A microscopic theory for ultrafast spin dynamics across a wide range of energies in magnetic heterostructures has been developed.

[Phys. Rev. B 92, 180412(R)] Published Mon Nov 23, 2015

]]>The physics of underdoped cuprates has been an unresolved longstanding problem. New measurements at ultrahigh magnetic fields on underdoped YBCO are used to show that superconducting diamagnetism survives at fields far above the irreversibility line at low temperatures. Two scenarios can account for these observations - superconductivity competes with charge order and is considerably diminished or a fluctuating superconductivity survives above a certain magnetic field.

[Phys. Rev. B 92, 180509(R)] Published Mon Nov 23, 2015

]]>Through an examination of the dynamic nuclear spin polarization and resonant spin-flip Raman scattering, the authors directly measure the optical-induced Overhauser shift in singly charged (In,Ga)As/GaAs quantum dots. Using a two-color laser excitation scheme, they observe the time evolution of the Overhauser shift, which demonstrates the nuclear spin depolarization over a few seconds. Furthermore, it is shown that this depolarization is strongly dependent on temperature.

[Phys. Rev. B 92, 195421] Published Fri Nov 20, 2015

]]>The perovskite semiconductor CsSnI${}_{3}$ has recently attracted much attention due to its potential applications in solar energy generation. In this work, the authors went beyond the standard (quasi)harmonic approximation, and explained the stability of CsSnI${}_{3}$ at experimental conditions through anharmonic phonon-phonon interactions between the Cs ions and their iodine cages. They also studied the renormalization of the electronic energies due to vibrations and found an unusual opening of the band gap at high temperatures, which demonstrates the importance of anharmonic temperature effects to the realistic modeling of the X(Sn,Pb)Y${}_{3}$ perovskites.

[Phys. Rev. B 92, 201205(R)] Published Fri Nov 20, 2015

]]>There has been some controversy regarding the dominant correlations in weakly doped Hubbard ladders. Analytical approaches find them to be superconducting but numerical approaches have thus far pointed otherwise. Using cutting-edge DMRG techniques on extremely large system sizes this controversy is now resolved to show that superconducting correlations indeed dominate.

[Phys. Rev. B 92, 195139] Published Thu Nov 19, 2015

]]>The two-dimensional superfluid-to-insulator quantum critical point is expected to be accompanied by a collective Goldstone Higgs mode that is massive. However, experimental confirmation within ultracold atoms in an optical lattice is not straightforward. Using Monte Carlo methods and a comparison with recent experiments, the authors of this paper have found that the signature of this massive mode can be observed in the spectral function of the amplitude response under the right conditions.

[Phys. Rev. B 92, 174521] Published Wed Nov 18, 2015

]]>Several established techniques could theoretically be combined to produce a large nuclear polarization in randomly oriented nanodiamonds. This addresses what is currently a critical barrier to the widespread application of nanodiamonds in in-vivo medical diagnostics and MRI.

[Phys. Rev. B 92, 184420] Published Wed Nov 18, 2015

]]>Using angle-resolved photoemission spectroscopy (ARPES), a collaboration of authors from Tokyo and Hiroshima, Japan study the evolution of the nodal d-wave quasiparticles in the trilayer Bi2223 cuprate superconductor across the phase transition into the normal state.

[Phys. Rev. B 92, 195135] Published Wed Nov 18, 2015

]]>The puzzle of the observed nonsaturating and linear magnetoresistance in 3D Dirac materials is addressed by a new mechanism of magnetoresistance in metals that derives from the dynamics of ”squeezed” electrons.

[Phys. Rev. B 92, 180204(R)] Published Mon Nov 16, 2015

]]>Heterostructures of two-dimensional materials have shown unusual properties and rich physical phenomena. This paper reports on micrometer-scale angle-resolved photoemission spectroscopy of van der Waals heterostructures of graphene and MoS${}_{2}$ monolayers. The authors directly measured the electronic structure of monolayer stacking and its tunability due to the twist-angle between the layers. They show that the electronic states of graphene and MoS${}_{2}$ are not hybridized, and the band gap of MoS${}_{2}$ can be engineered by changing the orientation of the two layers.

[Phys. Rev. B 92, 201409(R)] Published Mon Nov 16, 2015

]]>The authors develop an algorithm to identify approximately conserved quantities in models perturbed away from integrability. The authors show that these quantities are able to determine the long time behavior of local correlation functions via Mazur’s inequality. They apply the model to a XXZ Heisenberg perturbed by a next-nearest-neighbor interaction.

[Phys. Rev. B 92, 195121] Published Wed Nov 11, 2015

]]>High-quality $G\phantom{\rule{0}{0ex}}W$ calculations of the quasiparticle band structure in thin films of topological insulator Bi${}_{2}$Se${}_{3}$ show that the topological nature of the surface states is $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t$ the spin-polarized quantum spin Hall state, but the less interesting trivial topology. This is in strong contrast to the expected topology of the surface states of $b\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}k$ Bi${}_{2}$Se${}_{3}$ and the predictions of density functional theory and parametrized calculations for Bi${}_{2}$Se${}_{3}$ thin films, which produce fundamentally less accurate predictions of the band gap than the $G\phantom{\rule{0}{0ex}}W$ approach.

