The predictability of molecular dynamics simulations on the plasticity and fracture behaviors of metals is critically dependent on the accuracy of the employed interatomic potential. Here we present an approach to fitting modified embedded-atom method (MEAM) interatomic potentials to several key properties obtained from first-principles calculations and literature data that govern the continuous mechanistic processes in pure unary fcc Ni, Al, and Cu metals. Along with the commonly used lattice and elastic properties, our MEAM potentials are fitted to the cohesive energy curve, the decohesive energy curve, and the generalized stacking fault energy curve, which are the key properties governing the lattice response to volumetric, fracture, and shear deformations. We further demonstrate that these potentials are able to accurately predict the experimental values for a range of other mechanically relevant properties. Importantly, the potentials presented here outperform all existing EAM/MEAM interatomic potentials readily available from the literature and thus enable more accurate simulations of plasticity and fracture behavior of unary fcc metals.

Relaxation processes usually influence the mechanical properties of glassy materials. Recently, a so-called ${\alpha }_2$ relaxation has been identified in metallic glasses, caused by the mobility decoupling between different constituting atoms. It locates between the primary ($\alpha$) relaxation and the secondary ($\beta$) relaxation and behaves as an additional $\alpha$ relaxation. In this paper, we show that ${\alpha }_2$ relaxation influences the yielding behaviors of a model ${\mathrm{Al}}_{90}{\mathrm{Sm}}_{10}$ metallic glass. In particular, the transition from the stress overshoot to nonovershoot yielding and ${\alpha }_2$ relaxation follow the same time-temperature relation and microscopic origin. Our results suggest that ${\alpha }_2$ relaxation provides an additional way to control the mechanical properties of metallic glasses.

First-principles molecular dynamics, within the density functional theory framework, is employed to assess the structural properties of the chalcohalide glass ${\mathrm{Ge}}_{20}{\mathrm{Te}}_{73}{\mathrm{I}}_7$ (gGTI). The calculated total x-ray and neutron structure factors are in quantitative agreement with the experimental counterparts. Glassy gGTI features a predominantly Ge-centered tetrahedral network moderately altered by iodine atoms. Compared to glassy ${\mathrm{Ge}}_{20}{\mathrm{Te}}_{80}$, gGTI shows a substantial decrease in the number of Ge-Te bonds as the presence of I leads to a breaking of the Ge-Te connections and favors the formation of Ge-I terminations where iodine atoms are onefold. Furthermore, we remark a concomitant increase of mixed $\mathrm{Ge}{\mathrm{Te}}_{4-x}{\mathrm{I}}_x$ tetrahedra and $\mathrm{Ge}{\mathrm{Te}}_{3-x}{\mathrm{I}}_x$ trigonal pyramidal units. A minor yet not-negligible fraction of iodine atoms forms Te-I bonds. Breaking of Ge-Te connections and formation of terminal Ge(Te)-I bonds results in a reduced average coordination number associated with an increase of undercoordinated Ge at the expense of fourfold coordinated Ge atoms. The analysis of chains and rings statistics reveals the presence of both linear and cross-linked chains made of Te and five-members rings containing at least one Te-Te or one Ge-Ge homopolar bond.

We study the motion of an impurity in a two-leg ladder interacting with two fermionic baths along each leg, a simple model bridging cold atom quantum simulators with an idealized description of the basic transport processes in a layered heterostructure. Using the linked-cluster expansion, we obtain exact analytical results for the single-particle Green's function and find that the long-time behavior is dominated by an intrinsic orthogonality catastrophe associated to the motion of the impurity in each one-dimensional chain. We explore both the case of two identical legs as well as the case where the legs are characterized by different interaction strengths: In the latter case, we observe a subleading correction which can be relevant for intermediate-time transport at an interface between different materials. In all the cases, we do not find significant differences between the intra- and interleg Green's functions in the long-time limit.

The linear spin-wave theory study of ${\mathrm{PbFeBO}}_4$ spin dynamics is presented. It is shown that the magnetic excitations previously observed in Raman scattering experiments below Néel temperature are optical magnon and two-magnon modes. Based on the magnon energy, two-magnon band line shape, and the Weiss temperature, the consistent set of the exchange coupling constants up to the third-nearest neighbor is derived and compared with the results of ab initio calculations available in the literature. The small deviation of the observed two-magnon band from the one-magnon density of states suggests a surprisingly negligible role of magnon-magnon interactions.

