Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strai…

[Phys. Rev. B 94, 214104] Published Thu Dec 08, 2016

]]>We propose a scheme which can generate a highly directional single photon with almost 100% efficiency. Therefore we can get a useful single photon when it is required. An initial excited atom is placed inside a special Fabry-Pérot cavity whose walls consist of left-handed and zero-index metamaterial…

[Phys. Rev. B 94, 220103(R)] Published Thu Dec 08, 2016

]]>We present diffuse x-ray scattering data on the strong negative thermal expansion (NTE) material ${\mathrm{ScF}}_{3}$ and find that two-dimensional nanoscale correlations exist at momentum-space regions associated with possibly rigid rotations of the perovskite octahedra. We address the extent to which rigid octahe…

[Phys. Rev. B 94, 214102] Published Wed Dec 07, 2016

]]>We report a Raman scattering study of six rare-earth orthoferrites $R{\mathrm{FeO}}_{3}$, with $R$ = La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of ${\mathrm{SmFeO}}_{3}$ and first-principles calculations enable the assignment of the observed phonon modes to vibrational symmetries and atomic displacements…

[Phys. Rev. B 94, 214103] Published Wed Dec 07, 2016

]]>Recent experiments on ice formed by water under nanoconfinement provide evidence for a two-dimensional (2D) “square ice” phase. However, the interpretation of the experiments has been questioned and the stability of square ice has become a matter of debate. Partially this is because the simulation a…

[Phys. Rev. B 94, 220102(R)] Published Tue Dec 06, 2016

]]>Single crystals of ${\mathrm{PbZrO}}_{3}$ have been studied by dynamic mechanical analysis measurements in the low-frequency range $f=0.02$–50 Hz. The complex Young's modulus exhibits a quite rich behavior and depends strongly on the direction of the applied dynamic force. In pseudocubic ${\left[100\right]}_{c}$ direction, we found in…

[Phys. Rev. B 94, 214101] Published Fri Dec 02, 2016

]]>Phase decomposition is a well-known process leading to the formation of two-phase mixtures. Here we show that a strain imposed on a ferroelastic crystal promotes the formation of mixed phases and domains, i.e., strain phase separation with local strains determined by a common tangent construction on…

[Phys. Rev. B 94, 220101(R)] Published Fri Dec 02, 2016

]]>In the conceptual framework of phase ordering after temperature quenches below transition, we consider the underdamped Bales-Gooding-type “momentum conserving” dynamics of a 2D martensitic structural transition from a square-to-rectangle unit cell. The one-component or ${N}_{\mathrm{OP}}=1$ order parameter is one o…

[Phys. Rev. B 94, 224101] Published Fri Dec 02, 2016

]]>Extensive *ab initio* simulations of ice-water basal interface at seven temperatures in the range 250–400 K were performed in NVT and NPT ensembles with a collection of 389 water molecules in order to estimate the melting point of ice from direct liquid-solid two-phase coexistence. Density functional …

[Phys. Rev. B 94, 184111] Published Tue Nov 29, 2016

]]>We present a comprehensive density-functional theory study of total energy and structural properties of As, Sb, and Bi in their A7 ground-state structure and in the bcc, fcc, and simple cubic (sc) modifications. We also investigate continuous structural transitions between these structures. The elec…

[Phys. Rev. B 94, 184110] Published Mon Nov 28, 2016

]]>Structural stability, electronic structure, and optical properties of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{BaI}}_{3}$ hybrid perovskite are examined from theory as well as experiment. Solution-processed thin films of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{BaI}}_{3}$ exhibited a high transparency in the wavelength range of 400–825 nm (1.5–3.1 eV for which the photon current …

[Phys. Rev. B 94, 180105(R)] Published Wed Nov 23, 2016

]]>The formalism to construct the machine learning potentials (MLPs) is presented. We introduce the spilling factor for the simultaneous error estimation and the recursive bisection method for the reduction of the computational cost. The formalism is applied for the $\beta $-phase vanadium monohydride. The fi…

[Phys. Rev. B 94, 184109] Published Wed Nov 23, 2016

]]>Ferroelectric materials encode information through the displacement of atoms within the unit cell, but the ultimate speed limits governing how fast the polarization can change and how it responds to electric fields remain largely unknown. These processes in turn fundamentally determine the functionality of ferroelectric materials within devices. Here, the authors show that single-cycle light pulses at terahertz frequencies can be used as an ultrafast electric field to drive large amplitude rotations of the ferroelectric polarization on picosecond time scales within the prototypical ferroelectric BaTiO${}_{3}$, probed by femtosecond x-ray scattering to directly resolve the motions of the atoms. These measurements are connected directly to first-principles molecular dynamics simulations of ultrafast electric-field-driven effects in ferroelectrics with good agreement obtained between experiment and theory.

