It was reported earlier that alkali metal doped picene shows superconductivity at rather high temperatures. In this paper the authors have prepared corresponding material and thoroughly analyzed it using a variety of measurements. They conclude that superconductivity in doped hydrocarbons is questionable casting doubts on previous interpretation of experimental 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 compounds 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

]]>The electron-phonon scattering dominated heat dissipation is difficult to observe in graphene due to the role of impurities in scattering processes. Owing to the suppression of flexural-mode-induced supercollisions in suspended bilayer graphene, the authors of this paper are able to demonstrate that the intrinsic electron-optical phonon coupling governs the heat flow in suspended bilayer graphene samples.

[Phys. Rev. B 91, 121414(R)] Published Fri Mar 27, 2015

]]>Chiral crystals come in left- and right-handed forms. Methods for using electron diffraction to determine crystal chirality have heretofore required the use of multiple scattering and depended sensitively on the sample thickness. Here it is shown that these constraints can be removed with the use of electron vortex beams (which carry orbital angular momentum) in a transmission electron microscope. In accordance with theoretical expectation, the chirality of a sample of Mn${}_{2}$Sb${}_{2}$O${}_{7}$ is experimentally determined.

[Phys. Rev. B 91, 094112] Published Thu Mar 26, 2015

]]>Gd${}_{1-x}$Tb${}_{x}$MnO${}_{3}$ oxides are characterized by two main competing states that exhibit both ferroelectric and multiferroic ordering. Both states involve cycloidal magnetic order that drives ferroelectricity. In their new article, a collaboration of researchers from Japan discovered that exposure of Gd${}_{0.5}$Tb${}_{0.5}$MnO${}_{3}$ to x-ray irradiation induces a reversible transition into a new hidden state, which is also characterized by cycloidal order, but with a different modulation wave vector. The ability to manipulate the state with x-rays suggests a novel route for photocontrol of multiferroic materials.

[Phys. Rev. B 91, 100403(R)] Published Tue Mar 24, 2015

]]>Using infrared excitation at cryogenic temperatures in thin films of GeSbTe compounds, the authors observe persistent-photoconductivity (charge generation by exposure to light without change of stoichiometry) in a material that also exhibits intrinsic electron-glass behavior and has high carrier concentration.

[Phys. Rev. B 91, 094204] Published Mon Mar 23, 2015

]]>Using high-resolution specific heat and SQUID magnetization measurements, this group studies the thermodynamic phase transitions of BaFe${}_{2}$(As${}_{1-x}$P${}_{x}$)${}_{2}$ ($x$=0.0, 0.3). The experiments, assisted by theoretical modeling, show that there is no additional ${2}^{n\phantom{\rule{0}{0ex}}d}$ order “true” nematic phase transition at temperatures above the conventional antiferromagnetic/structural transition.

[Phys. Rev. B 91, 094512] Published Mon Mar 23, 2015

]]>A collaboration of researchers from Japan and France present a comprehensive study of phonon lifetimes and thermal conductivity for 33 zincblende- and wurtzite compounds using linearized phonon Boltzmann equation and first-principles anharmonic phonon calculations. The software that the authors created for this study will be released as an open source package and should be of help in the search of new materials for thermoelectric applications.

[Phys. Rev. B 91, 094306] Published Fri Mar 20, 2015

]]>This European research team reports the first observation of two-photon lasing in a superconducting circuit consisting of a pair of flux qubits strongly coupled to a coplanar waveguide.

[Phys. Rev. B 91, 104516] Published Thu Mar 19, 2015

]]>The emission linewidth is a key figure of merit for a quantum emitter. This paper reports on the possibility of reducing the spectral linewidth of single-wall carbon nanotubes. It demonstrates an order of magnitude narrower linewidths compared to the available data due to the enhanced crystalline quality of the carbon nanotubes synthesized by using a laser ablation technique.