We calculate the current-voltage ($I-V$) characteristic of a Josephson junction containing a resonant level in the weakly coupled regime (resonance width small compared to the superconducting gap). The phase $\varphi$ across the junction becomes time dependent in response to a DC current bias. Rabi oscillations in the Andreev levels produce a staircase $I-V$ characteristic. The number of voltage steps counts the number of Rabi oscillations per $2\pi$ increment of $\varphi$, providing a way to probe the coherence of the qubit in the absence of any external AC driving. The phenomenology is the same as the Majorana-induced DC Shapiro steps in topological Josephson junctions of Choi et al. [Phys. Rev. B 102, 140501(R) (2020)]—but now for a nontopological Andreev qubit.

Electron-phonon superconductors at high pressures have displayed the highest values of critical superconducting temperature $T_c$ on record, now rapidly approaching room temperature. Despite the importance of high-$P$ superconductivity in the quest for room-temperature superconductors, a mechanistic understanding of the effect of pressure and its complex interplay with phonon anharmonicity and superconductivity is missing, as numerical simulations can bring only system-specific details, clouding out key players controlling the physics. Here we develop a minimal model of electron-phonon superconductivity under an applied pressure which takes into account the anharmonic decoherence of the optical phonons. We find that $T_c$ behaves nonmonotonically as a function of the ratio $\mathrm{\Gamma }/{\omega }_0$, where $\mathrm{\Gamma }$ is the optical phonon damping and ${\omega }_0$ is the optical phonon energy at zero pressure and momentum. Optimal pairing occurs for a critical ratio $\mathrm{\Gamma }/{\omega }_0$ when the phonons are on the verge of decoherence (“diffusonlike” limit). Our framework gives insights into recent experimental observations of $T_c$ as a function of pressure in the complex BCS material ${\mathrm{TlInTe}}_2$.

Synthesized $\mathrm{Cu}{\mathrm{Ir}}_2{\left({\mathrm{Te}}_{1-x}{\mathrm{Se}}_x\right)}_4$ samples were comprehensively characterized using various techniques. At ambient pressure, $\mathrm{Cu}{\mathrm{Ir}}_2{\mathrm{Te}}_4$ undergoes an anomalous phase transition at $T_s\sim 250\mathrm{K}$ with a large thermal hysteresis of $\mathrm{\Delta }{T}_s \sim 40\mathrm{K}$ and a superconducting transition at $T_c\sim 3\mathrm{K}$ during magnetization and electrical-resistivity measurements. We determined this transition to be a first-order structural phase transition from high-temperature hexagonal ($P\overline{3}m1$) to low-temperature triclinic ($P\overline{1}$) symmetry. Both external physical pressure and chemical doping largely enhance $T_s$ and $\mathrm{\Delta }{T}_s$ and suppress $T_c$, thereby indicating a strong correlation between $T_s$ and $T_c$. Critically, no superlattice is observed below $T_s$ as per the electron-diffraction examinations. Thus, the anomalous phase transition at $T_s$, which exhibits a large thermal hysteresis in resistivity and magnetization measurements, is structural rather than a charge-density-wave formation.

The relaxation rate for phase transformations depends on how the system is far from its thermodynamic equilibrium. If, for example, temperature in the system approaches to the phase transition point, the relaxation rate becomes close to zero. We theoretically investigate the laser-induced kinetics of chemical order-disorder transformations (CODTs) in substitutional solid alloys at temperatures $T$ satisfying the condition that $|T–T_c|\ll T_c$, where $T_c$ is the CODT critical temperature. In these studies, we use the equation obtained by Metiu, Kitahara, and Ross, that is, $d\eta /dt=–(\mathrm{\Gamma }/2k_{B}T)\partial F/\partial \eta$, where $0<\eta <1$ is the chemical order parameter, Γ is the frequency of atomic jumps, $k_B$ is the Boltzmann constant, and $F$ is the free energy of the system, which we combine with the Landau theory for second-order phase transitions. If the two lowest terms are retained only in a Taylor expansion of $F$, the $\eta \left(t\right)$ dependence can be found analytically. Such an approach is assumed to be valid for sufficiently small $\eta <0.5$. As an example, we simulate CODTs in the thin-film (40-nm thickness) binary alloy of ${\mathrm{Fe}}_x{\mathrm{Al}}_{1-x}$ ($x=0.6$). Our simulations show that both extensive chemical ordering and disordering in the solid alloy are feasible under short-pulse laser irradiation, at least, at a nanosecond time scale. This finding can be useful for improving the properties of functional alloyed materials and for extension of their potential applications.