[Phys. Rev. B 94, 180104(R)] Published Tue Nov 22, 2016

]]>Using the Landau-Ginzburg-Devonshire theory, we established the role of the flexoelectric coupling between the gradients of elastic strain and polarization in the stability of spatially modulated phases in ferroics, such as incipient and proper ferroelectrics with commensurate and incommensurate lon…

[Phys. Rev. B 94, 174112] Published Mon Nov 21, 2016

]]>Both ${180}^{\circ}$ and ${90}^{\circ}$ intrinsic polarization switching (IPS) in $\mathrm{BaTi}{\mathrm{O}}_{3}$ crystal were investigated by Landau-Ginzburg-Devonshire (LGD) theory under combined electric field and stress loading. Results show that for ${180}^{\circ}\phantom{\rule{0.16em}{0ex}}\mathrm{PS}$, the coercive electric field $\left({E}_{IC}^{{180}^{\circ}}\right)$ increases under tension but decreases under co…

[Phys. Rev. B 94, 184108] Published Mon Nov 21, 2016

]]>First-principles methods are employed to determine the structural, mechanical, and thermodynamic reasons for the experimentally reported cubic WN phase. The defect-free rocksalt phase is both mechanically and thermodynamically unstable, with a negative single crystal shear modulus ${C}_{44}=\phantom{\rule{0.16em}{0ex}}-86\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and a p…

[Phys. Rev. B 94, 174111] Published Fri Nov 18, 2016

]]>Motivated by the resurgence of electronic and optical property design in ordered fluoride and oxyfluoride compounds, we present a density functional theory (DFT) study of 19 materials with structures, ranging from simple to complex, and variable oxygen-to-fluorine ratios. We focus on understanding t…

[Phys. Rev. B 94, 174108] Published Wed Nov 16, 2016

]]>The $\mathrm{Xe}\text{\u2212}{\mathrm{N}}_{2}$ binary phase diagram was determined at 296 K from the pressure evolution of 14 different concentrations. The properties of $\mathrm{Xe}\text{\u2212}{\mathrm{N}}_{2}$ mixtures were characterized using visual observation, Raman spectroscopy, and powder x-ray diffraction. Above 4.9 GPa, the $\mathrm{Xe}({\mathrm{N}}_{2}{)}_{2}$ van der Waals compound is stab…

[Phys. Rev. B 94, 174109] Published Wed Nov 16, 2016

]]>We study the temperature dependence of the charge density wave (CDW) in a chromium thin film using x-ray diffraction. We exploit the interference between the CDW satellite peaks and Laue oscillations to determine the amplitude, the phase, and the period of the CDW. We find discrete half-integer peri…

[Phys. Rev. B 94, 174110] Published Wed Nov 16, 2016

]]>A equation of state (EOS) experimental technique that enables the study of thermodynamic derivatives into the TPa regime is described and applied to boron carbide (${\mathrm{B}}_{4}\mathrm{C}$). Data presented here are principal Hugoniot sound speed measurements reported using a laser-driven shock platform, providing a mean…

[Phys. Rev. B 94, 184107] Published Wed Nov 16, 2016

]]>We report a study of the strain state of epitaxial MnSi films on Si(111) substrates in the thick film limit (100–500 Å) as a function of film thickness using polarization-dependent extended x-ray absorption fine structure (EXAFS). All films investigated are phase-pure and of high quality with a shar…

[Phys. Rev. B 94, 174107] Published Tue Nov 15, 2016

]]>We have conducted high-pressure x-ray diffraction and Raman spectroscopic studies on the $\mathrm{CdC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{e}}_{4}$ spinel at room temperature up to 42 GPa. We have resolved three structural transitions up to 42 GPa, i.e., the starting $Fd\overline{3}m$ phase transforms at $\sim 11\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ into a tetragonal $I{4}_{1}/amd$ structure, an orthorhom…

[Phys. Rev. B 94, 174106] Published Mon Nov 14, 2016

]]>We report on transmission electron microscope beam-induced ferroelectric domain nucleation and motion. While previous observations of this phenomenon have been reported, a consistent theory explaining induced domain response is lacking, and little control over domain behavior has been demonstrated. …

[Phys. Rev. B 94, 174104] Published Fri Nov 11, 2016

]]>We analyze theoretically the finite-temperature polarization dynamic in displacive-type ferroelectrics. In particular we consider the thermally activated switching time of a single-domain ferroelectric polarization studied by means of the Landau-Khalatnikov equation, extended to capture thermal fluc…

[Phys. Rev. B 94, 174105] Published Fri Nov 11, 2016

]]>This paper reports on symmetry breaking in the aperiodic inclusion compound $n\text{-octadecane/urea}$ and its isotopomer $n\text{-octadecane/urea-}{d}_{4}$. The high-symmetry phase is described by a hexagonal rank-4 superspace group. Pretransitional phenomena in this crystallographic superspace reveal competing short-ran…

