We study martensitic transformation behavior by considering the coupling of volumetric strain and the transformation strain in a group-subgroup transformation within a Ginzburg-Landau framework. Nonthermoelastic features, including large residual strain, large thermal hysteresis, and incomplete transformation gradually, appear with increasing coupling strength. The volume change associated with the transformation due to the coupling is demonstrated to be the essential physics for nonthermoelastic features that appear in an ideal thermoelastic martensitic transformation. A materials descriptor for features associated with a martensitic transformation is proposed based on insights from the model.

The compound CuTe (vulcanite) undergoes a quasi-one-dimensional charge density wave (CDW) at $T<T_{\mathrm{CDW}}=335$ K with a $5\times 1\times 2$ periodicity. The mechanism at its origin is debated. Several theoretical works claimed that semilocal functionals are unable to describe its occurrence and ascribed its formation only to strong electron-electron interaction. Moreover, the possible role of quantum anharmonicity has not been addressed. Here, by performing quantum-anharmonic calculations, we show that semilocal functionals correctly describe the occurrence of a CDW in CuTe if ultradense electron-momentum grids allowing for small electronic temperatures are used. The distortion is driven by the perfect nesting among one-dimensional Fermi surface sheets extending in the $k_y$ direction. Quantum anharmonic effects are important and tend to suppress both the distortion and $T_{\mathrm{CDW}}$. The quantum anharmonic structural minimization of the CDW phase in the generalized gradient approximation leads, however, to distorted Te-Te bond lengths in the low temperature phase that are $21\%$ of the experimental ones at $T=20$ K. This suggests that, even if the electron-electron interaction is not crucial for the mechanism of CDW formation, it is relevant to accurately describe the structural data for the low-$T$ phase. We assess the effect of electron-electron interaction on the CDW by using the $\text{DFT}+U+V$ approximation with parameters calculated from first principles. We find that electron-electron interaction enhances the Te-Te distortion, $T_{\mathrm{CDW}}$, and the total energy gain by the distortion.

We investigate grain boundaries (GBs) in the cubic inverse Heusler phase ${\mathrm{Fe}}_2\mathrm{CoGa}$ by means of first-principles calculations based on density functional theory. Besides the energetic stability, the analysis focuses on the magnetic properties of a set of 16 GB structures in this intermetallic phase. We determine the integrated excess magnetization across the GB and analyze it in terms of the projected local magnetic moments of the atoms and their local Voronoi volumes. The results are systematically compared to those of corresponding GBs in body-centered-cubic (bcc) Fe. The studied GBs in ${\mathrm{Fe}}_2\mathrm{CoGa}$ may have a considerably increased magnetization at the GB, up to more than twice as much as in bcc Fe, depending on the GB type, while geometrical quantities such as GB widening or local GB excess volume distributions are similar for both phases. We explain this difference by the higher flexibility of the ternary ${\mathrm{Fe}}_2\mathrm{CoGa}$ phase in compensating the disturbance of a crystal defect by structural relaxation. The GB structures therefore have a lower energy accompanied by increased local magnetic moments of the Co and half of the Fe atoms within a distance of a few $\text{Å}$ around the GB plane.

This paper discusses Floquet engineering with arbitrary polarization in $\alpha \text{−}{\mathrm{RuCl}}_3$. We describe the influence of arbitrary polarization and the limiting cases of linear and circular polarization. The corresponding model is derived via perturbation theory up to fourth order. Starting from linear and circular polarization, we bridge the gap between those two limiting cases. We then study more complex Lissajous figures and general trends arising for them. In theory these Lissajous figures should inherit effects from both linear and circular polarized light and therefore yield tuning possibilities not yet explored in the context of candidate Kitaev materials.

In this work, we report low-temperature Raman spectroscopic measurement to investigate the temperature dependence of phonons and magnetic as well as electronic excitations in ${\left({\mathrm{Sm}}_{1-x}{\mathrm{Bi}}_x\right)}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ for $x=0$, 0.02, 0.035, 0.05, and 0.10. A strong spin-phonon coupling induced phonon renormalization is observed below magnetic transition temperature $T_N$ for samples with $x\le 0.035$. An underlying broad continuum attributed to pronounced spin-spin correlations is observed below $T_N$ for pure ${\mathrm{Sm}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$. Significant phonon anomalies at lower temperatures, much below $T_N$, for $x=0$ and 0.02, are observed and are attributed to a possible crossover into the Weyl semimetal state. Most interestingly, we observe clear signatures of quadratic band touching in $x=0.05$ and 0.10 systems in terms of a broad electronic continuum at low temperatures analyzed using the Raman susceptibility for a non-Fermi liquid, corroborating the inference from recent transport measurements.