The origin of the interfacial perpendicular magnetic anisotropy (PMA) induced in the ultrathin Fe layer on the Au(111) surface was examined using synchrotron-radiation-based Mössbauer spectroscopy (MS), x-ray magnetic circular dichroism (XMCD), and angle-resolved photoemission spectroscopy (ARPES). To probe the detailed interfacial electronic structure of orbital hybridization between the Fe $3d$ and Au $6p$ bands, we detected the interfacial proximity effect, which modulates the valence-band electronic structure of Fe, resulting in PMA. MS and XMCD measurements were used to detect the interfacial magnetic structure and anisotropy in orbital magnetic moments, respectively. In situ ARPES also confirms the initial growth of Fe on large spin-orbit coupled surface Shockley states under Au(111) modulated electronic states in the vicinity of the Fermi level. This suggests that PMA in the Fe/Au(111) interface originates from the cooperation effects among the spin, orbital magnetic moments in Fe, and large spin-orbit coupling in Au. These findings pave the way to develop interfacial PMA using $p\text{−}d$ hybridization with a large spin-orbit interaction.

Interacting disordered zigzag graphene nanoribbons have fractional charges, are quasi-one-dimensional, and display an exponentially small gap. Our numerical computations showed that the topological entanglement entropy of these systems has a small finite but universal value, independent of the strength of the interaction and the disorder. The result that was obtained for the topological entanglement entropy shows that the disorder-free phase is critical and becomes unstable in the presence of disorder. Our result for the entanglement spectrum in the presence of disorder is also consistent with the presence of a topologically ordered phase.

The zeroth Landau levels in Weyl semimetals (WSMs) are singular, which result in the anomalous nonsaturated positive longitudinal magnetoconductivity (LMC). The LMC exhibits periodic-in-$1/B$ quantum oscillations attributable to the the oscillating electron density of states in a magnetic field. The intervalley relaxation time ${\tau }^a$ is a key material parameter determining the magnitude of the LMC directly. In existing theories of the LMC, the magnetic field dependence of ${\tau }^a$ is usually neglected. Based upon the Boltzmann equation, we derive analytical expression for the intervalley relaxation time for short-range impurity scattering potential and arbitrary magnetic field strength. Taking the magnetic field dependence of ${\tau }^a$ into consideration, we find that the quantum oscillations of the LMC are enhanced. Numerical calculations are also carried out to verify the analytical derivations. Moreover, we provide an explanation for the anomalous behavior of the LMC observed in WSMs that the amplitude of LMC first increases and then decreases with increasing temperature.

Exchange coupling between localized spins and band or topological states accounts for giant magnetotransport and magneto-optical effects as well as determines spin-spin interactions in magnetic insulators and semiconductors. However, even in archetypical dilute magnetic semiconductors such as ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ and ${\mathrm{Hg}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ the evolution of this coupling with the wave vector $\mathit{k}$ is not understood. For instance, a series of experiments have demonstrated that exchange-induced splitting of magneto-optical spectra of ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ and ${\mathrm{Zn}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ at the $L$ points of the Brillouin zone is, in contradiction to the existing theories, more than one order of magnitude smaller compared to its value at the zone center and can show an unexpected sign of the effective Landé factors, opposite to that found for topological ${\mathrm{Hg}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$. The origin of these findings we elucidate quantitatively by combining (i) relativistic first-principles density functional calculations with the modified Becke-Johnson exchange-correlation potential; (ii) a tight-binding approach that takes carefully into account $\mathit{k}$ dependence of the potential and kinetic $sp-d$ exchange interactions; (iii) a theory of magnetic circular dichroism (MCD) for $E_1$ and $E_1+{\mathrm{\Delta }}_1$ optical transitions, developed here within the envelope function $k·p$ formalism for the $L$ point of the Brillouin zone in zinc-blende crystals. This combination of methods leads to the conclusion that the physics of MCD at the boundary of the Brillouin zone is strongly affected by the strength of two relativistic effects in particular compounds: (i) the mass-velocity term that controls the distance of the conduction band at the $L$ point to the upper Hubbard $d^6$ band of Mn ions and, thus, a relative magnitude and sign of the exchange splittings in the conduction and valence bands; (ii) the spin-momentum locking by spin-orbit coupling that reduces exchange splitting depending on the orientation of particular $L$ valleys with respect to the magnetization direction.