[Phys. Rev. B 91, 121410(R)] Published Wed Mar 18, 2015

]]>For chiral topological phases there exist analytical proofs of a one-to-one correspondence between the low lying spectrum of edge states and that of the entanglement spectrum. Whether or not such an edge-entanglement spectrum correspondence could apply to non-chiral phases has been unclear. Here it is shown that in the Wen-plaquette model, a non-chiral ${Z}_{2}$ topological phase, such a correspondence is exact in the absence of perturbations. While no such correspondence exists in the case of a general perturbation, the correspondence can be shown to apply for perturbations restricted to be translation invariant along the edge/entanglement cut.

[Phys. Rev. B 91, 125119] Published Wed Mar 11, 2015

]]>The electronic band structure of monolayer V${}_{2}$O${}_{5}$ is examined in detail via quasiparticle self-consistent $G\phantom{\rule{0}{0ex}}W$ calculations. There is much interest currently for such layered systems, especially compared to the bulk. Sophisticated calculations like the ones done here can provide key information on the reasons why DFT calculations significantly overestimate or underestimate the band gap in such materials, a perennial issue. The lattice polarization is the major missing ingredient responsible for the discrepancy in this system.

[Phys. Rev. B 91, 125116] Published Tue Mar 10, 2015

]]>The first comprehensive study is made of the exciton dynamics and spin-relaxation processes in isoelectronic centers in GaAs, single excitons bound to two nitrogen atoms. Such atomic defects may offer advantageous properties for quantum information applications over the more established quantum dots and NV centers in diamond. Time-resolved spectroscopy is coupled with a unique analytical model.

[Phys. Rev. B 91, 115201] Published Mon Mar 09, 2015

]]>There is interest in what happens to ultrashort light pulses propagating through a quantum-dot semiconductor optical amplifier waveguide. In this experiment, the influence of nonresonant propagation effects, such as linear dispersion, two-phonon absorption, and Kerr-like, on the intensity and frequency profile of the pulses is shown to be strong enough that they must be included in any modeling.

[Phys. Rev. B 91, 115304] Published Mon Mar 09, 2015

]]>Whether the non-Fermi-liquid behavior of fermionic systems, developing in the proximity of a quantum critical point, is stable or not toward the formation of Cooper pairs is an interesting and challenging open question in the physics of strongly correlated systems. In this new and interesting contribution to the field, the authors study systems where the non-Fermi-liquid behavior arises as a result of the interaction of a gapless bosonic mode with fermions in the vicinity of the Fermi surface.

[Phys. Rev. B 91, 115111] Published Wed Mar 04, 2015

]]>Recent experiments in ultracold atoms and photonic systems have realized lattice models with artificial gauge fields. Here the authors introduce a bosonic version of the Haldane Hubbard Hamiltonian on the honeycomb lattice and use several analytical and numerical methods to uncover a consistent picture of the phase diagram. Three distinct phases are found: chiral superfluid, uniform superfluid, and a plaquette Mott insulator, all of which should be accessible to future experiments.

[Phys. Rev. B 91, 094502] Published Tue Mar 03, 2015

]]>Using a nonequilibrium dynamical mean-field theory the authors study relaxation of a hot-electron distribution coupled to optical phonons. Their main interest is in the adiabatic regime of phonon frequencies smaller than the electronic bandwidth and in an extended analysis of photoemission spectra. In this limit initial coherent phonon oscillations become strongly damped, leaving the system in a mixture of excited polaron states and metastable delocalized states.

[Phys. Rev. B 91, 104301] Published Tue Mar 03, 2015

]]>Nonequilibrium dynamics of interacting quantum many-body physics has recently attracted great attention. The authors address here the nonequilibrium dynamics of a single electron interacting through a Holstein-like coupling with dispersionless phonons on a one dimensional lattice. Using diagonalization in a limited functional space, they identify two different regimes: (1) the relaxation regime where, during a characteristic time scale, a net energy is transferred between the electronic and the phononic subsystem; and (2) the stationary regime, characterized by zero energy transfer and by persisting coherent oscillations in the dynamics of observables.

[Phys. Rev. B 91, 104302] Published Tue Mar 03, 2015

]]>By investigating transport and structural properties of KFe${}_{2}$As${}_{2}$ under pressures up to 33 GPa, this group reveals the presence of two superconducting phases that appear distinct, and each showing strong enhancements in their transition temperature as a function of pressure. The second, higher-${T}_{c}$ phase abruptly appears upon collapse of the tetragonal structure at higher pressures.