[Phys. Rev. B 92, 201404(R)] Published Mon Nov 09, 2015

]]>The authors explore the possibility of long range coupling between two RX qubits, qubits formed out of sets of triple quantum dots. The coupling is electromagnetic in nature and is facilitated by a superconducting strip line. The authors demonstrate that within this setup, they can implement the quantum iSWAP gate with high fidelity.

[Phys. Rev. B 92, 205412] Published Mon Nov 09, 2015

]]>Martensites, which are the product of diffusionless phase transitions, can form phases with small periodic modulations of crystalline atomic lattice positions. Experiments have shown both that the modulation function is smooth and that when more than one modulation is present they can be incommensurate. These observations have appeared to be inconsistent with nanotwinning models. Here the authors show theoretically that in the case of the ferromagnetic shape memory alloy NiMnGa, the presence of two competing mechanisms favoring different commensurate periodic structures, a result of the interaction between different minima in the energy landscape, can lead to effective smooth incommensurate modulations consistent with nanotwinning models.

[Phys. Rev. B 92, 180101(R)] Published Fri Nov 06, 2015

]]>Cellular dynamical mean-field theory combined with continuous Monte Carlo techniques is used to account for the most important features of the doped quasi-two-dimensional organic Mott insulators.

[Phys. Rev. B 92, 195112] Published Fri Nov 06, 2015

]]>The transport properties of three-dimensional Weyl and Dirac semimetals are studied under a transverse magnetic field. The analysis is based on the continuum Dirac/Weyl model in the presence of potential disorder. The results are successfully compared to recent transport experiments in CdAs.

[Phys. Rev. B 92, 205113] Published Fri Nov 06, 2015

]]>The authors present the first example of a quasi-2D experimental realization of a transverse field Ising model, which is one of the canonical examples of a quantum phase transition driven by quantum mechanical fluctuations induced by a magnetic field applied perpendicular to the preferred direction of the magnetic moments. Experimental realizations of this model are rare, and include the prominently discussed quasi-1D Ising chain system CoNb${}_{2}$O${}_{6}$, and the 3D dipolar-coupled Ising ferromagnet LiHoF${}_{4}$, but the experimental realization of a quasi-2D system has been lacking until now.

[Phys. Rev. B 92, 180404(R)] Published Thu Nov 05, 2015

]]>The modeling of the electronic structure is the key to understanding layered transition-metal dichalcogenides (TMDCs) heterostructures. The authors present a full-range tight-binding hamiltonian for TMDCs by Wannier transformation of density functional theory results, which preserves both the orbital character and phase information. The tight-binding hamiltonians is expected to form the basis for further theoretical investigations of many-body physics and simulations for potential applications under external electric or magnetic fields in finite-size nanostructures, in either monolayer or heterostructure forms.

[Phys. Rev. B 92, 205108] Published Thu Nov 05, 2015

]]>The ability to spectrally resolve phonon energies and dispersion relations is central to the understanding and controlling of structural properties and thermal transport of crystalline solids. However, many of the existing probing techniques are limited by the requirement of large sample sizes. In this work, the authors have demonstrated a new method for determining phonon dispersion relations of solids based upon synchrotron reflection x-ray thermal diffuse scattering measurements. The application of this method was demonstrated in the model system of MgO thin films. Such techniques may become valuable for determining vibrational properties of heteroepitaxial thin films since x-ray penetration depths can be selectively tuned through the use of grazing incidence.

[Phys. Rev. B 92, 174301] Published Tue Nov 03, 2015

]]>It is commonly believed that fractional Chern insulators can only occur in Bloch bands with non-zero Chern numbers. The authors of this paper outline a number of ways in which specifically crafted interactions can be used to create a fractional topological insulator from a noninteracting system with zero Berry curvature.

[Phys. Rev. B 92, 195104] Published Tue Nov 03, 2015

]]>Previous electrical transport experiments on thin films of the topological insulator Bi${}_{2}$Se${}_{3}$ using ferromagnetic contacts have claimed to see spin-momentum locking based on changes in the measured voltage at the contacts. A careful new transport experiment using a unique device configuration reveals that such a voltage arises from fringe magnetic fields. The findings emphasize the necessity of performing detailed experiments so as to exclude effects such as local Hall fields on the measured signal.

[Phys. Rev. B 92, 201102(R)] Published Tue Nov 03, 2015

]]>There are many instances where superconductivity seems to emerge from the condensation of a non-Fermi liquid metal in the vicinity of a quantum critical point. The authors of this paper address this problem by studying a Fermi surface coupled to a critical bosonic order parameter within a large-N approach. The ensuing competition between the tendency for pairing and the destruction of Landau quasiparticles is found to result in a novel non-Fermi liquid fixed point with a finite scale invariant BCS coupling.