[Phys. Rev. B 94, 184105] Published Fri Nov 11, 2016

]]>We investigated the crystal structures and dielectric properties of an improper ferroelectric ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_{x}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}(x\le 0.1)$ and revealed that suppressing the condensation of the $M$-point soft mode involves the emergence of a “fluctuating” state. In the low-Sr-concentration region of $x\le 0.06$, crystals exhibit …

[Phys. Rev. B 94, 184106] Published Fri Nov 11, 2016

]]>We have examined the effects of field cooling on the phase diagram of the relaxor system $(1-x)\mathrm{Pb}\left(\mathrm{Z}{\mathrm{n}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}\right){\mathrm{O}}_{3}-x\mathrm{PbTi}{\mathrm{O}}_{3}$ (PZN-$x\mathrm{PT}$) for compositions near the morphotropic phase boundary (MPB). High-resolution diffraction measurements using Cu ${K}_{\alpha}$ x rays, which probe $\approx 3\phantom{\rule{0.16em}{0ex}}\mu \mathrm{m}$ below the crystal surface, were …

[Phys. Rev. B 94, 174103] Published Thu Nov 10, 2016

]]>Magnetic skyrmions are candidates for a new generation of information carriers due to their nanometric size and topologically protected stability. The study of the dynamics of such skyrmions in racetrack geometries and, in general, in confined geometries becomes essential to achieve these goals. Her…

[Phys. Rev. B 94, 184104] Published Thu Nov 10, 2016

]]>Entropy is a critical, but often overlooked, factor in determining the relative stabilities of crystal phases. The importance of entropy is most pronounced in softer materials, where small changes in free energy can drive phase transitions, which has recently been demonstrated in the case of organic…

[Phys. Rev. B 94, 180103(R)] Published Mon Nov 07, 2016

]]>Ferroelectric polymorphic phase coexistence, associated with either the presence of a morphotropic phase boundary or a temperature-driven polymorphic phase transition, is currently acknowledged as the key to high piezoelectric activity and is searched when new perovskite materials are developed, lik…

[Phys. Rev. B 94, 184101] Published Mon Nov 07, 2016

]]>Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heusler…

[Phys. Rev. B 94, 184102] Published Mon Nov 07, 2016

]]>We consider a film of a normal-state Fermi liquid on a planar substrate. Landau's Fermi liquid theory is applied to calculate the linear response of the film to transverse oscillation of the substrate. The response consists of a collective transverse zero-sound mode, as well as incoherent quasiparti…

[Phys. Rev. B 94, 184103] Published Mon Nov 07, 2016

]]>The effect of atomic *short-range* order on the macroscopic and microscopic properties of the prototype of relaxor ferroelectrics, that is, lead magnesium niobate $\mathrm{Pb}\left({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}\right){\mathrm{O}}_{3}$ (PMN), is studied via the combination of an annealing technique and a large-scale effective Hamiltonian method. The invest…

[Phys. Rev. B 94, 180102(R)] Published Thu Nov 03, 2016

]]>We explore the role of flexoelectric effect in functional properties of nanoscale ferroelectric films with mixed electronic-ionic conductivity. Using a coupled Ginzburg-Landau model, we calculate spontaneous polarization, effective piezoresponse, elastic strain and compliance, carrier concentration,…

[Phys. Rev. B 94, 174101] Published Wed Nov 02, 2016

]]>The design and synthesis of three-dimensional denser carbons are one of the hot issues in condensed matter physics because of their fascinating properties. Here we identify by *ab initio* calculations several tetragonal and monoclinic polymorphs of carbon that adopt the $t32,t{32}^{*},m32$, and $m{32}^{*}$ struct…

[Phys. Rev. B 94, 174102] Published Wed Nov 02, 2016

]]>The band structure of TaAs provides the necessary conditions for the emergence of Weyl fermions. Measurements verifying this fact are remarkably robust, given the reported levels of nonstoichiometry in typical single crystals. Here we demonstrate the surprising fact that a small degree of nonstoichi…

[Phys. Rev. B 94, 180101(R)] Published Tue Nov 01, 2016

]]>The pressure-induced phase transition of monazite-type ${\mathrm{LaPO}}_{4}$ at $\approx 26$ GPa is studied by single-crystal x-ray diffraction and second harmonic generation (SHG) up to 31 GPa. The structure of the postmonazite phase of ${\mathrm{LaPO}}_{4}$ has been obtained and it is shown that it corresponds to a post-barite-type struc…

[Phys. Rev. B 94, 134109] Published Fri Oct 28, 2016

]]>To investigate the barrier effect of grain boundaries on the propagation of avalanchelike plasticity at the atomic scale, we perform three-dimensional molecular dynamics simulations by using simplified polycrystal models including symmetric-tilt grain boundaries. The cutoffs of the stress-drop distr…