[Phys. Rev. B 91, 060508(R)] Published Fri Feb 27, 2015

]]>In this work the authors present a novel mechanism for interfacial superconductivity which has been observed in many materials including high-${T}_{c}$ superconductors. The suggested mechanism is based on an interplay between competing order parameters: superconducting order parameter, and charge- or spin-density wave.

[Phys. Rev. B 91, 064511] Published Fri Feb 27, 2015

]]>This paper presents a comprehensive study of the interplay of Anderson localization and topological phase transitions in five symmetry classes that allow topological insulators in one dimension.

[Phys. Rev. B 91, 085429] Published Fri Feb 27, 2015

]]>There is great interest in understanding the physics of magnetic ordering and electronic transport in materials of reduced dimensionality with strong spin-orbit coupling. This paper presents magnetotransport measurements of Fe${}_{0.28}$TaS${}_{2}$ single crystals, which are found to exhibit very large magnetoresistance (MR) for magnetic fields along the easy axis. The authors believe that such a large MR arises from spin disorder scattering and propose to use this mechanism as a design principle for materials with large MR. Further tests are needed to fully rule out contributions from a more conventional anisotropic MR mechanism.

[Phys. Rev. B 91, 054426] Published Thu Feb 26, 2015

]]>Transparent conducting oxides, such as In${}_{2}$O${}_{3}$, are optically transparent wide band gap semiconductors with high electrical conductivity and are used in applications such as transparent electrical circuits and flat panel displays. Some previous research has argued that conductivity in In${}_{2}$O${}_{3}$ is caused mainly by oxygen vacancies, as in other transparent conducting oxides. Using infrared absorbtion spectroscopy on single-crystal In${}_{2}$O${}_{3}$, the authors show that, consistent with theory, interstital hydrogen forms shallow donors, which make an important contribution to the $n$-type conductivity.

[Phys. Rev. B 91, 075208] Published Tue Feb 24, 2015

]]>Accurate nanoscale atomistic treatment of semiconductor surfaces, together with accurate microscale treatment of electronic effects induced in the semiconductor near-surface region, is crucial for a very large range of issues in modern electronics. However, this has been a difficult challenge for modern computational materials science. In this paper, this goal is achieved by means of a new multiscale approach that couples seamlessly short-range quantum mechanical effects with long-range electrostatic effects. The usefulness of this approach is demonstrated on a variety of silicon surfaces.

[Phys. Rev. B 91, 075311] Published Tue Feb 24, 2015

]]>The authors use photoluminescence- and electrically-detected magnetic resonance spectroscopies to trace and characterize triplet exciton states in lightly fullerene-doped polymers. This approach can provide an improved analysis of charge excitations and their spin dependent interactions in organic electronics devices, in particular organic light emitting diodes, with the potential to enhance their performance.

[Phys. Rev. B 91, 085309] Published Mon Feb 23, 2015

]]>Fractional Quantum Hall (FQH) wave functions are usually obtained in a first-quantized language, using special properties of analyticity of the lowest Landau level (LLL) wave functions. Unfortunately, this formalism is not directly applicable to several systems different from the LLL, such as the recently discovered fractional Chern insulators. Introducing a second-quantized formalism represents an important step towards a new understanding of FQH wave functions in terms of the guiding center degrees of freedom only. In this paper, the authors present several applications of the formalism, including an explicit derivation of the second-quantized version of Read’s string order parameter for the Laughlin state.

[Phys. Rev. B 91, 085115] Published Fri Feb 20, 2015

]]>An important theoretical approach to topologically ordered phases is based on topological field theories. These directly incorporate such important features as the absence of bulk excitations, ground state degeneracy on topologically nontrivial manifolds, and dynamical edge states. The authors construct an effective field theory for a two-dimensional spinless $p$-wave superconductor that describes the topological properties of the bulk state, and also provides a model for the subgap states at vortex cores and edges.

[Phys. Rev. B 91, 075116] Published Thu Feb 19, 2015

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