MXenes are a family of two-dimensional (2D) materials composed of transition-metal carbides, nitrides, or carbonitrides and are known for their diverse functional groups that provide good hydrophilicity and electrical conductivity. The electrical properties of these materials have been well explored, but the studies on thermal properties are limited. In this paper, we demonstrate the effect of anharmonic phonon scattering on the thermal properties of this system by analyzing and estimating both explicit and implicit anharmonicity. We analyze the anharmonic behavior of phonons using Raman spectroscopy under varying temperature and hydrostatic pressure conditions. The phonon anharmonicity and the thermal conductivity of multilayer MXene $\mathrm{T}{\mathrm{i}}_3{\mathrm{C}}_2{T}_x$ are probed by analyzing the prominent $A_{1g}$ (Ti, C, O) vibrational mode at 206 $\mathrm{c}{\mathrm{m}}^{-1}$. We find that the temperature and hydrostatic pressure have opposing effects on the $A_{1g}$ (Ti, C, O) vibrational mode, temperature causes a redshift and pressure induces a blueshift. The analysis of temperature- and pressure-dependent Raman spectra, through the estimation of isothermal and isobaric Grüneisen parameters, suggests that the observed main peak (206 $\mathrm{c}{\mathrm{m}}^{-1}$) is primarily dominated by its explicit anharmonicity component over the implicit counterpart. The presence of anharmonicity in $\mathrm{T}{\mathrm{i}}_3{\mathrm{C}}_2{T}_x$ causes phonon-phonon interactions, resulting in a reduced mean-free path. Consequently, the thermal conductivity of as-prepared $\mathrm{T}{\mathrm{i}}_3{\mathrm{C}}_2{T}_x$ MXene is very low ($15.38\pm 0.21 \mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$). This study forms the groundwork for understanding anharmonicity in other 2D MXenes systems.

Twistronics has received much attention as a method to manipulate the properties of two-dimensional van der Waals structures by introducing moiré patterns through a relative rotation between two layers. Here, we begin a theoretical exploration of twistronics beyond the realm of van der Waals materials by developing a first-principles description of the electronic structure and interlayer interactions of ultrathin perovskite bilayers. We construct both an ab initio tight-binding model as well as a minimal three-band effective model for the valence bands of monolayers and bilayers of oxides derived from the Ruddlesden-Popper phase of perovskites, which is amenable to thin-layer formation. We illustrate the approach with the specific example of ${\mathrm{Sr}}_2{\mathrm{TiO}}_4$ layers but also provide model parameters for ${\mathrm{Ca}}_2{\mathrm{TiO}}_4$ and ${\mathrm{Ba}}_2{\mathrm{TiO}}_4$.

The standard paradigm of topological phases posits that two phases with identical symm etries are separated by a bulk phase transition, while symmetry breaking provides a path in parameter space that allows adiabatic connection between the phases. Typically, if symmetry is broken only at the boundary, topological surface states become gapped, and single-particle surface properties no longer distinguish between the two phases. In this work, we challenge this expectation. We demonstrate that the single-particle surface Green's function contains zeros, or “Luttinger surfaces,” which maintain the same bulk-boundary correspondence as topological surface states. Remarkably, these Luttinger surfaces persist under symmetry-breaking perturbations that destroy the surface states. Moreover, we point out that low-energy and surface theories, often used synonymously in discussions of (gapped) topological matter, are actually different, with the difference captured by the Luttinger surfaces.

Nonlocal kinetic energy density functionals (KEDFs) with density-dependent kernels are currently the most accurate functionals available for orbital-free density functional theory (OF-DFT) calculations. However, despite advances in numerical techniques and using only (semi)local-density-dependent kernels, nonlocal KEDFs still present substantial computational costs in OF-DFT, limiting their application in large-scale material simulations. To address this challenge, we propose an efficient framework for reconstructing nonlocal KEDFs by incorporating the density functional tight-binding approach, in which the energy functionals are simplified through a first-order functional expansion based on the superposition of free-atom electron densities. This strategy allows the computationally expensive nonlocal kinetic energy and potential calculations to be performed only once during the electron density optimization process, significantly reducing computational overhead while maintaining high accuracy. Benchmark tests using advanced nonlocal KEDFs, such as revHC and LDAK-MGPA, on standard structures including Li, Mg, Al, Ga, Si, III-V semiconductors, as well as ${\mathrm{Mg}}_{50}$ and ${\mathrm{Si}}_{50}$ clusters, demonstrate that our method achieves orders-of-magnitude improvements in efficiency, providing a cost-effective balance between accuracy and computational speed. Additionally, the reconstructed functionals exhibit improved numerical stability for both bulk and finite systems, paving the way for developing more sophisticated KEDFs for realistic material simulations using OF-DFT.

The development of the protect-annealing method has extended the superconductivity of the electron-doped cuprate ${\mathrm{Pr}}_{1.3-x}{\mathrm{La}}_{0.7}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ (PLCCO) into lower Ce concentrations, while the superconducting volume fraction decreases with underdoping. Employing angle-resolved photoemission spectroscopy with a microfocused beam, we investigated the electronic structure of protect-annealed PLCCO ($x=0.08$) with small superconducting volume fraction. Significant spatial variation of Fermi surface area and shape was observed, suggesting inhomogeneity in electron concentrations and the pseudogap that competes with superconductivity. By performing measurements at dozens of different sample positions, negative and nonmonotonic correlation was found between the electron concentration and pseudogap magnitude. The established correlation illustrates a systematic annealing dependence of the electronic structure where a pseudogap abruptly opens with insufficient oxygen reduction.