[Phys. Rev. B 94, 140102(R)] Published Tue Oct 25, 2016

]]>In addition to the single polarization-versus-electric field hysteresis loop that is characteristic of ferroelectrics and the double hysteresis loop that is known to occur in antiferroelectrics, a third kind of polarization-versus-electric field function has been reported in several systems. This th…

[Phys. Rev. B 94, 140101(R)] Published Mon Oct 24, 2016

]]>We investigate analytically and numerically the interaction between grain boundaries and second phase precipitates in two-phase coherent solids in the presence of misfit strain. Our numerical study uses amplitude equations that describe the interaction of composition and stress [R. Spatschek and A. …

[Phys. Rev. B 94, 144106] Published Mon Oct 24, 2016

]]>The long-time thermal relaxation of (TMTTF)${}_{2}\mathrm{Br},{\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ and ${\mathrm{Sr}}_{2}{\mathrm{Ca}}_{12}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ single crystals at temperatures below 1 K and magnetic field up to 10 T is investigated. The data allow us to determine the relaxation-time spectrum of the low-energy excitations caused by the charge-density wave or spin-d…

[Phys. Rev. B 94, 144107] Published Mon Oct 24, 2016

]]>The strength of a material can be altered by temperature, pressure, grain size, and orientation distributions. At the microscale, neighboring grains often play important roles in the elastic and plastic deformation process. By applying high pressure to a mixture of germanium and gold powder in the v…

[Phys. Rev. B 94, 144104] Published Fri Oct 21, 2016

]]>We present *ab initio* results for linker decorations in Mg-MOF74, i.e., attaching various metals $\mathcal{M}=\text{Li}$, Na, K, Sc, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Pd, Ag, and Pt near the ring of the linker, creating new strong adsorption sites and thus maximizing small-molecule uptake. We find that in most cases these de…

[Phys. Rev. B 94, 144105] Published Fri Oct 21, 2016

]]>We report a high-pressure study of monoclinic monazite-type $\mathrm{SrCr}{\mathrm{O}}_{4}$ up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with *ab initio* calculations, to find a pressure-induced structural phase transition of $\mathrm{SrCr}{\mathrm{O}}_{4}$ near 8–9 GPa. Evidence of a second phase tr…

[Phys. Rev. B 94, 134108] Published Thu Oct 20, 2016

]]>We study the dynamics of quantum three-level systems due to fast fluctuations of their environment (white noise). As an example, we model the decoherence and dephasing of nitrogen-vacancy (NV) centers in diamond that are positioned near a surface that gives rise to quickly fluctuating magnetic field…

[Phys. Rev. B 94, 134107] Published Wed Oct 19, 2016

]]>A system driven in the vicinity of its critical point by varying a relevant field in an arbitrary function of time is a generic system that possesses a long relaxation time compared with the driving time scale and thus represents a large class of nonequilibrium systems. For such a manifestly nonline…

[Phys. Rev. B 94, 144103] Published Wed Oct 19, 2016

]]>We investigate phase separation including elastic coherency effects in the bulk and at surfaces and find a reduction of the solubility limit in the presence of free surfaces. This mechanism favors phase separation near free surfaces even in the absence of external stresses. We apply the theory to hy…

[Phys. Rev. B 94, 134106] Published Tue Oct 18, 2016

]]>Three extensive density functional/molecular dynamics simulations of the crystallization of amorphous ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ (460 atoms) [Phys. Rev. B **90**, 184109 (2014)] have been completed with simulation times of up to 8.2 ns. Together with the results of earlier simulations with and without a crystallite seed…

[Phys. Rev. B 94, 134105] Published Mon Oct 17, 2016

]]>Thorium and its compounds have received considerable attention in recent years due to the renewed interest in developing the thorium fuel cycle as an alternative nuclear energy technology. There is pressing current need to explore the physical properties essential to the fundamental understanding an…

[Phys. Rev. B 94, 134104] Published Fri Oct 07, 2016

]]>Precipitation of anion nanocrystals (NCs) in initially stoichiometric II-VI crystals under hydrostatic pressure and light exposure is explored by Raman spectroscopy, and the mechanism for this effect is analyzed by model calculations. ZnSe, ZnTe, and CdSe crystals are studied in bulk and/or epitaxia…

[Phys. Rev. B 94, 134102] Published Thu Oct 06, 2016

]]>Strongly scattering elastic media, such as consolidated granular materials, respond to ultrasonic pulse excitations with a long response signal with peculiar properties. The portion of the signal at late times, termed coda, is due to multiple scattering. It contains information about the elastic pro…

[Phys. Rev. B 94, 134103] Published Tue Oct 04, 2016

]]>A hexagonal structure of solid molecular hydrogen with $P{6}_{1}22$ symmetry is calculated to be more stable below about 200 GPa than the monoclinic $C2/c$ structure identified previously as the best candidate for phase III. We find that the effects of nuclear quantum and thermal vibrations play a central ro…

