Defect two-level systems (TLS) ensembles are well known to be responsible for the low-frequency noise in solid-state mesoscopic devices, but are generally considered to be non-interacting. A model based on interactions between TLS, believed to reside in the surface oxide covering the superconducting material, provides a novel mechanism to explain the noise fluctuations that are present in virtually all superconducting circuit designs, the origins of which have remained elusive so far.

[Phys. Rev. B 92, 035442] Published Fri Jul 31, 2015

]]>EuTiO${}_{3}$ has been attracting considerable attention due to its large magnetoelectric effect and its potential for future applications. In this work the authors focus on the structural phase transition that bears resemblance to the prototypical phase transition in isostructural SrTiO${}_{3}$ but takes place at much higher temperatures ${T}_{S}$. The authors perform a detailed study of poly- and single-crystalline EuTiO${}_{3}$ and EuTi${}_{1-x}$Nb${}_{x}$O${}_{3}$ using synchrotron X-ray diffraction, Resonant Ultrasound Spectroscopy, and magnetization measurements. They find an unexpectedly rapid increase of ${T}_{S}$ when EuTiO${}_{3}$ is doped with niobium. Another notable result of the Nb doping, which is confirmed in this study for single-crystalline samples, is an unusual transformation of the low-temperature phase from an antiferromagnetic to ferromagnetic state at $x=0.1$.

[Phys. Rev. B 92, 024109] Published Thu Jul 30, 2015

]]>Quantum oscillations measurements on PdCrO${}_{2}$ show that the Fermi surface of the antiferromagnetically ordered state is a consequence of reconstruction of the Fermi surface of the unordered state.

[Phys. Rev. B 92, 014425] Published Wed Jul 29, 2015

]]>Motivated by the question of topological classification in interacting models the authors study an exactly solvable two-leg ladder model of spinless fermions with attractive interactions and find its ground states and correlation functions. They also demonstrate the appearance of topologically protected edge states and derive their braiding properties on a microscopic level.

[Phys. Rev. B 92, 041118(R)] Published Wed Jul 29, 2015

]]>Magnetic tunnel junctions (MTJs) are the building blocks of the magnetic random access memory technology due to their large contrast of the electrical resistances between the two different magnetic configurations. This work is focused on their configuration-dependent thermal properties. For the first time, the magneto-Peltier effect, a reciprocal effect of the magneto-Seebeck effect in magnetic tunnel junctions, is detected experimentally. These results open up the possibility of a magnetically controllable cooling mechanism in MTJs, which can be potentially applied in novel magnetic logic devices.

[Phys. Rev. B 92, 020414(R)] Published Tue Jul 28, 2015

]]>By exploiting epitaxial stabilization for materials synthesis in combination with $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ angle-resolved photoemission spectroscopy, the authors study the doping evolution of the archetypal infinite-layer cuprate Sr${}_{1-x}$La${}_{x}$CuO${}_{2}$ and uncover a surface reconstruction that is likely related to its polar structure.

[Phys. Rev. B 92, 035149] Published Tue Jul 28, 2015

]]>After the discovery of a 2D electron gas at the interface between LaAlO${}_{3}$ and SrTiO${}_{3}$, a great effort has been devoted to the investigation of possible routes to manipulate this system in order to exploit its interesting properties in practical applications. In this work the authors use a Landau model to show that a similar 2-dimensional electron gas may spontaneously form at ferroelectric interfaces. Unlike in the case of the LaAlO${}_{3}$/SrTiO${}_{3}$ interface, the properties of this system can be tuned in a nonvolatile way with the application of an electric field through its coupling with the ferroelectric polarization. This, for instance, would allow to induce a metal/insulator transition or to switch between an electron and a hole gas using an electric field. Such properties open new avenues for the use of 2D electron gases in oxide interfaces.

[Phys. Rev. B 92, 035438] Published Tue Jul 28, 2015

]]>Convincing experimental data show that CaMn${}_{2}$Al${}_{10}$ presents itinerant Mn-magnetism on the cusp of ferromagnetic order, opening up a new material to explore the relationship between quantum criticality and possible exotic ground states.

[Phys. Rev. B 92, 020413(R)] Published Fri Jul 24, 2015

]]>Two- and three-dimensional semi-metallic systems have recently emerged as an exciting arena in which to explore the effects of interactions in itinerant electron systems, and to advance the understanding of competing orders in strongly correlated materials. In this work, a study of the critical behavior of a three-dimensional parabolic semimetal in proximity to a quantum phase transition into a ferromagnetic phase demonstrates that the quantum critical point is unstable toward the formation of an incommensurate spin density wave phase.

[Phys. Rev. B 92, 035137] Published Tue Jul 21, 2015

]]>Inspired by helicity dependent optical phenomena in chiral metamaterials the authors exploit the idea of helicity degree of freedom of Dirac fermions. They perform a first-principles study of SnTe films and show that giant helicity splitting in the band structures can be induced under moderate electric field. They suggest using helicity as an extra degree of freedom for helicity-resolved filtering and focusing of Dirac fermions.

[Phys. Rev. B 92, 041408(R)] Published Tue Jul 21, 2015

]]>High-performance refractory materials play an important role in applications ranging from gas turbines to heat shields for hypersonic vehicles. The authors carried out an extensive first-principles investigation into the melting temperatures of the refractory Hf-C and Hf-Ta-C systems, which hold the highest melting temperatures known to date, and identified the major factors that contribute to the high melting temperatures. A new class of materials were proposed and explored, which, according to the calculation, may increase the current melting point record by up to 200 K. This work demonstrates the feasibility and usefulness of large-scale first-principles calculations for high-throughput materials screening on a high-level thermodynamic property.

[Phys. Rev. B 92, 020104(R)] Published Mon Jul 20, 2015

]]>Exploration of novel phenomena in oxides with strong spin-orbit coupling is one of the hot topics in condensed matter physics. The authors theoretically study the macroscopic magnetic anisotropy induced by fluctuations. By considering a spin model on fcc lattice with direction-dependent interactions, which may serve as an effective model for insulating magnetic oxides with strong spin-orbit coupling, they discover of a novel behavior in spin models with direction-dependent interaction.