[Phys. Rev. B 92, 205104] Published Tue Nov 03, 2015

]]>How does the presence of a finite length scale in a negatively curved spatial geometry, namely the spatial curvature, modify statistical physics properties of many-particle systems such as critical exponents or the texture of ordered states? Here the authors show that phenomena such as unusual magnetization textures and a strong curvature fixed point can emerge, and that this is a promising theoretical approach for investigating uniform frustration and nontrivial critical behavior.

[Phys. Rev. B 92, 134423] Published Fri Oct 30, 2015

]]>Neutron scattering data show that the magnetic response function in the quantum critical region for two different materials, an iron-based superconductor and a heavy fermion compound, compare well to a universal theory.

[Phys. Rev. B 92, 155150] Published Fri Oct 30, 2015

]]>Due to the absence of a strong electron-acoustic phonon interaction, a system made up of graphene sheets encapsulated between thin hexagonal boron nitride slabs is ideal for investigating the hydrodynamic behavior of an electron liquid. Using a fully analytical theoretical approach, the authors demonstrate that nonlocal dc transport measurements can be used to extract the hydrodynamic shear viscosity of 2D electrons in graphene far from the neutrality point. They also suggest that the currently available scanning probe techniques should be able to spatially resolve viscosity-dominated electron flow regions.

[Phys. Rev. B 92, 165433] Published Fri Oct 30, 2015

]]>A thorough test of the eigenstate thermalization hypothesis (ETH) for the single-impurity Anderson model, performed with the aid of the numerical renormalization group (NRG) method, finds good support for ETH. The mechanism responsible for effective thermalization within the NRG can be identified as Anderson orthogonality: the more charge that needs to flow to or from infinity after applying a local excitation within the Wilson chain, the more the system looks thermal afterwards at an increased temperature. For the same reason, however, thermalization fails if charge rearrangement after the excitation remains mostly local. In these cases, the different statistical ensembles lead to different results, and their behavior needs to be understood as a microscopic quantum quench only. This analysis provides new and important insight into the process of thermalization and dynamics of systems exhibiting strong, nontrivial correlations.

[Phys. Rev. B 92, 155435] Published Thu Oct 29, 2015

]]>The authors have investigated the magnetic and structural properties of Fe3PO4O3 using various methods including thermodynamic probes, synchrotron X-ray diffraction, and neutron powder diffraction. In this context, the authors demonstrate the formation of an incommensurate helical antiferromagnetic structure with highly anisotropic domains, which may be produced through magnetoelastic strain that blocks long-range magnetic order. The overall helical nature of the magnetic domains may be of interest to those studying antiferromagnetic Skyrmions and other topological spin textures.

[Phys. Rev. B 92, 134419] Published Mon Oct 26, 2015

]]>Exploiting the analogy between Pfaffian and anti-Pfaffian states the authors construct a particle-hole conjugate of the composite Fermi liquid state. They suggest that a transition between composite Fermi liquid and anti-composite Fermi liquid states may occur at half-filling and discuss the relevance of such transition to recent magnetoresistance oscillation experiments.

[Phys. Rev. B 92, 165125] Published Fri Oct 23, 2015

]]>At low temperatures, the study of iron arsenide superconductors is hindered by the appearance of twin domains that strongly affect superconducting and magnetic properties of the system. To detwin the crystal, a uniaxial pressure is usually applied, which may itself affect the magnetic and electronic properties of the system. In this manuscript, a collaboration of authors from USA, China, France, and Germany develop a technique to obtain de-twinned strain-free samples and use transport measurements and neutron scattering to study electronic nematic phase in electron-doped BaFe${}_{2-x}$Ni${}_{x}$As${}_{2}$. Their results indicate that the in-plane resistivity anisotropy found earlier in uniaxially strained paramagnetic tetragonal phase of iron pnictides is also present in the stress-free samples, but is due to magnetoelastic coupling.

[Phys. Rev. B 92, 134521] Published Thu Oct 22, 2015

]]>The Renyi entropies for an interacting quantum dot are computed under a multi-contour Keldysh formalism. With this in hand, the self-information generating function is determined and the probability distribution of self-information is computed, including the effects of Coulomb interactions in the Hartree approximation. The author argues through these computations that fluctuations in the self-information and the Renyi entropies are tied together intimately and that these fluctuations thus offer a way to give the Renyi entropies physical meaning.

[Phys. Rev. B 92, 165312] Published Thu Oct 22, 2015

]]>The chemical vapor deposition of diamond is known to introduce complexes of silicon, vacancy, and hydrogen. Here the authors theoretically examine several such complexes, some of which have already been observed, others which could potentially form. Using hybrid density functional theory for the treatment of highly correlated orbitals, many measurable quantities are calculated. The SiV${}_{2}$H(-) negatively charged defect is found to be a promising candidate for a long lived solid state quantum memory.