[Phys. Rev. B 94, 134101] Published Mon Oct 03, 2016

]]>We have performed density functional theory (DFT) based calculations for aluminum in extreme conditions of both pressure and temperature, up to five times compressed ambient density, and over 1 000 000 K in temperature. In order to cover such a domain, DFT methods including phonon calculations, quan…

[Phys. Rev. B 94, 144101] Published Mon Oct 03, 2016

]]>A salient feature of cyclically driven first-order phase transformations in crystals is their scale-free avalanche dynamics. This behavior has been linked to the presence of a classical critical point but the mechanism leading to criticality without extrinsic tuning remains unexplained. Here we show…

[Phys. Rev. B 94, 144102] Published Mon Oct 03, 2016

]]>In electromagnetism, acoustics, and quantum mechanics, scattering problems can routinely be solved numerically by virtue of perfectly matched layers (PMLs) at simulation domain boundaries. Unfortunately, the same has not been possible for general elastodynamic wave problems in continuum mechanics. I…

[Phys. Rev. B 94, 100105(R)] Published Fri Sep 30, 2016

]]>The influence of defect dipoles on the electrocaloric effect (ECE) in acceptor doped ${\mathrm{BaTiO}}_{3}$ is studied by means of lattice-based Monte-Carlo simulations using a Ginzburg-Landau type effective Hamiltonian. Oxygen vacancy-acceptor associates are described by fixed local dipoles with orientation parall…

[Phys. Rev. B 94, 094113] Published Thu Sep 29, 2016

]]>Reversible polymorphism of monolayer transition-metal dichalcogenides (TMDC) has currently attracted much attention from both academic and applied perspectives. Of special interest is ${\mathrm{MoTe}}_{2}$, where the stable semiconducting $2H$ and metastable (semi)metallic $1{T}^{\prime}$ phases have a rather small energy differ…

[Phys. Rev. B 94, 094114] Published Thu Sep 29, 2016

]]>An improved thermodynamic cycle is validated in ferroelectric single crystals, where the cooling effect of an electrocaloric refrigerant is enhanced by applying a reversed electric field. In contrast to the conventional adiabatic heating or cooling by on-off cycles of the external electric field, ap…

[Phys. Rev. B 94, 100104(R)] Published Thu Sep 29, 2016

]]>The general method for the calculation of $n\mathrm{th}$ ($n\ge 2$) order elastic constants of the loaded crystal is given in the framework of the nonlinear elasticity theory. For the crystals of cubic symmetry under hydrostatic compression, the two schemes of calculation of the elastic constants of second, third, …

[Phys. Rev. B 94, 104114] Published Thu Sep 29, 2016

]]>The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z metho…

[Phys. Rev. B 94, 094112] Published Wed Sep 28, 2016

]]>We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor ${\left({\mathrm{NbSe}}_{4}\right)}_{3}\mathrm{I}$ by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a well-documented pseudo-Jahn-Teller ferrodistortive structural transition at ${T}_{C}=274$ K, wh…

[Phys. Rev. B 94, 104113] Published Wed Sep 28, 2016

]]>We report on a comprehensive first-principles study of phase stability in the Ni-Al binary, both at zero Kelvin and at finite temperature. First-principles density functional theory calculations of the energies of enumerated orderings on fcc and the sublattices of B2 not only predict the stability o…

[Phys. Rev. B 94, 094111] Published Tue Sep 27, 2016

]]>Despite its fundamental importance in condensed matter physics and geophysical implications, establishing the systematic and direct link between the pressure-induced structural changes in crystalline and noncrystalline low-$z$ oxides and their corresponding evolution in O $K$-edge core-electron excitati…

[Phys. Rev. B 94, 094110] Published Mon Sep 26, 2016

]]>Ferroelectric vortex domains are of significant interest due to their rich physics and potential applications. Here, we propose the crystallographic, strain, and electric conditions for spontaneous vortex domains and study the influence of oxygen octahedral tilt on vortex wall orientations. Using 10…

[Phys. Rev. B 94, 100103(R)] Published Mon Sep 26, 2016

]]>The high-pressure structural and elastic properties of ${\mathrm{MgCO}}_{3},{\mathrm{CaCO}}_{3}$, and $\mathrm{MgCa}{\left({\mathrm{CO}}_{3}\right)}_{2}$ have been investigated with density functional theory. By computing the isotropic elastic constants, we found that the bulk and shear acoustic wave velocities are smaller in carbonates than in their respective silica…

[Phys. Rev. B 94, 104112] Published Fri Sep 23, 2016

]]>We study the effect of electronic Coulomb correlations on the vacancy formation energy in paramagnetic $\alpha \text{\u2212}\mathrm{Fe}$ within *ab initio* dynamical mean-field theory. The calculated value for the formation energy is substantially lower than in standard density-functional calculations and in excellent agreement w…