[Phys. Rev. B 92, 020411(R)] Published Mon Jul 20, 2015

]]>The authors report structural, transport, magnetic and thermodynamic properties of of single-crystalline samples of Rb${}_{2}$Cr${}_{3}$As${}_{3}$ in both the normal and superconducting states. By compare them with those of K${}_{2}$Cr${}_{3}$As${}_{3}$ they argue for the evidence of reduced dimensionality and the ability to control it by structural tuning.

[Phys. Rev. B 92, 020508(R)] Published Mon Jul 20, 2015

]]>Although a century has passed since the celebrated Einstein - de Haas experiments, the microscopic mechanisms leading to the conversion of the spin angular momentum to the mechanical angular momentum in elastic solids has not been fully understood. In this paper D. A. Garanin and E. M. Chudnovsky explore the concept of the phonon spin recently suggested by L. Zhang and Q. Niu, Physical Review Letters 112, 085503 (2014). They show how it enters the problem of the relaxation of the atomic spin in the elastic body and explicitly demonstrate the conservation of the total angular momentum in spin-phonon processes at the microscopic level.

[Phys. Rev. B 92, 024421] Published Mon Jul 20, 2015

]]>Measurements of thermal and electrical transport at low temperature near an unconventional quantum critical point in $\beta $-YbAlB${}_{4}$ reveal that the Wiedemann-Franz law continues to be obeyed and Landau quasiparticles remain intact.

[Phys. Rev. B 92, 041114(R)] Published Mon Jul 20, 2015

]]>The authors report observation of extremely large magnetoresistance in two compounds which were recently suggested as candidates for Weyl semimetals.

[Phys. Rev. B 92, 041203(R)] Published Mon Jul 20, 2015

]]>The traditional methods for manipulating the magnetization precession resonantly by microwaves fail to operate at the nanoscale. In the present paper, by using a specially designed ferromagnetic structure, the authors demonstrate resonant driving of the magnetization precession at microwave frequencies by exploiting coherent lattice vibrations. They use a 59-nm ferromagnetic layer as cavity of a phononic Fabry-Perot nanoresonator formed by a semiconductor superlattice. The coherent phonons with resonance frequencies up to 30 GHz are excited by femtosecond laser pulses and feed the magnetization precession within their nanosecond lifetime. The amplitude of the precession increases drastically for resonant conditions when the frequency of the free precession is equal to the frequency of the driving magnetostrictive force.

[Phys. Rev. B 92, 020404(R)] Published Thu Jul 16, 2015

]]>The critical behavior of quantum Hall transitions in two-dimensional disordered electronic systems can be described by a class of non-unitary conformal field theories with logarithmic correlations. Using the replica trick and the underlying symmetries of these quantum critical points, the author shows how to construct non-perturbatively disorder-averaged observables in terms of Green’s functions that scale logarithmically at criticality.

[Phys. Rev. B 92, 014205] Published Wed Jul 15, 2015

]]>The new family of layered organic-inorganic perovskite crystals (OIPCs) is a unique addition to the set of available 2D materials. It is a crystalline inorganic solid that is surrounded by well-ordered organic ligands, both of which can be modified separately. This hybrid character endows the material with an unusual degree of tunability and flexibility. Here, the authors present their results on the synthesis and extensive characterization of 2D OIPC single-crystalline bilayers of (C${}_{4}$H${}_{9}$NH${}_{3}$)${}_{2}$PbI${}_{4}$. These materials could significantly expand the range of van der Waals heterostructures that can be produced by their combination with, e.g., graphene, $h$-BN layers, transition metal dichalcogenide layers, etc.

[Phys. Rev. B 92, 045414] Published Tue Jul 14, 2015

]]>Renormalization group analysis of the effects of disorder and interactions in two-dimensions shows that in some parameter regimes superconductivity can even be enhanced by localization effects.

[Phys. Rev. B 92, 014506] Published Mon Jul 13, 2015

]]>Nontrivial (hidden) symmetries present within extended Kitaev-Heisenberg model, have been recently introduced to capture the magnetism of layered honeycomb iridates Na${}_{2}$IrO${}_{3}$ and Li${}_{2}$IrO${}_{3}$. The authors study the hidden symmetries of a generic four-parameter nearest-neighbor spin model of iridates of the ${A}_{2}$IrO${}_{3}$ kind in the honeycomb lattice compounds under trigonal compression. Their method utilizes a mapping of the Hamiltonian on itself by using the symmetry of the Hamiltonian, which connects different points in its parameter space. They claim that a complete set of points of hidden SU(2) symmetry at which seemingly highly anisotropic model can be mapped back on the Heisenberg model and inherits therefore its properties such as the presence of gapless Goldstone modes.

[Phys. Rev. B 92, 024413] Published Mon Jul 13, 2015

]]>The interplay between superconductivity and magnetism is a complex but very interesting and technologically important topic in solid state physics. The rich physics resulting from the competition of these two phases has been studied so far with models and phenomenological approaches that leave the prediction of material-specific properties, such as the critical temperature ${T}_{c}$, or the magnetization, out of reach. Density functional approaches have been very successful in the prediction of the material specific magnetization via Spin-DFT on the one, and Tc for superconducting system via SCDFT on the other hand. In this work the authors present a fully $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ theory to describe the microscopic competition of magnetism and superconductivity, in the framework of a density functional theory unifying SpinDFT and SCDFT.

[Phys. Rev. B 92, 024505] Published Wed Jul 08, 2015

]]>This work presents the numerical solution of the equations derived in the companion manuscript “$A\phantom{\rule{0}{0ex}}b$ $I\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ Theory of Superconductivity in a Magnetic Field. I. Spin Density Functional Theory For Superconductors and Eliashberg Equations.” and the comparison of the methods presented therein. To perform this comparison the authors analyze a superconducting test system where free electron states couple via a phonon field and are Zeeman split by a tunable homogeneous magnetic field. It turns out that while the superconducting analogue of the Kohn-Sham (KS) density functional framework can accurately predict the superconducting critical temperature, it also suffers from the analogue of the “band gap” problem for the quasiparticle spectrum in the superconducting state. The authors resolve this problem by introducing a generalization of the ${G}_{0}$${W}_{0}$ approximation to superconductors.