[Phys. Rev. B 92, 165203] Published Tue Oct 20, 2015

]]>This paper reports NMR spin-lattice and spin-spin relaxation rate data for iron arsenide superconductors involving multiple crystals with different dopants, doping levels, and magnetic fields. The results present evidence for glassy nematic fluctuations throughout an extensive region of phase space in these materials. The authors propose that the inhomogeneous relaxation dynamics that dominates the NMR response arises because the dopants introduce quenched random fields which couple to the nematic order. This disorder-induced frustration plays a significant role in suppressing antiferromagnetism and in the emergence of superconductivity.

[Phys. Rev. B 92, 165116] Published Fri Oct 16, 2015

]]>The authors revisited the Mollwo–Ivey relation of $F$ centers in alkali halide crystals, a prototypical color center, based on post-density-functional-theory and post-Hartree-Fock methods. In contrast to earlier interpretations, which stress the importance of the Madelung potential, they find ion-size effects to be the predominant mechanism. These determine the shape of the defect-electron wave function and are responsible for the fractional Mollwo–Ivey exponent of 1.8.

[Phys. Rev. B 92, 144107] Published Wed Oct 14, 2015

]]>The authors apply non-linear spin wave theory to the problem of anisotropic spin-S Heisenberg models on the Kagome lattice. They argue that the non-linear terms of the analysis lead to two unusual effects: 1) the presence of a quantum phase transition as a function of the anisotropy parameter between $q=0$ and $\sqrt{3}\times \sqrt{3}$ order (whereas thermal fluctuations favor the $\sqrt{3}\times \sqrt{3}$ order regardless of the strength of the anisotropy) and 2) strong quantum effects in the spectral features that are not suppressed with $1/S$ as is typical.

[Phys. Rev. B 92, 144415] Published Tue Oct 13, 2015

]]>Magnetic force measurements are used to measure the penetration depth and pinning forces for vortices in the superconductor NdFeAsO${}_{1-x}$F${}_{x}$.

[Phys. Rev. B 92, 134509] Published Mon Oct 12, 2015

]]>The use of terahertz time-resolved studies in conducting and superconducting systems is gaining considerable interest, especially in the light of recent studies demonstrating induction of superconductivity in various materials with optical impulsive excitation. The authors carry out a theoretical analysis of the response functions typically measured by terahertz time-domain spectroscopy (THz-TDS) in metallic and superconducting samples. Within the Drude model, the authors found that THz-TDS does not simply measure the instantaneous conductivity change, in agreement with previous reports. They identify limits wherein the time-resolved THz-TDS spectrum does and does not approach the instantaneous conductivity change. They further show that the difference between the THz-TDS response and the instantaneous conductivity is largest when the photo-induced state changes from a normal metal to a superconductor.

[Phys. Rev. B 92, 134507] Published Fri Oct 09, 2015

]]>A fundamental question for understanding the decoherence of quantum spin qubits interacting with a bath of spins in the environment is the nature of the noise affecting the qubit - can it be modeled as classical noise or are quantum effects important? Here the authors experimentally demonstrate that in the favorable case of bismuth electron spin donors in silicon near values of a magnetic field known as clock transitions, the nuclear spin noise can be approximated as classical Gaussian noise. This finding is expected to influence efforts to optimize the control of qubits in silicon based quantum computation.

[Phys. Rev. B 92, 161403(R)] Published Thu Oct 08, 2015

]]>Previous studies have shown that the nuclear spin polarization in GaAs is spatially inhomogeneous. The authors of this paper argue that the hyperfine interaction between the electron spins and inhomogeneous nuclear field is of Dyakonov-Perel type. They show that the inclusion of corresponding anisotropic spin relaxation mechanism produces a better fit of the experimentally measured Hanle effect.

[Phys. Rev. B 92, 140201(R)] Published Wed Oct 07, 2015

]]>Anomalies in transport and thermodynamic quantities near a quantum critical point in the heavy fermion compound YbRh${}_{2}$Si${}_{2}$ are shown to be caused by the onset of spin-flip scattering above a certain crossover line in the T-H phase diagram.

[Phys. Rev. B 92, 155111] Published Wed Oct 07, 2015

]]>WTe${}_{2}$ has recently been reported to exhibit extremely large magnetoresistance, which may find potential applications in devices such as highly sensitive magnetic sensors and hard drives. In this paper, using ultrafast optical spectroscopy, the authors track the relaxation of photoexcited carriers in the time domain as they return to equilibrium in WTe${}_{2}$. Their experimental results not only resolve the time scales that ultimately limit potential applications of this material in electronic devices, e.g., high-speed hard drives, but also shed new light on the mechanisms governing the extremely large magnetoresistance.