We characterize the magnetic ground state of the topological kagome metal ${\mathrm{GdV}}_6{\mathrm{Sn}}_6$ via resonant x-ray diffraction. Previous magnetoentropic studies of ${\mathrm{GdV}}_6{\mathrm{Sn}}_6$ suggested the presence of a modulated magnetic order distinct from the ferromagnetism that is easily polarized by the application of a magnetic field. Diffraction data near the Gd-$L_2$ edge directly resolve a $c$-axis modulated spin structure order on the Gd sublattice with an incommensurate wave vector that evolves upon cooling toward a partial lock-in transition. While equal moment (spiral) and amplitude (sine) modulated spin states cannot be unambiguously discerned from the scattering data, the overall phenomenology suggests an amplitude modulated state with moments predominantly oriented in the $ab$ plane. Comparisons to the “double-flat” spiral state observed in Mn-based $R{\mathrm{Mn}}_6{\mathrm{Sn}}_6$ kagome compounds of the same structure type are discussed.

Pair-density waves (PDWs) are superconducting states that spontaneously break translation symmetry in systems with time-reversal symmetry (TRS). Evidence for PDWs has been seen in several recent experiments, as well as in the pseudogap regime in cuprates. Theoretical understanding of PDWs has been largely restricted to phenomenological and numerical studies, while microscopic theories typically require strong coupling or fine tuning. In this work, we provide a symmetry-based mechanism under which PDWs emerge as a weak-coupling instability of a two-dimensional TRS metal. Combining mean-field and renormalization-group analyses, we identify a weak-coupling instability towards a triplet PDW realized in the $\pi$-flux square lattice model with on-site repulsion and moderate nearest-neighbor attraction when the Fermi level crosses Van Hove singularities at 1/4 and 3/4 fillings. This PDW is protected by the magnetic translation symmetries characteristic of Hofstadter systems, of which the $\pi$-flux lattice is a special time-reversal-symmetric case.

We derive the effective $\mathbf{k}·\mathbf{p}$ Hamiltonian for an electron in monolayer $T^{\prime }\text{−}{\mathrm{MoS}}_2$ near the Fermi level in the presence of spin-orbit coupling and a perpendicular electric field. The $4\times 4\mathbf{k}·\mathbf{p}$ Hamiltonian is capable of describing the nonparabolic energy band dispersion, perpendicular electric field effect, and spin texture, in good agreement with first-principles calculations. This $\mathbf{k}·\mathbf{p}$ Hamiltonian provides a simple and convenient way to understand and manipulate the spin transport properties of monolayer $T^{\prime }\text{−}{\mathrm{MoS}}_2$ under the perpendicular electric field. Surprisingly, our model predicts a significantly large out-of-plane spin polarization $\left(S_z\right)$ induced by the charge current along the $x$ direction. We also prove that the mirror symmetry $\left({\sigma }_h\left(yz\right)\right)$ leads to the forbidden of spin polarization $\left(S_z\right)$ induced by the charge current along the $y$ direction.

In this paper, we analyze the band structure of two-dimensional (2D) halide perovskites by considering structures related to the simpler case of the series, (${\mathrm{BA})}_2{\mathrm{PbI}}_4$, in which ${\mathrm{PbI}}_4$ layers are intercalated with butylammonium $[\mathrm{BA}={\mathrm{CH}}_3$(${\mathrm{CH}}_2$)${}_3{\mathrm{NH}}_3]$ organic ligands. We use density-functional-theory (DFT) based calculations and tight-binding (TB) models aiming to discover a simple description of the bands within 1 eV below the valence-band maximum and 2 eV above the conduction-band minimum, which, including the energy gap, is about a $\mathrm{\Delta }E=5$ eV energy range. The bands in this $\mathrm{\Delta }E$ range are those expected to contribute to the transport phenomena, photoconductivity, and light emission in the visible spectrum, at room and low temperature. We find that the atomic orbitals of the butylammonium chains have negligible contribution to the Bloch states which form the conduction and valence bands in the above defined $\mathrm{\Delta }E$ range. Our calculations reveal a rather universal, i.e., independent of the intercalating BA, rigid-band picture inside the above $\mathrm{\Delta }E$ range characteristic of the layered perovskite “matrix” (i.e., ${\mathrm{PbI}}_4$ in our example). Besides demonstrating the above conclusion, the main goal of this paper is to find accurate TB models which capture the essential features of the DFT bands in this $\mathrm{\Delta }E$ range. First, we ignore electron hopping along the $c$ axis and the octahedral distortions and this increased symmetry (from ${\mathrm{C}}_2$ to ${\mathrm{C}}_4$) halves the Bravais lattice unit cell size and the Brillouin zone unfolds to a ${45}^{\circ }$ rotated square and this allows some analytical handling of the 2D TB Hamiltonian. The Pb $6s$ and I $5s$ orbitals are far away from the above $\mathrm{\Delta }E$ range and, thus, we integrate them out to obtain an effective model which only includes hybridized Pb $6p$ and I $5p$ states. Our TB-based treatment (a) provides a good quantitative description of the DFT band structure, (b) helps us conceptualize the complex electronic structure in the family of these materials in a simple way, and (c) yields the one-body part to be combined with appropriately screened electron interaction to describe many-body effects, such as excitonic bound states.