[Phys. Rev. B 92, 024506] Published Wed Jul 08, 2015

]]>Motivated by the question of whether or not two gapped Hamiltonians belong to the same phase, the authors compare two exactly solvable lattice models. They show that the only way to see that these models belong to distinct phases is to examine their three-loop braiding statistics.

[Phys. Rev. B 92, 035115] Published Wed Jul 08, 2015

]]>Angle-resolved photoemission shows the existence of two-dimensional metallic states of confined itinerant electrons at the (001) and (101) surfaces of insulating TiO${}_{2}$ anatase. This is a material of much current interest, as a photocatalyst or a transparent conducting oxide, for instance. The 2D electron gases come from the formation of oxygen vacancies in the near-surface region, created by exposure to ultraviolet irradiation. The results here open a route to nano-engineering these confined electronic states using ultraviolet light, controlling their metallic or insulating nature.

[Phys. Rev. B 92, 041106(R)] Published Wed Jul 08, 2015

]]>It was reported earlier that alkali metal doped picene shows superconductivity at rather high temperatures. In this paper the authors have prepared such materials and thoroughly analyzed them using a variety of measurements. They conclude that superconductivity in doped hydrocarbons is questionable, casting doubts on the previous interpretation of the data.

[Phys. Rev. B 92, 014502] Published Tue Jul 07, 2015

]]>Sr${}_{3}$Ir${}_{2}$O${}_{7}$ is a member of the iridate Ruddlesden-Popper series Sr${}_{n+1}$Ir${}_{n}$O${}_{3n+1}$ with electronic properties that interpolate between the insulating single-layer Sr${}_{2}$IrO${}_{4}$ ($n=1$) and a metallic compound SrIrO${}_{3}$ ($n=\mathrm{\infty}$). Using resonant inelastic X-ray scattering (RIXS) experiments, the authors reveal a new magnetic mode and propose a model based on weakly coupled quantum dimers to describe the observed excitation spectrum.

[Phys. Rev. B 92, 024405] Published Mon Jul 06, 2015

]]>The authors study magneto-electric properties of several hexagonal manganites and ferrites (HoMnO${}_{3}$, ErMnO${}_{3}$, YbMnO${}_{3}$, LuMnO${}_{3}$, and LuFeO${}_{3}$). By disentangling the contributions of exchange striction and the spin-orbit coupling, they propose HoMnO${}_{3}$ as a promising candidate material with magneto-electric coefficient reaching 15 ps/m.

[Phys. Rev. B 92, 035107] Published Mon Jul 06, 2015

]]>The authors study a generic quantum dot close to the particle-hole symmetric point. By first mapping the model onto an equivalent two-level system coupled to spin-polarized leads, they are able to study the system as a function of magnetic field at large bias voltage. Doing so they are able to identify a non-equilibrium fixed point of the model.

[Phys. Rev. B 92, 041103(R)] Published Mon Jul 06, 2015

]]>The tungsten ditelluride WTe${}_{2}$ semimetal is known for if its extremely large magnetoresistance. The authors measure the angular dependence of this magnetoresistance and find that when the magnetic field is applied parallel to the tungsten chains (along the $a$ axis), the very large magnetoresistance (as high as 1200% at 15 T and 2 K) no longer exhibits a conventional quadratic but rather a linear field dependence.

[Phys. Rev. B 92, 041104(R)] Published Mon Jul 06, 2015

]]>The study of Raman scattering processes in the ultraviolet excitation energy range is not common in carbon-based materials. This paper reports that the widely known double-resonant Raman scattering, which is dominant in the visible excitation energy in these materials, is suppressed in the UV range. This is an important development because one can now measure two-phonon densities of states that were not accessible before. The results demonstrate the high potential of UV Raman spectroscopy for research on graphitic nanocarbons.

[Phys. Rev. B 92, 041401(R)] Published Wed Jul 01, 2015

]]>While efficient algorithms exist for the simulation of bosons simulations of fermions are more challenging because of the infamous fermion sign problem. In this paper the authors take a step toward solution and develop continuous-time quantum Monte Carlo algorithm for lattice fermions that scales linearly with projection time and interaction strength. This method is benchmarked on the problem of the fermionic quantum critical point of spinless fermions on a honeycomb lattice.

[Phys. Rev. B 91, 235151] Published Tue Jun 30, 2015

]]>Much attention has been devoted recently to identify possible ways to overcome the notorious sign problem encountered in quantum Monte Carlo simulations. The authors of this paper propose a new method based on Majorana representation of complex fermions, which they dub Majorana Quantum Monte Carlo (MQMC). They find a class of SU(N) fermionic models which are sign-free in MQMC but cannot be solved with other available methods.

[Phys. Rev. B 91, 241117(R)] Published Tue Jun 30, 2015

]]>Nonsymmorphic materials, which possess special symmetry operations (screw rotation, glide mirror), have been theoretically reexamined in recent years for possible novel quantum phases or electronic functions derived from the symmetry requirements. Here, the authors demonstrate that in the typical nonsymmorphic material IrO${}_{2}$, the type of charge carrier (electron or hole) is strongly dependent on the crystal orientation and capable of being switched by a magnetic field. This remarkable effect is seen in electrical transport measurements on various thin films supported by simple tight-binding and band structure calculations.

[Phys. Rev. B 91, 241119(R)] Published Tue Jun 30, 2015

]]>Dislocations are central to the understanding of plasticity in metals. Using density functional theory the authors show that interstitial carbon atoms in ferritic steels stabilize a dislocation core configuration called a hard core which is otherwise unstable. Since, as they also show, at equilibrium all dislocations are expected to be fully decorated by carbon atoms, this has important implications for the understanding of plasticity in ferritic steels. It is expected that the picture developed here could also be applicable to other solutes besides carbon and to other metals besides iron.