[Phys. Rev. B 92, 161104(R)] Published Wed Oct 07, 2015

]]>The authors investigate the magnetothermoelectrical properties of an individual magnetic domain wall in a permalloy nanowire. They show that the thermopower contribution of a domain wall in a magnetic nanowire provides a underlying coupling of the magnetic structure and overall thermoelectric fingerprint. The observation of a domain wall magneto-Seebeck effect is further explained through a magnetization-dependent Seebeck coefficient of permalloy in combination with the local spin configuration of the domain wall.

[Phys. Rev. B 92, 140405(R)] Published Tue Oct 06, 2015

]]>The authors investigate the application of an “impurity” or inhomogeneous dynamical mean-field theory (DMFT) to two magnetic impurities on the surface of a 3D cubic lattice and coupled quantum dots. This work also compares the combination of a local self-energy with self consistency, which produces dramatically nontrivial results, with the exact solutions provided by the numerical renormalization group (NRG). Furthermore, the authors provide the limits where the local self-energy fails.

[Phys. Rev. B 92, 155101] Published Thu Oct 01, 2015

]]>The authors present evidence of many-body localization in a translationally invariant model Hamiltonian. The model, Ising-like, arises in the study of quantum glasses. The authors show that this model exhibits two regimes: one of fast relaxation and one of slow relaxation with dynamical features typically associated with many-body localized phases.

[Phys. Rev. B 92, 100305(R)] Published Mon Sep 28, 2015

]]>Motivated by a deeper understanding of strongly interacting topological phases and fractional Chern insulators the authors propose a formulation of a discretized Chern-Simon theory on random lattices and graphs.

[Phys. Rev. B 92, 115148] Published Mon Sep 28, 2015

]]>The authors demonstrate a means to determine the strength of excitonic correlations (as measured by the photoluminescence energy shift) of indirect excitons in semiconductor quantum wells. Because this energy shift is determined by how the excitons respond to an external potential, the authors apply an electrostatic periodic potential to the excitonic gas. By measuring the corresponding excitonic response due to this applied potential, they, using a complementary theory, are able to deduce the strength of correlations.

[Phys. Rev. B 92, 115311] Published Mon Sep 28, 2015

]]>It is generally expected that Majorana qubits are immune to decoherence at the hardware level for topological reasons. The authors investigate this question in detail and show that this is not true in a specific, widely studied, quantum computing architecture.

[Phys. Rev. B 92, 115441] Published Fri Sep 25, 2015

]]>This paper reports on successful application of electron energy loss spectroscopy (EELS) for probing low-energy electronic excitations at all values of momentum transfer with atomic-scale spatial resolution. In this regard EELS appears to be complementary to optical spectroscopy which probes only direct excitations with limited spatial resolution. The authors suggest that EELS can be used to study atomic-scale structural, electronic, magnetic and vibrational properties of systems having defects and impurities as well.

[Phys. Rev. B 92, 125147] Published Fri Sep 25, 2015

]]>The authors present an experimental mechanism for converting the state of a spin qubit in a quantum dot device into different charge states. This mechanism depends on metastable charge states present when the device has very asymmetric couplings to the external leads. This approach is used to observe Landau-Zener-Stuckelberg oscillations of the (S-${T}_{+}$) qubit.

[Phys. Rev. B 92, 125434] Published Fri Sep 25, 2015

]]>The non-equilibrium Anderson impurity model is solved to an unprecedented accuracy to obtain its spectral properties in the steady state using a recently developed approach.

[Phys. Rev. B 92, 125145] Published Thu Sep 24, 2015

]]>The authors theoretically study optical transitions in transition-metal dichalcogenides. In particular, they explain the difference between the excitonic properties of monolayer MoSe${}_{2}$ and WSe${}_{2}$. Excitons in WSe${}_{2}$ are thought to be bound to impurities. An alternative theory presented in this paper suggests that these excitons correspond to low-energy optical transitions. The authors also put forward an alternative explanation as to why the excitons in MoSe${}_{2}$ have vanishing polarization. They attribute this phenomenon to polaron-induced Rabi oscillations between dark and bright excitons.

[Phys. Rev. B 92, 125431] Published Wed Sep 23, 2015

]]>When a wave is incident on an open random medium it is decomposed into a number of “partial waves” that propagate independently along natural channels, the so-called transmission eigenchannels, and are superposed again when they leave the medium. Here, the authors propose the use of asymmetric edge reflection (the asymmetry in the reflections of the sample edges) to control the perfectly transmitting eigenchannel in a quasi-one-dimensional diffusive medium.

[Phys. Rev. B 92, 094203] Published Mon Sep 21, 2015

]]>The fractional quantum Hall effect is traditionally viewed as a distinctive attribute of strongly-interacting electron systems. This paper develops an alternative picture which suggests that the low energy quantum states corresponding to an experimentally observable filling fractions can be identified by simply having an exceptionally high degeneracy in the noninteracting limit.

[Phys. Rev. B 92, 125427] Published Mon Sep 21, 2015

]]>Using a variational ansatz based on matrix product states, the authors present a methodology for determine the elementary excitations and their low energy scattering matrices of general quasi-one-dimensional spin systems. From these scattering matrices, the authors map the system unto an effective integrable model and then employ the thermodynamic Bethe ansatz so as to determine thermodynamic properties of the spin system. As a demonstration of the method, the authors apply it to a Heisenberg spin ladder.

