Few-layer quantum materials, such as transition-metal dichalcogenides (TMDs), are paving the path to the design of high-efficiency devices in the field of microelectronics and optoelectronics. However, heterostructures of quantum materials coming from different families, while they would immensely broaden the range of possible applications, remain challenging. Here, we demonstrate the large-scale integration of compounds from two highly multifunctional families: the three-dimensional conventional semiconductor GaP and the two-dimensional TMD semiconductor ${\mathrm{WSe}}_2$ which is particularly interesting in terms of its potential for electronic, spintronic, and photonics applications. We show that a 2H-2H (or AA′A) trilayer of ${\mathrm{WSe}}_2$ can be grown by molecular-beam epitaxy (MBE) onto gallium phosphide (GaP) substrate. A sharp, high-quality ${\mathrm{WSe}}_2$-GaP interface was confirmed by scanning high-resolution transmission electron microscopy and x-ray photoemission spectroscopy. We present a combined experimental and theoretical study of the structure of the valence band of trilayer ${\mathrm{WSe}}_2$. Nanoangle-resolved photoemission spectroscopy and density-functional theory calculation show that trilayer electrons populate two distinct subbands associated with the K and Γ valleys, with effective masses along the ΓM direction about 0.27 and $0.5m_{\mathrm{e}}$, respectively ($m_{\mathrm{e}}$ is the bare electron mass).

The frustrated ladder with alternate ferromagnetic exchange $-J_F$ and antiferromagnetic exchange $J_A$ to first neighbors and ferromagnetic exchange $-J_L$ to second neighbors is studied by exact diagonalization and density matrix renormalization group calculations in systems of $2N$ spins-$\frac{1}{2}$ with periodic boundary conditions. The ground state is a singlet $(S=0)$ and the singlet-triplet gap ${\varepsilon }_T$ is finite for the exchanges considered. Spin-$\frac{1}{2}$ string correlation functions $g_1\left(N\right)$ and $g_2\left(N\right)$ are defined for an even number $N$ of consecutive spins in systems with two spins per unit cell; the ladder has string order $g_2\left(\infty \right)>0$ and $g_1\left(\infty \right)=0$. The minimum $N^{*}$ of $g_2\left(N\right)$ is related to the range of ground-state spin correlations. Convergence to $g_2\left(\infty \right)$ is from below, and $g_1\left(N\right)$ decreases exponentially for $N\ge N^{*}$. Singlet valence bond (VB) diagrams account for the size dependencies. The frustrated ladder at special values of $J_F, J_L$, and $J_A$ reduces to well-known models such as the spin-1 Heisenberg antiferromagnet and the $J_1\text{−}{J}_2$ model, among others. Numerical analysis of ladders matches previous results for spin-1 gaps or string correlation functions and extends them to spin-$\frac{1}{2}$ systems. The nondegenerate singlet ground state of the ladder is a bond-order wave, a Kekulé VB diagram at $J_L=J_F/2\le J_A$, that is reversed on interchanging $-J_F$ and $J_A$. Inversion symmetry is spontaneously broken in the dimer phase of the $J_1\text{−}{J}_2$ model where the Kekulé diagrams are the doubly degenerate ground states at $J_2/J_1=1/2$.

Recent Josephson tunneling experiments on twisted flakes of high-$T_c$ cuprate superconductor ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+x}$ revealed a nonreciprocal behavior of the critical interlayer Josephson current, i.e., a Josephson diode effect. Motivated by these findings we study theoretically the emergence of the Josephson diode effect in twisted interfaces between nodal superconductors, and highlight a strong dependence on the twist angle $\theta$ and damping of the junction. In all cases, the theory predicts diode efficiency that vanishes exactly at $\theta ={45}^{\circ }$ and has a strong peak at a twist angle close to $\theta ={45}^{\circ }$, consistent with experimental observations. Near ${45}^{\circ }$, the junction breaks time-reversal symmetry $\mathcal{T}$ spontaneously. We find that for underdamped junctions showing hysteretic behavior, this results in a dynamical Josephson diode effect in a part of the $\mathcal{T}$-broken phase. The direction of the diode is trainable in this case by sweeping the external current bias. This effect provides a sensitive probe of spontaneous $\mathcal{T}$ breaking. We then show that explicit $\mathcal{T}$-breaking perturbations with the symmetry of a magnetic field perpendicular to the junction plane lead to a thermodynamic diode effect that survives even in the overdamped limit. We discuss an experimental protocol to probe the double-well structure in the Josephson free energy that underlies the tendency towards spontaneous $\mathcal{T}$ breaking even if $\mathcal{T}$ is broken explicitly. Finally, we show that in-plane magnetic fields can control the diode effect in the short junction limit, and predict the signatures of explicit $\mathcal{T}$ breaking in Shapiro steps.