[Phys. Rev. B 91, 220102(R)] Published Mon Jun 29, 2015

]]>Infrared spectroscopy of VO${}_{2}$ thin films at high spatial resolution shows new electronic and lattice states due to epitaxial strain that differ fundamentally from those in the bulk. This is the first ultra-broadband infrared near-field study of a correlated electron material, made possible by the newly developed synchrotron infrared near-field spectroscopy method (SINS) on the Advanced Light Source at Lawrence Berkeley National Laboratory.

[Phys. Rev. B 91, 245155] Published Mon Jun 29, 2015

]]>The authors study the proton correlations present in water ice in its ice rule phase ${I}_{h}$. Using an effective field theory, an analytic form for the correlation function is derived and then compared against numerics, showing excellent agreement. This field theory is argued to be a U(1) gauge theory in its deconfined Coulomb phase.

[Phys. Rev. B 91, 245152] Published Thu Jun 25, 2015

]]>The formation of extended electron states in one-dimensional nanostructures is of key importance for the function of molecular electronics devices. In this paper, using a combination of atomic force microscopy, scanning tunneling spectroscopy, and tight-binding calculations the authors investigate the confinement of electronic states to controlled Cl vacancy pairs in a NaCl bilayer on Cu(111). They reveal that electron-phonon coupling has great influence on these quantities.

[Phys. Rev. B 91, 235443] Published Wed Jun 24, 2015

]]>Can the two-dimensional interaction driven Mott metal-insulator transition be continuous? Motivated by experiments on quasi two-dimensional organics that may show such a transition the authors study a two-leg triangular Hubbard strip. They argue that this model harbors a continuous Kosterlitz-Thouless-like quantum phase transition between a metal and a gapless spin liquid.

[Phys. Rev. B 91, 235140] Published Tue Jun 23, 2015

]]>A theoretical formalism is developed to calculate the optical force induced within a 2D metamaterial, based on the electrostrictive tensor. It turns out that it is not always straightforward to use the usual effective-medium parameters $\u03f5$ and $\mu $ of the metamaterial for obtaining the body force density. The findings are tested via a 2D array of parallel infinitely long dielectric cylinders and the analytical theory is in excellent agreement with numerics. The correct stress tensor to describe the force density in an effective medium is the Helmholtz one rather than the Maxwell. The theory, though, is not exact and points to a fundamental limitation of effective medium theory in describing light-induced body forces.

[Phys. Rev. B 91, 235439] Published Tue Jun 23, 2015

]]>Polar zinc titanate (ZnTiO${}_{3}$) is a promising lead-free ferroelectric compound with high spontaneous polarization of 75 $\mu \phantom{\rule{0}{0ex}}C/c\phantom{\rule{0}{0ex}}{m}^{2}$, which is comparable with that of PbTiO${}_{3}$. In this work a collaboration of researchers from Germany, UK, and USA present a detailed investigation of vibrational properties of ZnTiO${}_{3}$ via the high-pressure Raman spectroscopy, second-harmonic generation, and $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations.

[Phys. Rev. B 91, 214110] Published Mon Jun 22, 2015

]]>Thorough experimental investigations from this group provide new data and cogent understanding of the effects of copper substitution in iron telluride over a broad substitution range. They also show how subtle changes in copper substitution and an applied magnetic field modify the low-temperature magnetic and structural phases in these materials, as well as the nature of the transitions into these phases.

[Phys. Rev. B 91, 224424] Published Mon Jun 22, 2015

]]>Using broadband spectroscopic ellipsometry, the authors determine the complex valued dielectric function of silver films from 0.05 eV (λ=25 μ) to 4.14 eV (λ = 300 nm) with a statistical uncertainty of less than 1%. While several previous similar measurements exist, they span considerably shorter energy ranges and report partially inconsistent results. In view of the wide-ranging applications of silver in nanophotonics, plasmonics and optical metamaterials, we anticipate this paper to become a standard reference for many scientists and engineers.

[Phys. Rev. B 91, 235137] Published Mon Jun 22, 2015

]]>This works brings us a step closer towards the realization of the quantum spin Hall (QSH) effect. Using electronic structure calculations, the authors suggest that a family of the single-layer 2D transition metal dichalcogenide haeckelites $M\phantom{\rule{0}{0ex}}{X}_{2}$ ($M$=W or Mo, $X$=S, Se, or Te) can host the QSH effect at high temperatures. Their work also implies that a square-lattice 2D material can host a nontrivial topological state, thus, extending the search boundaries for topological materials beyond the ones with a hexagonal lattice.

[Phys. Rev. B 91, 235434] Published Fri Jun 19, 2015

]]>Experimental measurement of topological degeneracy of fractional quantum Hall states is obstructed by the requirement of a torus geometry. The authors propose an alternative scheme which relies on the realization of ground state degeneracy in an effective torus geometry. It is achieved by gluing the edges of a bilayer annulus, where the layers are occupied by electron and hole fractional quantum Hall states or by a topological insulator.

[Phys. Rev. B 91, 245144] Published Fri Jun 19, 2015

]]>In quantum mechanics, weak measurement allows one to measure off diagonal matrix elements of operators. In this work, the author designs a weak value protocol which can be harnessed to measure the topological invariant of a quantum spin Hall insulator.

[Phys. Rev. B 91, 241109(R)] Published Thu Jun 18, 2015

]]>Recently D. I. Khomskii proposed that the elementary excitations in spin ice materials, the magnetic monopoles, also possess electric dipole moments. In this manuscript the properties of such magneto-electric monopoles are explored within a model of spin ice materials that includes nearest-neighbour coupling, Zeeman energy, electric and magnetic dipolar interactions, with a particular emphasis on a prototype spin-liquid pyrochlore Tb${}_{2}$Ti${}_{2}$O${}_{7}$.

[Phys. Rev. B 91, 214422] Published Wed Jun 17, 2015

]]>A single unit cell FeTe${}_{1-x}$Se${}_{x}$ film consisting of a flat square Fe layer sandwiched between two Se/Te monolayers shows a fully gapped tunneling spectrum with superconducting gaps up to ~16.5 meV, nearly ten times the gap value of an optimally doped bulk single crystal. Compared with the ${T}_{c}$~14.5 K of bulk FeTe${}_{0.6}$Se${}_{0.4}$, a gap of ~16.5 meV could correspond to a transition temperature higher than the boiling temperature of liquid-nitrogen (77 K). Initial $e\phantom{\rule{0}{0ex}}x$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ transport measurements reveal an onset superconducting transition temperature above 40 K, nearly two times higher than that of the optimally doped bulk single crystal FeTe${}_{0.6}$Se${}_{0.4}$.