[Phys. Rev. B 92, 125136] Published Fri Sep 18, 2015

]]>Quantum spin liquids are elusive states of matter, which have been predicted more than four decades ago but have not so far been conclusively sighted in nature. In this paper the authors study the so called ‘extended Kitaev model’, which has a number of different quantum spin-liquid phases including one with non-Abelian excitations. They present a solution of a long standing problem for this model, namely, the problem of obtaining the dynamical response function. Using a rarely available exact calculation, they find that there are indeed clear signatures in the spin structure factor betraying the presence of spin-liquids and their fractionalized quasi-particles, including those with non-Abelian statistics.

[Phys. Rev. B 92, 115127] Published Mon Sep 14, 2015

]]>Entanglement in quantum many-body systems is one of the most challenging and fascinating recent trends in the study of complex quantum systems. A physical interpretation of the concept of “entanglement contour” is given using quantum many-body constructs and is generalized to the case of both fermionic and bosonic Hamiltonians within a unified framework. The relationship to number fluctuations and entropy is explored in a variety of free (quadratic) many-body systems.

[Phys. Rev. B 92, 115129] Published Mon Sep 14, 2015

]]>The coupling of the electric and magnetic degrees of freedom in condensed matter systems has long been an area of basic and applied research. In a 2013 PRL (PRL 110, 137205), a coupling energy term between the electromagnetic angular momentum density and the magnetization of a material was proposed. In this PRB, the authors provide a direct link between the proposed coupling term and the Dirac equation. They demonstrate that the Dirac equation leads to an interaction Hamiltonian (which they refer to as “angular magnetoelectric”, or AME, coupling Hamiltonian) that couples linearly the electron spin and the electromagnetic field’s angular momentum. They show that the AME coupling Hamiltonian has an expectation value that for some materials (e.g., ferromagnets) is equal to the recently proposed energy coupling, and that it contributes to the Inverse Faraday Effect. The AME coupling Hamiltonian may lead to the prediction and understanding of novel magnetoelectric and magneto-optical phenomena.

[Phys. Rev. B 92, 100402(R)] Published Fri Sep 11, 2015

]]>The spin susceptibility in strontium ruthenate is shown to undergo an increase when the material goes superconducting, a result in variance with most superconductors that we know. This behavior, once predicted for ${}^{3}$He too, is the surest sign that strontium ruthenate is a spin-triplet superconductor.

[Phys. Rev. B 92, 100502(R)] Published Fri Sep 11, 2015

]]>Two-dimensional Fourier transform (2DFT) spectroscopy is a cutting-edge technique to investigate nonlinear many-body physics in semiconductor nanostructures. This paper reports an experimental and theoretical study of 2DFT on a high-quality GaAs-based semiconductor microcavity to gain an understanding of polariton self-interactions and polariton cross-interactions and their effects on the 2D spectra.

[Phys. Rev. B 92, 125415] Published Fri Sep 11, 2015

]]>Ultrafast magnetization switching in ferrimagnets by an external laser pulse have been an active area of research in the last several years. Experimentally, the most intensively studied materials in which this phenomenon occurs are ferrimagnetic amorphous alloys, while the theoretical effort has been mostly concentrated on periodic crystalline structures. Understanding how and to what extent the inhomogeneity of the materials affects the magnetization switching is the focal point of this manuscript. By combining the first principles calculations with an atomistic model of the magnetization dynamics the authors construct a multi-scale theory that reproduces the experimentally observed magnetization dynamics in Gd-Fe alloys.

[Phys. Rev. B 92, 094411] Published Wed Sep 09, 2015

]]>This theoretical study provides an exact implementation of the CNOT two-qubit gate operation between capacitively coupled exchange-only qubits defined by three electrons in triple quantum dots. The authors show that the CNOT gate can be implemented by tuning three parameters: the two single-qubit exchange splittings, and the duration of the pulse.

[Phys. Rev. B 92, 125409] Published Wed Sep 09, 2015

]]>GaAs is the prototype material considered as a replacement for silicon in CMOS technology owing to its high electron mobility. However, the high density of interfacial defect states found at GaAs/oxide interfaces, which prevents the proper operation of GaAs-based devices through Fermi-level pinning, hinders the development of GaAs-based technology. In this thorough first-principles study of defects at the GaAs/Al${}_{2}$O${}_{3}$ interface, the authors deliver results that are very significant for the identification of the origins of Fermi-level pinning at these interfaces.

[Phys. Rev. B 92, 125304] Published Tue Sep 08, 2015

]]>Shear viscosity for a fermionic fluid described by a single band Hubbard model is computed using dynamical mean field theory and found to violate the quantum limit.