We study transport and relaxation of spinless fermions with long-range Coulomb interactions at high temperatures through numerical simulations of out-of-equilibrium dynamics. We find that the transport and relaxation are continuously slowing down for increasing coupling $V$, and that there is a transition in the type of transport. For intermediate couplings, the system exhibits normal diffusive transport, but the timescale for the onset of that is long. For large couplings, it exhibits subdiffusive transport, while at the same time, the relaxation time diverges exponentially with system lengths, featuring a many-body-localization (MBL)-like phase. We attribute the slow transport to formation of slow bound states and stable clusters of particles. For few-particle systems, we prove the existence, visualize the slowness, and analyze the collision properties of the bound states. For many particles at high densities, there should be a hierarchy of clusters of particles on many different length scales. We argue that at large couplings, the average maximal size of the stable clusters should scale linearly with the length of the lattice, which is in accordance with the MBL-like behavior.

The spin of the conduction-band electrons in a quantum well constitutes a promising two-level system for realizing a quantum bit in the solid state. One of the important parameters in the spin dynamics is their relaxation time. It is desired to develop models and semiconductor structures in order to control it. There are several reported examples of spin lifetime control in quantum wells. Double quantum wells in a semiconductor heterostructure allow the modulation of the relaxation time. By changing the relative thicknesses of the wells in the double quantum well system, the wave function for the lowest-energy level of the conduction band can be distributed symmetrically or asymmetrically with respect to the coupling barrier between the quantum wells to control the Dresselhaus and Rashba components of the spin-orbit coupling and, consequently, the relaxation time. To detect and characterize this effect, circularly polarized photoluminescence was used at low temperatures (19 K). The results reported in the present paper suggest that this coupled double quantum well system enables the design of structures that allows for the control of the relaxation time and the performance of the electron spin as a quantum bit.

The surface optical anisotropy of AlInP(001) surfaces is studied from both experiment and theory. The comparison of the data measured on epitaxially grown ${\mathrm{Al}}_{0.52}{\mathrm{In}}_{0.48}\mathrm{P}\left(001\right)$ epilayers lattice matched to GaAs with spectra calculated for energetically favored AlInP(001) surface structures suggests that the surface is covered with a monolayer of buckled phosphorus dimers, where half of the phosphorus atoms are hydrogen saturated. While the optical anisotropies for photon energies below about 3 eV provide clear fingerprints for the structure of the outermost surface atomic layer, the spectral features at higher energies provide insight into the near surface bulk ordering of AlInP. In particular optical anisotropies at the AlInP critical point energies are found to be related to the CuPt ordering in the material.

Topological insulators hold great promise for dissipationless transport devices due to the robust gapless states inside the insulating bulk gap. So far, several generations of topological insulators have been theoretically predicted and experimentally confirmed, most of them based on three- or two-dimensional materials. Here, on the basis of the first-principles calculations, we predict a quasi-one-dimensional (quasi-1D) topological insulator ${\mathrm{Nb}}_4{\mathrm{SiTe}}_4$ that can be prepared by exfoliation from its three-dimensional bulk phase. This material, characterized by topological ${\mathbb{Z}}_2$ invariants and robust zero-energy edge states, has a large nontrivial gap of $\sim 93.6$ meV, large enough for inhibiting the possibility of the thermal disturbance. Additionally, when applying pressure, we find there is an abnormal force releasing stage originating from the shrinking of the inner Nb atomic rings. In addition, we find that substrate, stacking, defect, and structure deformation have specific effects on electronic properties. Our results reveal a promising quasi-1D topological insulator ${\mathrm{Nb}}_4{\mathrm{SiTe}}_4$ and uncover its unique strain-dependent electronic and mechanical properties.