[Phys. Rev. B 91, 220503(R)] Published Wed Jun 17, 2015

]]>Fe atoms adsorbed on Cu(111) have been used as an atomic-scale model system for performing spin-based logic operations and to build the smallest stable magnet. In pursuit of understanding the strength of the adatom/substrate hybridization in this system, small Fe clusters down to single atoms adsorbed on a Cu(111) surface were studied using X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism experiments. The spin and orbital moments as well as the magnetic anisotropy energies were extracted experimentally and compared with density functional theory and multiplet calculations. The results show an unexpectedly sharp atomic-like multiplet feature for single Fe atoms which disappears with increasing coverage and cluster size. This indicates a surprisingly weak hybridization of the Fe 3d states to the electronic states of the Cu(111) substrate.

[Phys. Rev. B 91, 235426] Published Tue Jun 16, 2015

]]>In this paper the authors study the dependence of the visibility of the Aharonov-Bohm oscillations of an electronic Mach-Zehnder interferometer upon the transmission properties of an additional quantum point contact placed in front of the interferometer’s input. According to a theory by I. P. Levkivskyi and E. V. Sukhorukov ( Phys. Rev. Lett. 103, 036801 (2009)), a non-equilibrium noise-induced phase transition is meant to occur when the transmission of the point contact equals 1/2. The authors present experimental evidence for the existence of this critical point.

[Phys. Rev. B 91, 245419] Published Tue Jun 16, 2015

]]>The authors show theoretically that hyperbolic metasurfaces support simultaneous propagation of both quasi-TE and quasi-TM plasmon surface modes of “hybrid’” polarization at the same frequency — a two-dimensional analog of D’yakonov surface waves. The shape of their equal-frequency contours depends drastically on the frequency and changes from elliptical to hyperbolic, and so a topological transition takes place.

[Phys. Rev. B 91, 235423] Published Mon Jun 15, 2015

]]>Measurements of thermoelectric power are used to show that the heavy fermion compound CeRh${}_{2}$Si${}_{2}$ has very different Fermi surfaces in different portions of the pressure-temperature phase diagram.

[Phys. Rev. B 91, 245129] Published Mon Jun 15, 2015

]]>Angle-resolved photoemission spectroscopy experiments reveal that the valence band splitting at $K$ point in transition metal dichalcogenides is primarily due to the spin-orbit coupling rather than inter-layer interactions. The authors have achieved convincing agreement between experimental results and theoretical calculations over a wide energy range.

[Phys. Rev. B 91, 235202] Published Thu Jun 11, 2015

]]>In this paper, the authors study the entanglement between two quantum dots mediated by a superconducting island hosting a pair of Majorana bound states. They show that, within several parameter regions, it is possible to obtain long-ranged entanglement between the dots and study the degree of this entanglement after a quench of tunnel couplings to the dots.

[Phys. Rev. B 91, 214507] Published Wed Jun 10, 2015

]]>Entanglement entropy in several quantum impurity models is computed around the quantum critical point between the ordered and disordered phases and is found to be non-universal.

[Phys. Rev. B 91, 245122] Published Wed Jun 10, 2015

]]>Using a cleverly designed device contacting superconducting leads to a carbon nanotube quantum dot, the authors investigate the magnetic state of a quantum dot attached to superconducting leads in a regime where the Kondo energy competes with the superconducting correlations. In this regime, the magnetic state of the system depends on the difference of superconducting phase between the two electrodes. This paper reports the first experimental observation of this effect.

[Phys. Rev. B 91, 241401(R)] Published Tue Jun 09, 2015

]]>In this work the authors generate the ten-fold classification of the periodic table of topological insulators by studying random Dirac Hamiltonians supporting a Dirac mass. They use homotopy groups to establish the phase diagram that encodes Anderson localization and provide an alternative explanation for the even-odd effect in the one-dimensional chiral classes.

[Phys. Rev. B 91, 235111] Published Mon Jun 08, 2015

]]>Coupling arrays of extrinsic defects provides a promising avenue towards realizing exotic phases of matter. By varying the coupling between parafermionic zero modes and moving from triangular lattice to square lattice authors explore the ground states of the model and describe a method to assemble Fibonacci anyons.

[Phys. Rev. B 91, 235112] Published Mon Jun 08, 2015

]]>Two new first-order Raman-active modes are experimentally observed in few-layer MoS${}_{2}$ samples. The authors of this paper show that these modes should appear in virtually all few-layer systems. Since these new modes are symmetry-forbidden in single-layer structures, the results are going to be useful for metrology of layered thin films.

[Phys. Rev. B 91, 235409] Published Mon Jun 08, 2015

]]>While many of the effects in two-dimensional topological insulators do not depend on the precise edge state structure because of their topological nature, more detailed experimental probes can extract non-topological information. In this paper the authors present comprehensive study of helical edge states of generic quantum spin Hall insulators whose quantization axis rotates as a function of the edge carrier momentum. This analysis reveals the information that can aid the spectroscopic detection of the spin texture of helical edge states.

[Phys. Rev. B 91, 245112] Published Mon Jun 08, 2015

]]>In this proof-of-concept analytical study (supported by numerical examples) the authors are able to achieve controllable enhancement of the electrostriction in a metamaterial medium consisting of an array of spheres in a host medium. Accounting for material dispersion and losses for a few test cases, they show a sizable enhancement (or suppression) and tunability of the electrostrictive properties. We anticipate that this study will open interesting directions previously unexplored in metamaterials research.

[Phys. Rev. B 91, 214102] Published Thu Jun 04, 2015

]]>A method is proposed to solve a longstanding problem in photoelectron spectroscopy: the determination of the branching ratio between intrinsic and extrinsic plasmon generation. Attosecond metrology in combination with model simulations allow for a disentanglement of these excitation channels providing novel insight into the many-electron response of metals.