The high-pressure–high-temperature behavior of tin has been measured with x-ray diffraction and laser-heated diamond anvil cells up to 225 GPa at 300 K and to 110 GPa and $\sim 4000$ K. Temperature has been measured using conventional point pyrometry as well as a four-color mapping pyrometer. The stability fields of Sn liquid and solid phases $(\beta \text{−}\mathrm{Sn}, \mathrm{bct} \gamma \text{−}\mathrm{Sn}, \mathrm{bcc}\text{−}\mathrm{Sn}, \mathrm{hcp}\text{−}\mathrm{Sn})$ have been constrained. The high-pressure hcp-Sn phase has been observed but at higher pressure than under hydrostatic compression. The bcc-bct transition conditions are measured, up to a bcc-bct-liquid triple point at 18.9 GPa/1410 K. A lower bound for bcc-Sn melting line is proposed (Simon equation): $T_m=581{((P-2.86)/6.44+1)}^{0.71}$ ($P$ in GPa, $T_m$ in Kelvin).

Initial conditions after quenching from a high-temperature paraelectric phase to a low-temperature ferroelectric phase have a substantial impact on the temporal development and formation of stable polarization domain structures which eventually determine physical properties and the functionality of ferroelectrics. Based on the recently advanced exactly solvable model of the stochastic domain structure kinetics in a uniaxial ferroelectric [Phys. Rev. B 107, 144109 (2023)], we study the effect of the magnitude of the initial disorder, its initial correlation length, and polarization correlation function on the system evolution. For different shapes of the initial correlation function, the time-dependent correlation length and the two-point polarization correlation coefficient are calculated analytically, demonstrating universal features and good agreement with the available experimental data. Particularly, the magnitude of the charge density correlation function reveals a strong reduction of the bound charges at the nominally charged domain walls which was recently observed experimentally in uniaxial ferroelectrics. Consequently, the integrodifferential equations of evolution for the polarization correlation function and the mean polarization are numerically solved for different initial conditions. The temporal dependence of the polarization mean value and variance are evaluated, demonstrating the bifurcation behavior depending on the applied electric field. The impact of the initial state properties on the coercive field deciding between the single- and multidomain final states of the system is disclosed.

The dynamics of defect excitations in crystalline solids is necessary to understand the macroscopic low-energy properties of elastic media. We use fracton-elasticity duality to systematically study the defect dynamics and interactions in the linear isotropic medium. We derive the explicit expressions for the dual gauge potentials for moving dislocations and the resulting Jefimenko equations. We also compute stresses and strains. The paper includes two physical situations: when the vacancy number is fixed and when the number is fluctuating. If defects are present we show a constraint that needs to be satisfied by them when they climb perpendicularly to their Burgers vector. Next, we extend the classic result of Peach and Koehler for the force between two dislocations and show that, similarly to moving charges in electrodynamics, it is nonreciprocal, when one dislocation is moving. We argue that our formalism can be extended beyond Cauchy's elasticity by exploiting the simplifications provided by the dual gauge formulation of elastic stresses.

We investigate the impacts of an imaginary transverse field on the dynamics of magnetic domain walls in a quantum Ising chain. We show that an imaginary field plays a similar role as a real transverse field in forming a low-lying Wannier-Stark ladder. However, analytical and numerical calculations of the time evolutions in both systems show that the corresponding Bloch oscillations exhibit totally different patterns for the same initial states. These findings reveal the nontrivial effect of non-Hermiticity on quantum spin dynamics.

We present an ab initio study of neutral core and valence electronic excitations in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$ by solving the Bethe-Salpeter equation (BSE) of many-body perturbation theory within an all-electron framework. Calculated spectra at the Al K and $L_1$ edges are in remarkable agreement with available experiments from x-ray absorption (XAS) and x-ray Raman spectroscopy once excitonic effects are taken into account. The combination of the BSE spectra for the two techniques confirms the dipole-forbidden nature of the exciton prepeak as suggested by recent calculations based on density-functional theory. Moreover, we make predictions for resonant inelastic x-ray scattering (RIXS) spectra at K and $L_1$ edges, which strikingly fully overlap also beyond an independent-particle picture. The RIXS calculations reveal two distinct regimes as a function of incoming photon energy. Below and at the XAS threshold, we observe Raman-like features, characterized by strong excitonic effects, which we directly compare to peaks in the loss function. Above the XAS threshold, instead, fluorescence features become predominant: RIXS spectra can be well described and analyzed within an independent-particle approximation showing similarity with the x-ray emission spectrum.