[Phys. Rev. B 94, 100102(R)] Published Wed Sep 21, 2016

]]>Shock compression of silicon (Si) under extremely high pressures (>100 Mbar) was investigated by using two first-principles methods of orbital-free molecular dynamics (OFMD) and path integral Monte Carlo (PIMC). While pressures from the two methods agree very well, PIMC predicts a second compression …

[Phys. Rev. B 94, 094109] Published Thu Sep 15, 2016

]]>We present an experimental and theoretical study of the optically detected magnetic resonance signals for ensembles of negatively charged nitrogen-vacancy (NV) centers in a ${}^{13}\mathrm{C}$ isotopically enriched single-crystal diamond. We observe four broad transition peaks with superimposed sharp features at ze…

[Phys. Rev. B 94, 094108] Published Wed Sep 14, 2016

]]>Accelerated molecular dynamics reveals a mechanism transition and strong temperature dependence of dislocation nucleation from grain boundaries (GBs) in Cu. At stress levels up to $\sim 90\%$ of the ideal dislocation-nucleation stress, atomic shuffling at the $E$ structural unit in a GB acts as a precursor t…

[Phys. Rev. B 94, 104110] Published Wed Sep 14, 2016

]]>High-temperature atomic configurations of fcc Fe-Cr-Ni alloys with alloy composition close to austenitic steel are studied in statistical thermodynamic simulations with effective interactions obtained in *ab initio* calculations. The latter are done taking longitudinal spin fluctuations (LSF) into con…

[Phys. Rev. B 94, 104111] Published Wed Sep 14, 2016

]]>Using an experimental setup designed to scan a submicron sized light spot and collect the photogenerated current through larger electrodes, we map the photovoltaic response in ferroelectric $\mathrm{BiFe}{\mathrm{O}}_{3}$ single crystals. We study the effect produced by a unique 180° ferroelectric domain wall (DW) and show …

[Phys. Rev. B 94, 094107] Published Mon Sep 12, 2016

]]>Diffusionless displacive lattice rearrangements, which include martensitic transformations, are in real materials often accompanied by a displacive drag of interstitials. The interplay of both processes leads to a particular atomistic arrangement of the interstitials in the product phase, which is d…

[Phys. Rev. B 94, 104109] Published Mon Sep 12, 2016

]]>Two-dimensional (2D) ${\mathrm{BNSi}}_{2}$ has been recently proposed to be a viable candidate material with a graphenelike structure. We have carried out *ab initio* evolutionary ground state searches and uncovered a number of 2D structures in the $\left(\mathrm{BN}\right){}_{x}{\mathrm{Si}}_{1-x}$ pseudobinary system with considerably lower energies. Neve…

[Phys. Rev. B 94, 094105] Published Fri Sep 09, 2016

]]>We explore topological transitions in parameter space in order to enable adiabatic passages between regions adiabatically disconnected within a given parameter manifold. To this end, we study the Hamiltonian of two coupled qubits interacting with external magnetic fields, and make use of the analogy…

[Phys. Rev. B 94, 094106] Published Fri Sep 09, 2016

]]>In this work, a systematic investigation of the alloying behavior on the $M$ sublattice of ${M}_{2}\mathrm{AlC}$, where $M$ is Ti, V, Zr, and Hf with elements in the first transition metal row as well as Ca and Sc is carried out via a combination of alloy theoretic approaches and density functional theory for 41 alloy …

[Phys. Rev. B 94, 104106] Published Fri Sep 09, 2016

]]>The role of quantum ion dynamics in the low melting temperatures of Li is investigated from first principles theory. Free energies of solid and liquid phases are obtained at the classical and quantum ion levels. The results are used to determine the Li melting curve in the 40–60 and 110–150 GPa pres…

[Phys. Rev. B 94, 104107] Published Fri Sep 09, 2016

]]>The exceptionally large piezoelectric response of the morphotropic-phase-boundary (MPB) composition of the lead-free piezoelectric system $(1-x\left)\mathrm{Ba}\right(\mathrm{T}{\mathrm{i}}_{0.8}\mathrm{Z}{\mathrm{r}}_{0.2}){\mathrm{O}}_{3}-x\left(\mathrm{B}{\mathrm{a}}_{0.7}\mathrm{C}{\mathrm{a}}_{0.3}\right)\mathrm{Ti}{\mathrm{O}}_{3}$ has attracted great attention in recent years. Here in this paper we report a detailed investigation of the structural pha…

[Phys. Rev. B 94, 104108] Published Fri Sep 09, 2016

]]>We used *ab initio* random structure searching (AIRSS) to investigate polymorphism in ${\mathrm{C}}_{3}{\mathrm{N}}_{4}$ carbon nitride as a function of pressure. Our calculations reveal new framework structures, including a particularly stable chiral polymorph of space group $P{4}_{3}{2}_{1}2$ containing mixed $s{p}^{2}$ and $s{p}^{3}$ bonding, that we ha…