[Phys. Rev. B 91, 241101(R)] Published Wed Jun 03, 2015

]]>A magnetic insulator, LiInCr${}_{4}$O${}_{8}$ realizes a so-called “breathing” pyrochlore lattice of $S=3/2$ spins on corner-sharing tetrahedra that alternate in size. In this manuscript, a collaboration of researchers from Institut Laue-Langevin in Grenoble and Institute for Solid State Physics in Tokyo present a detailed neutron scattering study that elucidates the sequence of structural and magnetic phase transitions that occur at low temperatures in this material.

[Phys. Rev. B 91, 174435] Published Wed May 27, 2015

]]>Nonradiative deep level carrier trapping, also known as the Shockley-Read-Hall effect, is an old and important problem in semiconductor physics. Five different possible formalisms, which have given very different results for calculations of the capture coefficients, are compared here with each other and with extant experimental results for two complex defect structures: GaP:Zn${}_{G\phantom{\rule{0}{0ex}}a}$-O${}_{P}$ and GaN:Zn${}_{G\phantom{\rule{0}{0ex}}a}$-V${}_{N}$. The static coupling theory is shown to be in the best agreement with experiment and arguments are provided for why it should be used in calculations of nonradiative carrier recombination.

[Phys. Rev. B 91, 205315] Published Wed May 27, 2015

]]>A single artificial atom maser can be realized using a superconducting single electron transistor coupled to an oscillator or a double dot coupled to a transmission-line resonator. The authors suggest a model to describe the possibility of lasing action in various environments under different coupling mechanism.

[Phys. Rev. B 91, 184515] Published Tue May 26, 2015

]]>In this study of non-equilibrium heat transport in quantum nanostructures as modeled by the Anderson impurity model, the authors show that monitoring the energy conductance as a function of gate or source-drain voltage can reveal the fingerprints of inelastic scattering processes in a way that the charge conductance does not.

[Phys. Rev. B 91, 201107(R)] Published Tue May 26, 2015

]]>Wannier functions are an important and practical tool to simplify electronic structure calculations used to compute various physical properties. However, in cases of multi-parameter Hamiltonians, several sets of Wannier functions are required, making the computation often prohibitive. The authors have found a solution to this with a formalism that instead allows computation of a single parameter-dependent set of higher-dimensional Wannier functions (HDWFs). This formalism is demonstrated using toy models that show it can be applied to a variety of problems such as the virtual crystal approximation of disorder, ferroelectric polarization, and spin torques.

[Phys. Rev. B 91, 184413] Published Thu May 21, 2015

]]>A natural place to look for symmetry protected topological phases in three dimensions are magnetic models built from spin-1. As an example, the authors consider an AKLT-derived loop model of spin-1’s on a diamond lattice.

[Phys. Rev. B 91, 195131] Published Wed May 20, 2015

]]>On the basis of novel insight in the physics of Majorana modes, the authors solve the microscopic mechanism of the anomalous proximity effect and propose an experimental setup for its observation.

[Phys. Rev. B 91, 174511] Published Fri May 15, 2015

]]>The overheating of microprocessors components is currently the most limiting factor in the development of information technology. This motivates the concern in finding innovative ways to control and evacuate heat in nanoscale devices. In the presence of a magnetic field B, the heat currents flowing through a generic setup exhibit reversible and irreversible components: the former are reversed when inverting B→-B, whereas the latter remain unchanged. In this work the authors exploit this feature to propose a magnetic thermal switch: a setup which allows control of the heat flow by making use of an external magnetic field as a selector of a desired working configuration. Several features, like switching on/off, inversion, partition and swap of the heat currents, can be implemented in a programmable device allowing full controllability. Among the advantages of this approach are the absence of any temperature constraints and the possibility to control phononic, in addition to electronic, heat flows.

[Phys. Rev. B 91, 205420] Published Thu May 14, 2015

]]>Mesoscopic circuits can be coupled to microwave cavities to form hybrid light-matter systems. This emerging field represents an intermediate regime between standard cavity and circuit quantum electrodynamics. In this paper, the authors develop a general method based on a photonic pseudo-potential to describe the electric coupling between electrons in a nanocircuit and cavity photons.

[Phys. Rev. B 91, 205417] Published Wed May 13, 2015

]]>Topological phases of matter lack conventional local order parameter but might have hidden orders. This is exemplified by quantum Hall states for which Laughlin’s wavefunction approach revealed a connection between topological phases and broken symmetry. The authors utilize this approach to construct candidate wave functions for one- and two-dimensional symmetry-protected phases (SPT) and provide evidence that their candidate states do in fact belong to SPT.

[Phys. Rev. B 91, 195117] Published Tue May 12, 2015

]]>This is a comprehensive Raman scattering study of electrochemically gated graphene transistors. A robust, highly accurate determination of the Fermi level, electron-phonon coupling, and defect scattering rates is achieved. Fermi energies as high as 700 meV above the Dirac point were achieved in ambient conditions, without damaging graphene. This opens exciting perspectives for optoelectronics.

[Phys. Rev. B 91, 205413] Published Tue May 12, 2015

]]>Authors observe a new magnetoresistance phenomenon in a relativistic structure which allows them to detect a 180 degrees magnetization reversal without breaking the symmetry between the two states by a magnetic field or a reference ferromagnet.

[Phys. Rev. B 91, 180402(R)] Published Mon May 11, 2015

]]>Theoretical predictions and experimental results demonstrate that mu-near zero metamaterials allow enhanced transmission (supercoupling) between two waveguides coupled by a channel with a disproportionately wide cross section. This effect is related but distinctly different from (and cannot be reduced to) a previously reported supercoupling effect using epsilon-near-zero metamaterials.

[Phys. Rev. B 91, 195112] Published Mon May 11, 2015

]]>Requirement of adiabaticity in the process of braiding of Majorana modes presents serious challenges to its practical implementation. The authors explore how to minimize nonadiabatic errors for finite braiding times by finding an optimal protocol for the Majorana movement. They show, counterintuitively, that protocols characterized by sharp transitions between Majorana motion at maximal and minimal velocities may do the trick.