Recently, near-ambient superconductivity has been experimentally evidenced in a nitrogen-doped lutetium hydride [Nature (London) 615, 244 (2023)], which yields a remarkable maximum $T_c$ of 294 K at just 10 kbar. However, due to the difficulty of x-ray diffraction (XRD) in identifying light elements, such as hydrogen and nitrogen, the crystal structure of the superconductor remains elusive, in particular, for the actual stoichiometry of hydrogen and nitrogen and their atomistic positions. This holds even for its parent structure. Here, we set out to address this issue by performing a thorough density functional theory study on the structural, electronic, dynamical, and optical properties of lutetium hydrides. Through thermal and lattice dynamic analysis as well as XRD and superconductor color comparisons, we unambiguously clarified that the parent structures are a mixture of the dominant ${\mathrm{LuH}}_2$ phase of the ${\mathrm{CaF}}_2$ type (instead of the originally proposed ${\mathrm{LuH}}_3$ structure of the $Fm\overline{3}m$ space group) and the minor LuH phase of the NaCl type.

We numerically study quantum avalanches in one-dimensional disordered spin systems by attaching two XXZ spin chains. One chain has low disorder representing a rare Griffith's region, or thermal inclusion, and the second has larger disorder, i.e., disorder larger than the observed finite-size crossover. Comparing dynamics of this system to identical systems with uniformly large disorder, we find evidence for exponentially slow thermalization (in disorder) within the many-body localized regime when the rare region is present. We observe a decay of the spin imbalance in the bulk of the large disorder region that persists to long times $\left(\sim {10}^4\right)$ and find a universal behavior of the spectral function.

Based on the Bethe ansatz approach and inelastic neutron scattering experiments, we reveal the evolution of confinement of many-body Bethe strings in ordered regions of the quasi-one-dimensional antiferromagnet ${\mathrm{YbAlO}}_3$. In the antiferromagnetic phase, the spin dynamics is dominated by confined length-1 Bethe strings, whose dominancy in the high-energy branch of the excitation spectrum yields to confined length-2 Bethe strings when the material is tuned to the spin-density-wave phase. In the thermal-induced disordered region, the confinement effect disappears, and the system restores the conventional quantum integrable physics of the one-dimensional Heisenberg model. Our results establish a unified picture based on a Bethe string for the spin dynamics in different magnetic phases of ${\mathrm{YbAlO}}_3$, and thus provide profound insight into many-body quantum magnetism.

The performance of superconducting devices is often degraded by the uncontrolled appearance and disappearance of quasiparticles, a process known as poisoning. We demonstrate the electrostatic control of quasiparticle poisoning in the form of single-charge tunneling across a fixed barrier onto a Coulomb island in an InAs/Al hybrid nanowire. High-bandwidth charge sensing was used to monitor the charge occupancy of the island across Coulomb blockade peaks, where tunneling rates were maximal, and Coulomb valleys, where tunneling was absent. Electrostatic gates changed the on-peak tunneling rates by two orders of magnitude for a barrier with fixed normal-state resistance, which we attribute to the gate dependence of the size and softness of the induced superconducting gap on the island, corroborated by separate density-of-states measurements. Temperature and magnetic field dependence of tunneling rates are also investigated.

One-dimensional (1D) chains with nonreciprocal tunneling realizing the non-Hermitian skin effect (NHSE) have attracted considerable interest in the last years, whereas their experimental realization in real space remains limited to a few examples. In this Letter, we propose a generic way of implementing nonreciprocity based on a combination of Rashba-Dresselhauss spin-orbit coupling, existing for electrons, cold atoms, and photons, and a lifetime imbalance between two spin components. We show that one can realize the Hatano-Nelson model, the non-Hermitian Su-Schrieffer-Heeger model, and even observe the NHSE in a 1D potential well without the need for a lattice. We further demonstrate the practical feasibility of this proposal by considering the specific example of a photonic liquid-crystal microcavity. This platform allows one to switch on and off the NHSE by applying an external voltage to the microcavity.