We present a study on the long-term evolution of a non-Hermitian one-dimensional system with on-site dissipations in quantum-walk dynamics. By investigating various cases, including different evolution operations, lattice sizes, initial positions, and dissipations, we uncover remarkable and unconventional features. They include the emergence of distinct final states after a sufficiently long evolution time, the persistence of metastable states for extended periods, the survival of extended states only within the inner region of a domain-wall structure, and the occurrence of instantaneous ultrafar jumps during the evolution process. To provide insight into the underlying physical mechanisms behind these observations, we undertake a comprehensive investigation accompanied by detailed analysis, clarify the relation between time-evolved (meta)stable states and system eigenstates, and analyze the symmetry of final states. Moreover, our research reveals some phenomena that differ from those seen in previous experimental results, which can be attributed to the limited evolution time in the experiments. These theoretical findings underscore the significance of long-term evolution in non-Hermitian systems based on quantum walks.

The dielectric properties of thin films are of paramount importance in a variety of technological applications, and of fundamental importance for solid-state research. In spite of this, there is currently no theoretical understanding of the dependence of the dielectric permittivity on the thickness of thin films. We develop a confinement model within the Lorentz-field framework for the microscopic Langevin-equation description of dielectric response in terms of the atomic-scale vibrational modes of the solid. Based on this, we derive analytical expressions for the dielectric permittivity as a function of thin-film thickness, in excellent agreement with the experimental data of barium-strontium-titanate thin films of different stoichiometry. The theory shows that the decrease of dielectric permittivity with decreasing thickness is directly caused by the restriction in $k$ space of the available eigenmodes for the field-induced alignment of ions and charged groups.

We investigate the development and tuning of resonant optical effects in finite-size periodic arrays (metasurfaces) of silicon nanoparticles. By applying Green's tensor formalism and the coupled dipole approximation while incorporating electric and magnetic dipole moments, we outline a theoretical framework to model the optical response of such nanoparticle arrays. We consider the resonant optical response of finite-size arrays as a function of the nanoparticle (unit cell) number in two distinct scenarios of collective resonances: the lattice resonant Kerker effect, which is a complete suppression of the backward scattering, and the quasi-bound state in the continuum. Our developed models and findings provide a pathway for extracting crucial details about the lattice period and the required array size for the experimental observation of collective resonances. These resonances are typically predicted under the assumption of an infinite periodic lattice. By bridging the theoretical predictions with practical considerations, our results contribute to better understanding of specific conditions needed to experimentally observe these collective resonances in finite-size arrays.

The operator growth hypothesis (OGH) is a technical conjecture about the behavior of operators—specifically, the asymptotic growth of their Lanczos coefficients—under repeated action by a Liouvillian. It is expected to hold for a sufficiently generic closed many-body system. When it holds, it yields bounds on the high-frequency behavior of local correlation functions and measures of chaos (like OTOCs). It also gives a route to numerically estimating response functions. Here we investigate the generalization of OGH to open quantum systems, where the Liouvillian is replaced by a Lindbladian. For a quantum system with local Hermitian jump operators, we show that the OGH is modified: we define a generalization of the Lanczos coefficient and show that it initially grows linearly as in the original OGH, but experiences exponentially growing oscillations on scales determined by the dissipation strength. We see this behavior manifested in a semi-analytically solvable model (large-$q$ SYK with dissipation), numerically for an ergodic spin chain, and in a solvable toy model for operator growth in the presence of dissipation (which resembles a non-Hermitian single-particle hopping process). Finally, we show that the modified OGH connects to a fundamental difference between Lindblad and closed systems: At high frequencies, the spectral functions of the former decay algebraically, while in the latter they decay exponentially. This is an experimentally testable statement, which also places limitations on the applicability of Lindbladians to systems in contact with equilibrium environments.