[Phys. Rev. B 94, 094104] Published Thu Sep 08, 2016

]]>Ferroelectrics that allow a coupling between the polarization and another order parameter are of great interest because they could make the electric field control of nonpolar order parameters possible. In recent years, “hybrid improper’” ferroelectrics - materials where the polarization couples to two different structural distortions - have emerged as a possible way to realize this goal. Theoretical predictions of hybrid improper ferroelectricity in layered perovskite materials were followed by its first experimental realization in Ca${}_{3}$Ti${}_{2}$O${}_{7}$ in 2015. However, the precise pathway by which the polarization reverses in this material during ferroelectric switching remains an open question. The authors address this question and lay the groundwork for understanding the unexpectedly complex domain structure of Ca${}_{3}$Ti${}_{2}$O${}_{7}$, consisting of a network of multiple types of domain walls and topological defects.

[Phys. Rev. B 94, 104105] Published Thu Sep 08, 2016

]]>Spintronics holds the promise of novel functionality and higher device performance, but a massive challenge is to find semiconducting materials with good electronic properties that are also ferromagnetic. Dilute magnetic semiconductors (DMS) such as Mn-doped GaAs have great potential but are notoriously difficult to make, only stabilizing in thin films in most cases. Recently, a promising new class of DMS materials based on the chemistry and structure of iron-based superconductors has been discovered, including the compound (Ba,K)(Zn,Mn)${}_{2}$As${}_{2}$. These materials can be synthesized in bulk form, providing an unprecedented opportunity to study the mechanism of ferromagnetism in semiconductors. In this work, the authors present detailed temperature-dependent characterization of the atomic and magnetic structure of (Ba,K)(Zn,Mn)${}_{2}$As${}_{2}$ using x-ray and neutron pair distribution function techniques, establishing the existence of an unexpected structural distortion on a short length scale and surprisingly robust short-range ferromagnetic correlations that persist even at room temperature. These results fill in important gaps in the experimental understanding of DMS materials and provide valuable guidance to their theoretical description.

[Phys. Rev. B 94, 094102] Published Tue Sep 06, 2016

]]>$\mathrm{G}{\mathrm{e}}_{2}\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{5}$ polycrystalline films either in the trigonal stable phase or in the metastable rock-salt structure have been irradiated with 150 keV ${\mathrm{Ar}}^{+}$ ions. The effects of disorder are studied by electrical, optical, and structural measurements and density functional theory (DFT) simulations. In the met…

[Phys. Rev. B 94, 094103] Published Tue Sep 06, 2016

]]>In general, crystallite size reduction is known to suppress the ferroic order (polarization or magnetization) in ferroelectric and magnetic systems. Using free particles of a giant tetragonality $(c/a\u20131=0.18)$ ferroelectric alloy $\mathrm{BiFe}{\mathrm{O}}_{3}\text{\u2212}\mathrm{PbTi}{\mathrm{O}}_{3}$ as the model system, here we show that the intrinsic size …

[Phys. Rev. B 94, 104104] Published Tue Sep 06, 2016

]]>Polar discontinuity at interfaces plays deterministic roles in charge transport, magnetism, and even superconductivity of functional oxides. To date, most polar discontinuity problems have been explored in heterointerfaces between two dissimilar materials. Here, we show that charged domain walls (CD…

[Phys. Rev. B 94, 100101(R)] Published Fri Sep 02, 2016

]]>Two-dimensional (2D) materials have attracted considerable interest due to their remarkable properties and potential applications for nanoelectronics, electrodes, energy storage devices, among others. However, many well-studied 2D materials lack appreciable conductivity and tunable mechanical streng…

[Phys. Rev. B 94, 104103] Published Fri Sep 02, 2016

]]>Investigation of real two-dimensional systems with Dirac-like electronic behavior under the influence of magnetic field is challenging and leads to many interesting physical results. In this paper we study a 2D graphene model with a particular form of magnetic field as a superposition of a homogeneo…

[Phys. Rev. B 94, 094101] Published Thu Sep 01, 2016

]]>The structural and electronic properties of a series of ${\mathrm{SrMnO}}_{3}$ thin films grown on different substrates leading to different biaxial strains are examined by means of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and electron energy-loss spectroscopy (EE…

[Phys. Rev. B 94, 104101] Published Thu Sep 01, 2016

]]>Molybdenum (Mo) is a transition metal with a wide range of technical applications. There has long been strong interest in its high-pressure behavior, and it is often used as standard for high-pressure experiments. Combining powder x-ray diffraction and dynamic ramp compression, structural and equati…