[Phys. Rev. B 91, 201404(R)] Published Mon May 11, 2015

]]>Motivated by the appearance of optically induced superconductivity in the stripe-ordered La${}_{1.885}$Ba${}_{0.115}$CuO${}_{4}$ cuprate, this group uses time-resolved THz spectroscopy to map out the enhancement of interlayer superconducting coupling as a function of both temperature and time delay, for different pump wavelengths and fluences.

[Phys. Rev. B 91, 174502] Published Tue May 05, 2015

]]>Electrochemical doping in 2D transition-metal dichalcogenides (TDMs) aimed at creating field effect transistor (FET) conditions can allow one to explore interesting transport phenomena in reduced dimensionality. In this timely work, the authors thoroughly investigate from first principles how field-effect doping affects the structural properties, electronic structure, and Hall coefficient of mono- and few-layers TDMs. They show that (i) the models, typically, used to estimate the doping charge in FET devices cannot be applied to 2D TMDs and, (ii) given the multivalley nature of both the conduction and valence bands, small differences in the band structure can manifest in transport behavior that is very different from that predicted based on a single parabolic band.

[Phys. Rev. B 91, 155436] Published Thu Apr 30, 2015

]]>Can topologically non-trivial states, such as those in topological insulators and superconductors, arise in the mixed states of open quantum systems? By imposing special constraints on the gauge structure of the density matrices which describe open quantum systems, the authors find non-trivial topological invariants showing that topological phenomena can be generalized to mixed states. The method is illustrated with an analysis of Chern insulators at finite temperature.

[Phys. Rev. B 91, 165140] Published Thu Apr 30, 2015

]]>The paper reports the observation of an anisotropic capacitance in a parallel plate $p$-$n$ junction capacitor where one plate is a ferromagnetic semiconductor, GaMnAs, and the other is nonmagnetic $n$-doped GaAs. The capacitance depends on the angle of the magnetization of the ferromagnetic plate and is analogous to the tunneling anisotropic magnetoresistance, which originates from the spin-orbit interaction. This can be an important effect in magnetic sensor applications.

[Phys. Rev. B 91, 140409(R)] Published Wed Apr 29, 2015

]]>This paper reports on the experimental and theoretical investigation of nonequilibrium Kondo effect in carbon nanotube quantum dots. At low temperature and in the absence of magnetic field, the authors observe two symmetric satellite features on either side of the zero bias peak due to the splitting of single-particle states by the spin-orbit coupling and valley mixing. Further experimental results are discussed based on the underlying symmetries of the carbon nanotube energy spectrum.

[Phys. Rev. B 91, 155435] Published Wed Apr 29, 2015

]]>The authors consider the phenomena of quantum revivals in a system exhibiting many-body localization. To this end the authors study a qubit attached to a disordered insulator. Without interactions, the qubit undergoes revivals at a rate that approaches a constant as time goes to infinity. If interactions are added to the insulator, this rate sees instead a logarithmic suppression in time. This logarithmic behavior is related to the same mechanism that underpins the logarithmic growth in entanglement entropy after a quantum quench in a many-body localized system.

[Phys. Rev. B 91, 140202(R)] Published Mon Apr 27, 2015

]]>Inelastic scattering of electrons on crystals can excite lattice vibrations known as phonons. An energy resolution of 10 meV in the scattered electron energy loss has recently been demonstrated in scanning transmission electron microscopy (STEM), permitting experimenters to distinguish between elastic and inelastic scattering events. In this paper the authors present simulations showing that, with the recent improvement in energy resolution, atomic resolution phonon spectroscopy and imaging of crystals using STEM should now be feasible.

[Phys. Rev. B 91, 144108] Published Mon Apr 20, 2015

]]>Cu${}_{x}$Bi${}_{2}$Se${}_{3}$ is a material of significant recent interest and controversy, as it might be a topological superconductor. However, it is now apparent that different preparation routes yield crystals with different properties. This group offers the first systematic study of the preparation-dependence of superconductivity in this material.

[Phys. Rev. B 91, 144506] Published Mon Apr 20, 2015

]]>The topological central charge is a property that takes the same value throughout a topological phase of matter. In this work authors show how to compute topological central charge as a Berry curvature associated with position-dependent changes in the spatial metric in the bulk of the system.

[Phys. Rev. B 91, 165306] Published Mon Apr 20, 2015

]]>According to a recent theoretical conjecture for a classification of symmetry protected topological (SPT) phases which can arise in a collection of lattice boson models called group cohomology models, each model belongs to a distinct SPT phase, and each SPT phase can be realized by a model. Here the authors show that for SPT phases with symmetry groups that are finite, Abelian, and unitary, each group cohomology model can be characterized by a unique set of topological invariants and therefore belongs to a distinct SPT phase. In two dimensions it is further shown that the complete set of group cohomology models accounts for all SPT phases, while in three dimensions evidence pointing toward such a proof is found.

[Phys. Rev. B 91, 165119] Published Wed Apr 15, 2015

]]>Near-field electromagnetic heat transfer is studied in a theoretical semiconductor heterojunction system in the presence of a non-zero chemical potential (via a bias voltage). Changing the potential enables electronic control of near-field heat transfer and suggests a novel and very exciting new possibility for achieving solid-state cooling, a holy grail in thermal science.

[Phys. Rev. B 91, 134301] Published Mon Apr 13, 2015

]]>Synthesis of a new material in the iridate family with a continuously tunable valence of Ir shows the dominant role played by spin-orbit coupling in determining the magnetic properties.

[Phys. Rev. B 91, 155117] Published Mon Apr 13, 2015

]]>The much debated topology of Bi${}_{1-x}$Sb${}_{x}$ has been resolved in this very careful and thorough experiment. The authors optimized the Bi${}_{1-x}$Sb${}_{x}$ growth method and minimized surface imperfections. They performed direct measurements of the surface band structure and followed its evolution within a large window of Sb concentration. They did not detect a third surface band seen in previous experiments. Thus, they conclude that the experimental surface band structure of B${}_{1-x}$Sb${}_{x}$ in the topologically insulating regime now agrees well with the theoretical predictions.