[Phys. Rev. B 92, 125103] Published Tue Sep 01, 2015

]]>A new computational method is introduced that allows interpolation of the electron-phonon matrix elements in the space of localized Wannier functions, extending a previous method for study of polar semiconductors. The amount of broadening of the bands in GaAs due to electron-phonon scattering is presented, showing good agreement with experimental results. The method is shown to perform better than an empirical pseudopotential.

[Phys. Rev. B 92, 054307] Published Mon Aug 31, 2015

]]>The authors study the competing ferromagnetic (FM) and antiferromagnetic (AFM) interactions in the quantum spin ice candidate Yb${}_{2}$Ti${}_{2}$O${}_{7}$ using various probes and techniques. They show that it produces a continuum of broad excitations, where the coexistence of different magnetic characteristics indicates the compound lies at the FM and AFM phase boundary for the material. This suggests that the competition of states produces an unconventional ground state through quantum fluctuations.

[Phys. Rev. B 92, 064425] Published Mon Aug 31, 2015

]]>A systematic study of both the harmonic response and spin torque ferromagnetic resonance demonstrates that the spin Hall torque efficiency in a Pt-ferromagnetic (FM) structure is strongly dependent on the interface properties and the choice of the ferromagnetic materials, a key point that has until now not been made in spin Hall studies.

[Phys. Rev. B 92, 064426] Published Mon Aug 31, 2015

]]>In${}_{2}$O${}_{3}$ and Ga${}_{2}$O${}_{3}$ are both transparent conducting oxides with advantageous properties, but differing crystal structures. Alloying the two together could permit the tuning of materials properties such as band gaps, but raises the question of what the stable crystal structure would be. Using state of the art first principles calculations, the authors predict alloy properties as a function of composition, finding the structure with the lowest formation barrier. They also report natural band alignments which can aid in the design of heterostructures.

[Phys. Rev. B 92, 085206] Published Mon Aug 31, 2015

]]>The authors study classical Heisenberg antiferromagnets with long-range interactions in two and three dimensions. These antiferromagnets can arise as effective models of diluted Coulomb spin liquids in the zero-temperature limit. The authors develop a phase diagram of these models as a function of the strength of the effective interaction strength.

[Phys. Rev. B 92, 085144] Published Tue Aug 25, 2015

]]>The authors study the stuffed metallic pyrochlore Pr${}_{2+x}$Ir${}_{2-x}$O${}_{7-\delta}$ through specific heat, elastic neutron scattering, and muon spin rotation ($\mu $SR) measurements. They consider the question of why the static local field (B${}_{l\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}c}$) as measured in $\mu $SR is so small. They weigh two possible theories, the fluctuating-moment picture and the suppressed-moment picture, and argue that the available evidence leans toward the former, while stating that regardless of picture, this pyrochlore is very close to a magnetic-nonmagnetic critical point.

[Phys. Rev. B 92, 054432] Published Mon Aug 24, 2015

]]>Using a novel hydrothermal ion-exchange technique, large and high-quality optimally doped single crystals of the new superconductor (Li${}_{0.84}$Fe${}_{0.16}$)OHFe${}_{0.98}$Se have been successfully synthesized for the first time. Thanks to these single-crystal samples, the anomalous normal-state properties of a linear in-plane electric resistivity, a dip in the Hall coefficient, and a linear magnetic susceptibility are revealed for the first time.

[Phys. Rev. B 92, 064515] Published Mon Aug 24, 2015

]]>Using bcc Fe as a playground, the authors investigate the presence of chiral degeneracies in realistic band structures of ferromagnetic materials. They find ubiquitous Weyl points and demonstrate that Chern numbers can be transferred between Fermi sheets by varying the Fermi level or an external parameter such as the magnetization direction.

[Phys. Rev. B 92, 085138] Published Fri Aug 21, 2015

]]>Heavy fermion systems are useful for studying quantum criticality because the low energy scale associated with their large effective mass can be tuned by nonthermal control parameters. Here, Shubnikov-de Haas oscillations are observed in YbPtBi, a heavy fermion compound with an exceptionally large effective mass for electrons, at a high magnetic field that reveals the shape of the Fermi surface. In the future these observations, when combined with additional data at lower magnetic fields, could provide important information about quantum criticality in these systems.

[Phys. Rev. B 92, 085135] Published Thu Aug 20, 2015

]]>To understand the pairing symmetry and superconducting transition temperature in heavily electron-doped iron-based superconductors, it is important to study more of these materials, especially ones with decent stability in air and without phase separation. Here, angle-resolved photoemission spectroscopy probes the surface electronic structure and superconducting gap in the new superconductor (Li${}_{0.8}$Fe${}_{0.2}$)OHFeSe, which shows a ${T}_{c}$ as high as 40 K.

[Phys. Rev. B 92, 060504(R)] Published Tue Aug 18, 2015

]]>Longitudinal magnetoresistance has recently been used as an experimental tool to identify exotic topological phases such as Weyl semimetals. The authors of this paper show that in the presence of certain scattering mechanisms generic materials can demonstrate similar characteristics as well, including negative longitudinal magnetoresistance.