Carrier mobility is an essential parameter of semiconductors, characterizing how quickly carriers can move in a material when driven by an external electric field. Because electron-phonon (e-ph) scattering limits the room-temperature carrier mobility in high-quality semiconductors, understanding the mechanisms of interaction between carriers and phonons at the microscopic level is vital to investigate the transport properties, especially in nanoelectronic devices. Here, we reproduce the experimentally measured electron and hole mobility in silicon (Si) over a wide temperature range without relying on adjustable parameters by performing the first-principles calculations. By decomposition of the first-principles calculation-predicted e-ph scattering into the contributions from different phonon modes and electronic valleys, we show that the transverse acoustic (TA) phonon mode has a comparable contribution to the longitudinal acoustic (LA) phonon mode in scattering of both electrons and holes on limiting the carrier mobilities in Si. This is in striking contrast with the common sense that the TA mode is negligible based on the classical e-ph interaction modes. We unravel that the neglect of TA scattering is due to the substantial underestimation of the shear deformation potential (associated with the TA mode) with respect to the dilation deformation potential (associated with the LA mode). We also find that the transverse optical (TO) phonon mode, rather than the conventionally presumed longitudinal optical (LO) and LA modes, provides the leading scattering channel (accounting for 58%) in $f$-type intervalley scattering and the LO mode is dominant over the LA mode in $g$-type intervalley scattering for electrons in Si. These findings illustrate why the technology computer-aided design device simulation loses the predictive capability, although it is possible to obtain reasonable results using adjustable parameters based on the incorrect physics models. It calls for a revisit of the mechanisms underlying the carrier mobility in semiconductors.

Monolayers of transition metal dichalcogenides (TMDC) became one of the most studied nanostructures in the last decade. Combining two different TMDC monolayers results in a heterostructure whose properties can be individually tuned by the twist angle between the lattices of the two van der Waals layers and the relative placement of the layers, leading to moiré cells. For small twist angles, lattice reconstruction leads to strong strain fields in the moiré cells. In this paper, we combine an existing theory for lattice reconstruction with a quantum dynamic theory for interlayer excitons and their dynamics due to exciton-phonon scattering using a polaron transformation. The exciton theory is formulated in real space instead of the commonly used quasimomentum space to account for imperfections in the heterolayer breaking lattice translational symmetry. We can analyze the structure of the localized and delocalized exciton states and their exciton-phonon scattering rates for single phonon processes using Born-Markov approximation and multiphonon processes using a polaron transformation. Furthermore, linear optical spectra and exciton relaxation Green's functions are calculated and discussed. A P-stacked ${\mathrm{MoSe}}_2/{\mathrm{WSe}}_2$ heterolayer is used as an illustrative example. It shows excitons localized in the potential generated through the moiré-pattern and strain and a delocalized continuum. The exciton-phonon relaxation times vary depending on the strain and range from subpicoseconds up to nanoseconds.

We present the structural evolution and electrical transport properties in quasi-two-dimensional layered ${\mathrm{CeTe}}_3$ under high pressures by employing Raman spectra, synchrotron x-ray diffraction (XRD), and electrical resistance measurements. Our Raman and XRD experiments reveal the suppression of charge density wave (CDW) occurring via two distinct ways at ∼6 GPa in different hydrostatic environments, namely, incommensurate-to-commensurate transition via the distortion of the Te sheets at quasihydrostatic condition and the transformation from the superlattice of the Cmcm structure to an intermediate phase (HP I) with lower symmetric structure at nonhydrostatic condition. The electrical transport measurements show the emergence of the superconductivity (SC) at ∼3.3 GPa after suppression of CDW and antiferromagnetism. Upon further compression up to ∼90 GPa, the low-pressure layered structure transforms into a high-pressure phase (HP II) with three-dimensional structure, which is tentatively attributed to the Pmmn symmetry and accompanied by a new superconducting behavior. Our discoveries shed light on the distinct mechanisms in pressure-induced suppression of CDW and transformation from the layered to three-dimensional structure in the rare-earth tritelluride family.

In a previous work [M. Hodapp and A. Shapeev, Mach. Learn.: Sci. Technol. 1, 045005 (2020)], we proposed an algorithm that fully automatically trains machine-learning interatomic potentials (MLIPs) during large-scale simulations, and successfully applied it to simulate screw dislocation motion in body-centered-cubic tungsten. The algorithm identifies local subregions of the large-scale simulation region where the potential extrapolates, and then constructs periodic configurations of 100–200 atoms out of these nonperiodic subregions that can be efficiently computed with plane-wave density functional theory (DFT) codes. In this work, we extend this algorithm to dissociated dislocations with arbitrary character angles and apply it to partial dislocations in face-centered-cubic aluminum. Given the excellent agreement with available DFT reference results, we argue that our algorithm has the potential to become a universal way of simulating dissociated dislocations in face-centered-cubic and possibly other materials, such as hexagonal-closed-packed magnesium, and their alloys. Moreover, it can be used to construct reliable training sets for MLIPs to be used in large-scale simulations of curved dislocations.