Following a general protocol of periodically driving static first-order topological phases (supporting surface states) with suitable discrete symmetry breaking Wilson-Dirac masses, here we construct a hierarchy of higher-order Floquet topological phases in three dimensions. In particular, we demonstrate realizations of both second-order and third-order Floquet topological states, respectively supporting dynamic hinge and corner modes at zero quasienergy, by periodically driving their static first-order parent states with one and two discrete symmetry breaking Wilson-Dirac mass(es). While the static surface states are characterized by codimension $d_c=1$, the resulting dynamic hinge (corner) modes, protected by antiunitary spectral or particle-hole symmetries, live on the boundaries with $d_c=2\left(3\right)$. We exemplify these outcomes for three-dimensional topological insulators and Dirac semimetals, with the latter ones following an arbitrary spin-$j$ representation.

A condensed-matter platform for analog simulation of complex two-dimensional molecular bonding configurations, based on optically trapped exciton-polariton condensates is proposed. The stable occupation of polariton condensates in the excited states of their optically configurable potential traps permits emulation of excited atomic orbitals. A classical mean-field model describing the dissipative coupling mechanism between $p$-orbital condensates is derived, identifying lowest-threshold condensation solutions as a function of trap parameters corresponding to bound and antibound $\pi$ and $\sigma$ bonding configurations, similar to those in quantum chemistry.

We study theoretically the thermal relaxation of many-body systems under the action of oscillating external fields. When the magnitude or the orientation of a field is modulated around values where the pairwise heat-exchange conductances depend nonlinearly on this field, we demonstrate that the time symmetry is broken during the evolution of temperatures over a modulation cycle. We predict that this asymmetry enables a pumping of heat that can be used to cool the system down faster. This effect is illustrated through different magneto-optical systems under the action of an oscillating magnetic field.

The exact exchange-correlation (xc) kernel $f_{\text{xc}}(x,x^{\prime },\omega )$ of linear response time-dependent density functional theory is computed over a wide range of frequencies for three canonical one-dimensional finite systems. Methods used to ensure the numerical robustness of $f_{\text{xc}}$ are set out. The frequency dependence of $f_{\text{xc}}$ is found to be largely due to its analytic structure, i.e., its singularities at certain frequencies, which are required in order to capture particular transitions, including those of double excitation character. However, within the frequency range of the first few interacting excitations, $f_{\text{xc}}$ is approximately $\omega$ independent, meaning the exact adiabatic approximation $f_{\text{xc}}(\omega =0)$ remedies the failings of the local density approximation and random phase approximation for these lowest transitions. The key differences between the exact $f_{\text{xc}}$ and its common approximations are analyzed, and cannot be eliminated by exploiting the limited gauge freedom in $f_{\text{xc}}$. The optical spectrum benefits from using as accurate as possible an $f_{\text{xc}}$ and ground-state xc potential, while maintaining exact compatibility between the two is of less importance.

Signatures of the excitonic condensation state and its optical properties in biased double-layer graphene (DLG) are discussed. In the framework of the generic bilayer graphene model involving a Coulomb interaction between electrons in one layer and holes in the opposite layer, we have derived a set of self-consistent equations determining the excitonic condensate order parameter by use of the projector-based renormalization method. Based on the Kubo theory of the linear optical response, a formula of the optical conductivity is also obtained with full contributions of the quantum fluctuations. Our results elucidate a possibility of the excitonic condensation formation in the biased system once the dielectric thickness is sufficiently small. As a function of the external electric field, the excitonic condensation dome suppresses rapidly as enlarging the dielectric thickness. The impression of the dielectric thickness and external electric field affecting the excitonic condensate is also addressed in the signature of the optical conductivity. Our findings are worthwhile to understand the formation and stability of the excitonic condensation states not only in DLG but also in other double-layer systems or in semimetal-semiconductor transition materials.

We present a variational matrix product state (vMPS) for the ground state of the spin-1/2 Heisenberg model. The MPS effectively organizes the various dimer configurations, in faithful reflection of the resonating valence bond picture of the spin liquid, with the energy only 0.024% higher than the exact value given by Bethe ansatz. Building on the ground-state vMPS, the one-spin wave function is constructed in a simple manner with the dispersion that matches well with the exact spectrum. The vMPS scheme is applied to the family of Hamiltonian extrapolating between the Heisenberg model and the Majumdar-Ghosh model.