[Phys. Rev. B 92, 075205] Published Mon Aug 17, 2015

]]>Muonium is like hydrogen, but with a positively charged muon instead of a proton at the center. Observing muon spin rotation in a single crystal of TiO${}_{2}$, and comparing to existing data for hydrogen, the authors demonstrate that the defect configuration and electronic structure are the same for both. This provides important support for research which uses muons as a substitute for hydrogen in semiconductors.

[Phys. Rev. B 92, 081202(R)] Published Mon Aug 17, 2015

]]>The authors in this work consider the orthogonality catastrophe in a new context, that of disordered quantum spin chains. Here the orthogonality catastrophe arises from measuring the overlap of the spin chain’s ground state before and after cutting the system into two. Unlike the orthogonality catastrophe in a metal, here the orthogonality catastrophe exhibits multifractality: different disorder-averaged moments of the overlap exhibit different scaling exponents with system size.

[Phys. Rev. B 92, 054203] Published Fri Aug 14, 2015

]]>The connection between the spin-orbit torque (SOT) and inverse spin-orbit torque (ISOT) in systems without inversion symmetry is studied by combining phenomenological models, diffusion theory, and density functional theory. Using this, DFT calculations on Co/Pt(111) magnetic bilayers expose the mechanisms underlying SOT and ISOT and highlight their reciprocity on the microscopic level.

[Phys. Rev. B 92, 064415] Published Wed Aug 12, 2015

]]>At low temperatures, the longitudinal resistivity of metallic systems exhibits quantum oscillations when submitted to a sufficiently high magnetic field. The authors report magneto-transport study of a high quality magnetic two-dimensional electron gas formed in a diluted magnetic CdMnTe quantum well. They find that the Shubnikov-de Haas characteristics is well-described by incorporating the electron Mn exchange interaction into the traditional Lifshitz-Kosevich formalism in a “mean field” approach.

[Phys. Rev. B 92, 085304] Published Wed Aug 12, 2015

]]>Motivated by the possibility of experimental detection of the topological magnetoelectric effect the authors put forth a theoretical proposal for its realization in the zero plateau quantum anomalous Hall state of a ferromagnet-topological insulator heterostructure.

[Phys. Rev. B 92, 081107(R)] Published Mon Aug 10, 2015

]]>Organic molecular magnets like piperazinium hexachlorodicuprate (PHCC) have attracted interest due to their sensitivity to pressure which presents possibilities for pressure-induced quantum phase transitions. Previous neutron and muon studies of PHCC gave differing indications of how the spin gap in this material varied with applied pressure. The authors of this work have resolved this discrepancy by further neutron scattering results showing that the spin gap has dissipated completely by 9 kbar, in agreement with the previous muon data. The authors also present a model in which the results are explained by the weakening of a single exchange pathway.

[Phys. Rev. B 92, 054413] Published Fri Aug 07, 2015

]]>The authors describe two theoretical setups that could be used to demonstrate the yet unobserved topological magnetoelectric effect. The first proposal employs the zero-filling quantum Hall effect in thin films under magnetic field. The second setup involves topological insulator thin films doped with two magnetic ions such as Cr and Mn.

[Phys. Rev. B 92, 085113] Published Fri Aug 07, 2015

]]>For several decades LaCoO${}_{3}$ attracted interest due the unconventional thermally-driven spin-state crossover from a nonmagnetic to paramagnetic state. More recently, it was realized that the “nonmagnetic” ground state harbors some form of magnetism that is likely due to local magnetic entities forming at oxygen vacancies. Such entities dubbed “magnetic excitons” were predicted in 1996, with some evidence for their existence emerging around 2005 from muon spin relaxation. In this Rapid Communication the authors provide the first scattering-based evidence for spin excitons, direct information on the size and density of the excitons, as well as their interactions. The form of the scattering is also direct proof of a bulk 3D ensemble of these excitons.

[Phys. Rev. B 92, 060404(R)] Published Thu Aug 06, 2015

]]>The shift of attention in topological matter is quickly shifting from topological insulators to Weyl semimetals after the recent much publicized theoretical prediction and experimental verification in TaAs. Reported here is the first Raman study of a Weyl semimetal. As with topological insulators, Raman phonons will be routinely used as probes to characterize the quality and the conditions of samples and devices. The study here identifies all the optic phonon modes and finds some additional interesting features, and should provide a good guide for future work.

[Phys. Rev. B 92, 064302] Published Thu Aug 06, 2015

]]>The authors study the diluted spin-half Heisenberg model near the percolation threshold using Schwinger boson mean field theory (SBMFT). They show how SBMFT predicts the emergence of effective local spin degrees of freedom. They demonstrate that SBMFT applied to dilute spin systems is qualitatively accurate by also performing DMRG computations.

[Phys. Rev. B 92, 064401] Published Mon Aug 03, 2015

]]>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

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