[Phys. Rev. B 91, 161406(R)] Published Mon Apr 13, 2015

]]>Using high resolution THz spectroscopy, the authors study spinon confinement in the weakly coupled antiferromagnetic chain compound SrCo${}_{2}$V${}_{2}$O${}_{8}$. The confined spinons appear in a hierarchy that can be fully described by a one dimensional Schrödinger equation with a linear confinement potential.

[Phys. Rev. B 91, 140404(R)] Published Thu Apr 09, 2015

]]>In addition to its extraordinary mechanical, thermal and electrical properties, graphene shows great potential in manipulating electromagnetic fields. One of the main advantages of graphene compared to other materials is the extraordinary tunability of its conductivity, which can be achieved electrically by means of a back gate, or optically through the excitation of photocarriers. Scientists from Belgium, Sweden and the United States demonstrate that this tunability of graphene can be used in a novel setup for the generation of frequency combs. Traditionally, frequency combs are generated using nonlinear materials. The researchers studied the interaction between light and time-dependent graphene sheets, including both dispersion and explicit time-dependence of the conductivity. Based on this model, they demonstrated that frequency combs can be generated without material nonlinearities. Indeed, at terahertz frequencies it is possible to modulate the linear, time-dependent conductivity of graphene to obtain a large variety of frequency combs.

[Phys. Rev. B 91, 161403(R)] Published Wed Apr 08, 2015

]]>Motivated by recent measurements of state-selective intersystem crossing (ISC) in the nitrogen-vacancy (NV) center in diamond (see companion PRL), a new microscopic model is developed of the key ISC mechanism. These nonradiative transitions between states of different spin multiplicity are pivotal in the optical initialization and readout of the NV center’s electronic spin, which has created a diverse range of room-temperature applications in metrology and quantum information science.

[Phys. Rev. B 91, 165201] Published Wed Apr 08, 2015

]]>Improvements in experimental resolution allow this group to elucidate how the electronic nematic transition evolves in FeSe. They observe the changing Fermi surface, the position of the lowest energy electronic excitations, as well as the propensity towards nematic order and its manifestation under strain.

[Phys. Rev. B 91, 155106] Published Tue Apr 07, 2015

]]>Using semiclassical nonlinear sigma model techniques the authors classify a broad class of bosonic symmetry protected topological phases. This construction works in all dimensions.

[Phys. Rev. B 91, 134404] Published Mon Apr 06, 2015

]]>Diluted magnetic semiconductors have attracted much attention as candidates for spintronic devices after the discovery of ferromagnetism in Mn-doped GaAs. However, the limited chemical solubility of the magnetic element Mn together with the inability to control carrier density independently of the magnetic element concentration are major obstacles to material design and applications. The newly found diluted magnetic semiconductor Ba${}_{1-y}$K${}_{y}$(Zn${}_{1-x}$Mn${}_{x}$)${}_{2}$As${}_{2}$, which has the same crystal structure as the iron-based superconductor BaFe${}_{2}$As${}_{2}$, circumvents these problems and exhibits ferromagnetic transition temperatures as high as 230 K. Using x-ray absorption and resonance photoemission spectroscopy this group explicitly demonstrates that the ThCr${}_{2}$Si${}_{2}$-type crystal structure is an ideal framework both for high-temperature superconductivity and for ferromagnetism, and that the carrier-induced ferromagnetism of GaMnAs is operating in other ferromagnetic semiconductors.

[Phys. Rev. B 91, 140401(R)] Published Mon Apr 06, 2015

]]>First-principles calculations presented in this Rapid Communication suggest that a number of $A\phantom{\rule{0}{0ex}}B$ binary honeycomb monolayers should be ferroelectric. Dipoles arise from the buckled structure, and the polarization reversal occurs via switching the structural buckling which can be triggered by an external electric field. The authors address the emerging valley-dependent properties arising from the ferroelectric bistability and explore the intimate link between ferroelectricity, spin-valley physics, and Rashba spin-splitting phenomena.

[Phys. Rev. B 91, 161401(R)] Published Mon Apr 06, 2015

]]>Most of the previously suggested scenarios for the realization of Weyl semimetal on a pyrochlore lattice require breaking of time-reversal symmetry. In this study the authors show that spontaneous deformations of the crystal that break the inversion symmetry can stabilize this phase as well. They demonstrate that in the temperature-elasticity phase diagram Weyl semimetal shows a reentrant behavior.

[Phys. Rev. B 91, 165105] Published Mon Apr 06, 2015

]]>Semiconductor nanostructures, such as arrays of Si nanowires, are promising candidates for photonic and photovoltaic applications where light management and light trapping abilities are essential. A significant aspect for the development of such functionality is understanding the electromagnetic field distribution around the nanostructures. In this Rapid Communication, a collaboration of researchers from Toulouse and Grenoble use nonlinear microscopy on isolated silicon nanowires in order to study the local electromagnetic field morphology. They find that the second harmonic generation yield in Si nanowires can be strongly enhanced compared to bulk silicon.

[Phys. Rev. B 91, 121416(R)] Published Tue Mar 31, 2015

]]>Density functional theory calculations of the electronic properties of graphene-hexagonal indium telluride superlattices predicts two inequivalent geometrical structures that are almost degenerate in energy. These structures give rise to either gapped states in Kekule phase or gapless states in reconstructed graphene Dirac cones. The results of this study will be useful for exploring the possibility of many-body instabilities in two-dimensional systems.

[Phys. Rev. B 91, 121417(R)] Published Tue Mar 31, 2015

]]>Magnetoelastic coupling describes the interaction between the magnetic degrees of freedom of a material and its strain. This Rapid Communication presents a microscopic model of magnetoelasticity in which all parameters are derived from first-principles calculations. In application to multiferroic materials, the model reveals a new contribution to the electric polarization that appears as a combination of the magnetoelastic and piezoelectric effects. Surprisingly, in the prototypical multiferroic material BiFeO${}_{3}$ the new effect is responsible for a significant share of the total polarization and exceeds the known ionic and electronic contributions.

[Phys. Rev. B 91, 100405(R)] Published Mon Mar 30, 2015

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