space-time isotropic version used in most numerical lattice simulations to the continuous-time limit corresponding to the Hamiltonian formulation...
November 30, 2018: Physical Review Letters
Hideki Ozawa, Shintaro Taie, Yosuke Takasu, Yoshiro Takahashi
Large-spin cold atomic systems can exhibit unique phenomena that do not appear in spin-1/2 systems. We report the observation of nearest-neighbor antiferromagnetic spin correlations of a Fermi gas with SU(N) symmetry trapped in an optical lattice. The precise control of the spin degrees of freedom provided by an optical pumping technique enables us a straightforward comparison between the cases of SU(2) and SU(4). Our important finding is that the antiferromagnetic correlation is enhanced for the SU(4)-spin system compared with SU(2) as a consequence of a Pomeranchuk cooling effect...
November 30, 2018: Physical Review Letters
Xiang-Long Qu, Bing Yan
A novel three-dimensional microporous framework, [Tb(pddb)phen(ox)0.5 ] n (Tb-MOF), was synthesized hydrothermally with V-shaped 4,4'-(pyridine-2,6-diyl)dibenzoic acid (H2 pddb), oxalate (ox), and 1,10-phenanthroline (phen). The framework of Tb-MOF features one-dimensional channels functionalized with pyridine-N Lewis base groups and the absence of coordinated and lattice water molecules in the structure. The Tb-MOF exhibits high thermostability (up to 385 °C) and chemical stability in a wide pH range (4-11) and common organic solvents as well as boiling water...
December 14, 2018: Inorganic Chemistry
Camilla Anelli, Michele R Chierotti, Simone Bordignon, Paolo Quadrelli, Daniela Marongiu, Giovanni Bongiovanni, Lorenzo Malavasi
The possible existence of mixed methylammonium (MA)/dimethylammonium (DMA) lead bromide hybrid perovskites of general formula MA1- x DMA x PbBr3 (0 ≤ x ≤ 1) was investigated. A combined X-ray diffraction and solid-state nuclear magnetic resonance approach indicates that DMA can be incorporated up to about x = 0.30 while retaining the cubic lattice of MAPbBr3 . By increasing the DMA content ( x), the absorption shows a progressive blue shift and the band gap moves from about 2.17 eV ( x = 0) to about 2.23 ( x = 0...
December 14, 2018: Inorganic Chemistry
Graeme Hansford
A conceptual design for a handheld X-ray diffraction (HHXRD) instrument is proposed. Central to the design is the application of energy-dispersive XRD (EDXRD) in a back-reflection geometry. This technique brings unique advantages which enable a handheld instrument format, most notably, insensitivity to sample morphology and to the precise sample position relative to the instrument. For fine-grained samples, including many geological specimens and the majority of common alloys, these characteristics negate sample preparation requirements...
December 1, 2018: Journal of Applied Crystallography
Takuo Okuchi, Naotaka Tomioka, Narangoo Purevjav, Kaoru Shibata
It is demonstrated that quasielastic neutron scattering is a novel and effective method to analyse atomic scale hydrogen transport processes occurring within a mineral crystal lattice. The method was previously characterized as sensitive for analysing the transport frequency and distance of highly diffusive hydrogen atoms or water molecules in condensed matter. Here are shown the results of its application to analyse the transport of much slower hydrogen atoms which are bonded into a crystal lattice as hydroxyls...
December 1, 2018: Journal of Applied Crystallography
Li Chen, Jascha A Lau, Dirk Schwarzer, Jörg Meyer, Varun B Verma, Alec M Wodtke
Using a mid-infrared emission spectrometer based on a superconducting nanowire single-photon detector (SNSPD), we observe the dynamics of vibrational energy pooling of CO adsorbed at the surface of a NaCl crystal. After exciting a majority of the CO molecules to their first vibrationally excited state (v = 1), we observe infrared emission from states up to v = 27. Kinetic Monte Carlo simulations show that vibrational energy collects in a few CO molecules at the expense of those up to eight lattice sites away by selective excitation of NaCl's transverse phonons...
December 13, 2018: Science
David S Simon, Shuto Osawa, Alexander V Sergienko
Working in the context of the Su-Schreiffer-Heeger model, the effect of topological boundaries on the structure and properties of bulk position-space wavefunctions is studied for a particle undergoing a quantum walk in a one-dimensional lattice. In particular, we consider what happens when the wavefunction reaches a boundary at which the Hamiltonian changes suddenly from one topological phase to another and construct an exact solution for the wavefunction on both sides of the boundary. The reflection and transmission coefficients at the boundary are calculated as a function of the system's hopping parameters, and it is shown that for some parameter ranges the transmission coefficient can be made very small...
December 13, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Bingchao Qin, Dongyang Wang, Wenke He, Yang Zhang, Haijun Wu, Stephen J Pennycook, Li-Dong Zhao
The simple binary compound SnSe has been reported as a robust thermoelectric material for energy conversion by showing strong anharmonicity and multiple electronic valence bands. Herein, we report a record high average ZT value > 1.6 at 300-793 K with maximum ZT values ranging from 0.8 at 300 K to 2.1 at 793 K in p-type SnSe crystals. This remarkable thermoelectric performance arises from the enhanced power factor and lowered lattice thermal conductivity through crystal structure modification via Te alloying...
December 13, 2018: Journal of the American Chemical Society
Faezeh Darbaniyan, Kaushik Dayal, Liping Liu, Pradeep Sharma
A temperature variation can electrically polarize a pyroelectric material. In its converse manifestation, the electrocaloric effect entails a change in temperature due to the application of an electric field. These phenomena have wide applications ranging from infrared detection sensors and solid-state refrigeration to energy harvesting. However, the pyroelectric-electrocaloric effect is typically observed in certain classes of hard, brittle crystalline materials that must satisfy a stringent set of lattice symmetry conditions...
December 13, 2018: Soft Matter
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