[Phys. Rev. B 94, 104102] Published Thu Sep 01, 2016

]]>The family of layered ${M}_{n+1}A{X}_{n}$ compounds provides a large class of materials with applications ranging from magnets to high-temperature coatings to nuclear cladding. In this work, we employ a density-functional-theory-based discovery approach to identify a large number of thermodynamically stable ${M}_{n+\mathrm{\dots}}$

[Phys. Rev. B 94, 054116] Published Wed Aug 31, 2016

]]>Synchrotron x-ray diffraction experiments were performed on the network compounds ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_{x}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ at temperatures between 15 and 800 K. The ferroelectric phase of the parent ${\mathrm{BaAl}}_{2}{\mathrm{O}}_{4}$ is largely suppressed by substituting a small amount of Sr for Ba and disappears for $x\ge 0.1$. Structural refinements revea…

[Phys. Rev. B 94, 054117] Published Wed Aug 31, 2016

]]>The monoclinic (M) phases in high-performance relaxor-based ferroelectric single crystals have been recognized to be a vital structural factor for the outstanding piezoelectric property. However, due to the complexity of the structure in M phases, the understanding about it is still limited. In this…

[Phys. Rev. B 94, 054115] Published Mon Aug 29, 2016

]]>The quantum anomalous Hall effect (QAHE) originates from a combination of the spin-orbital coupling and the breaking of time-reversal symmetry due to intrinsic ferromagnetic ordering and was recently observed in Cr and V doped magnetic topological insulators (TIs). However, it was only observed at e…

[Phys. Rev. B 94, 054113] Published Fri Aug 26, 2016

]]>A recent quasielastic neutron scattering (QENS) study of hydrogen in heavily deformed fcc palladium provided the first direct measurement of hydrogen pipe diffusion, which has a significantly higher diffusivity and lower activation barrier than in bulk. While *ab initio* estimates of hydrogen diffusio…

[Phys. Rev. B 94, 054114] Published Fri Aug 26, 2016

]]>Crystal of ${\mathrm{GaV}}_{4}{\mathrm{S}}_{8}$, a multiferroic system hosting a Néel-type skyrmion lattice phase, has been investigated by polarized Raman and IR spectroscopy above and below the ferroelectric phase transition. Counts of the observed IR and Raman-active modes belonging to distinct irreducible representations agr…

[Phys. Rev. B 94, 060104(R)] Published Fri Aug 26, 2016

]]>First-principles simulations of the porous layered calcogenide materials ${\mathrm{Li}}_{2}{\mathrm{SnO}}_{3}$ and ${\mathrm{Li}}_{2}{\mathrm{SnS}}_{3}$ are used to study their structures, Li ion mobilities, and their interactions with excess Li. The pristine materials are characterized by a regular pattern of voids within the calcogenide layers which are oc…

[Phys. Rev. B 94, 064108] Published Fri Aug 26, 2016

]]>We introduce the concept of a *reflection quasilattice*, the quasiperiodic generalization of a Bravais lattice with irreducible reflection symmetry. Among their applications, reflection quasilattices are the reciprocal (i.e., Bragg diffraction) lattices for quasicrystals and quasicrystal tilings, such…

[Phys. Rev. B 94, 064107] Published Thu Aug 25, 2016

]]>The evolution of local ferroelectric lattice distortions in multiferroic ${\mathrm{Ge}}_{1-x}{\mathrm{Mn}}_{x}\mathrm{Te}$ is studied by x-ray diffraction, x-ray absorption spectroscopy, and density functional theory. We show that the anion/cation displacements smoothly decrease with increasing Mn content, thereby reducing the ferroelect…

[Phys. Rev. B 94, 054112] Published Fri Aug 19, 2016

]]>The confinement effect of intercalated atoms in van der Waals heterostructures can lead to interesting interactions between the confined atoms or molecules and the overlaying two-dimensional (2D) materials. Here we report the formation of ordered Cu(100) $p(2\times 2)$ oxygen superstructures by oxygen inter…

[Phys. Rev. B 94, 064106] Published Thu Aug 18, 2016

]]>Computationally-guided material discovery is being increasingly employed using a descriptor-based screening through the calculation of a few properties of interest. A precise understanding of the uncertainty associated with first-principles density functional theory calculated property values is imp…

[Phys. Rev. B 94, 064105] Published Tue Aug 16, 2016

]]>We study a system of particles in two dimensions interacting via a dipolar long-range potential $D/{r}^{3}$ and subject to a square-lattice substrate potential $V\left(\mathbf{r}\right)$ with amplitude $V$ and lattice constant $b$. The isotropic interaction favors a hexagonal arrangement of the particles with lattice constant $a$, wh…

[Phys. Rev. B 94, 054110] Published Mon Aug 15, 2016

]]>We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local moments picture and *ab initio* molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance…

[Phys. Rev. B 94, 054111] Published Mon Aug 15, 2016

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