Moiré superlattices based on transition metal dichalcogenides (TMDs) exhibit a large nonlinear Hall response under a bias current, far exceeding the performance of their individual constituent layers. This phenomenon has garnered significant attention, though its underlying physics remains a topic of intense debate. Here we systematically investigate the nonlinear Hall effect (NHE) in a twisted bilayer $\mathrm{WS}{\mathrm{e}}_2$ ($\mathrm{tWS}{\mathrm{e}}_2$) device, and uncover its mechanisms through scaling law analysis. The $\mathrm{tWS}{\mathrm{e}}_2$ device demonstrates a pronounced NHE, where the second-harmonic transverse voltage shows a quadratic dependence on the bias current, and reverses its sign when tuned from half filling to full filling of moiré bands. Moreover, applying a larger perpendicular displacement field leads to a rapid decrease of NHE signals. Temperature-dependent measurements and scaling law analysis reveal that the NHE is primarily driven by an intrinsic Berry curvature dipole and extrinsic impurity skew scattering, with the latter often being overlooked in previous studies of twisted TMDs. Our research offers deeper insights into the operating mechanisms of NHE in twisted materials and opens avenues for engineering nonlinear electronics devices.

We study the anisotropic effective mass $m^{*}$ and spin-splitting of the lowest image potential state (IPS1) at W(110) and Ta(110) by combining embedded Green's function calculations and the $\mathbf{k}·\mathbf{p}$ perturbation theory, in which the wave function of IPS1 at nonzero planar wave vector $\mathbf{k}$ is expressed as a superposition of those of the electronic states at $\mathbf{k}=0$ ($\overline{\mathrm{\Gamma }}$). It will be shown that while $m^{*}$ along $\overline{\mathrm{\Gamma }}\overline{\mathrm{H}}$ deviates only modestly from the free-electron mass $m_e, m^{*}$ along $\overline{\mathrm{\Gamma }}\overline{\mathrm{N}}$ can be modified strongly from $m_e$, depending on where the energy of IPS1 at $\overline{\mathrm{\Gamma }}, E_1$, lies relative to the $\sim 1\mathrm{eV}$ wide projection of the unoccupied bulk ${\mathrm{\Sigma }}_4$ band. Furthermore, we reveal that spin orientations of the spin-split IPS1 bands in the presence of spin-orbit interactions are also reversed depending on the relative energetic position of $E_1$ to the projected ${\mathrm{\Sigma }}_4$ band. Since $E_1$ for W(110) lies above, while $E_1$ for Ta(110) lies in the midst of the projected ${\mathrm{\Sigma }}_4$ band, IPS1 of both metals exhibits completely different energy dispersion along $\overline{\mathrm{\Gamma }}\overline{\mathrm{N}}$.

The Harris criterion imposes a constraint on the critical behavior of a system upon introduction of new disorder, based on its dimension $d$ and localization length exponent $\nu$. It states that the new disorder can be relevant only if $d\nu <2$. We analyze the applicability of the Harris criterion to the GKNS network disorder formulated in the paper [I. A. Gruzberg, A. Klümper, W. Nuding, and A. Sedrakyan, Phys. Rev. B 95, 125414 (2017)] and show that the fluctuations of the geometry are relevant despite $d\nu >2$, implying that the Harris criterion should be modified. We have observed that the fluctuations of the critical point in different quenched configurations of disordered network blocks is of order $L^0$, i.e., it does not depend on block size $L$ in contrast to the expectation based on the Harris criterion that they should decrease as $L^{-d/2}$ according to the central limit theorem. Since $L^0>(x-x_c)$ is always satisfied near the critical point, the mentioned network disorder is relevant and the critical indices of the system can be changed. We have also shown that the GKNS disordered network is fundamentally different from Voronoi-Delaunay and dynamically triangulated random lattices: The probability of higher connectivity in the GKNS network decreases in a power law as opposed to an exponential, indicating that we are dealing with a “scale-free” network, such as the internet, protein-protein interactions, etc.

We investigate entanglement detection in quantum materials through criteria based on the simultaneous suppression of collective matter excitations. Unlike other detection schemes, these criteria can be applied to continuous and unbounded variables. By considering a system of interacting dipoles on a lattice, we show the detection of collective entanglement arising from two different physical mechanisms, namely, the ferroelectric ordering and the dressing of matter degrees of freedom by light. In the latter case, the detection shows the formation of a collective entangled phase not directly related to spontaneous symmetry breaking. These results open a new perspective for the entanglement characterization of competing orders in quantum materials and have direct application to quantum paraelectrics with large polariton splittings.

We report on a novel gapless quantum spin liquid in the $S=1$ honeycomb system ${\mathrm{Cu}}_3{\mathrm{LiRu}}_2{\mathrm{O}}_6$ with ${\mathrm{Ru}}^{4+}$ ($4d^4$) where moments remain dynamic down to 50 mK. Heat capacity measurements show no sign of magnetic ordering down to 60 mK inspite of a Curie-Weiss temperature, ${\theta }_{\mathrm{CW}}=-222$ K, indicating a strong antiferromagnetic interaction. In zero field, the magnetic heat capacity $C_m$ shows a linear $T$ dependence with the Sommerfeld coefficient $\gamma =107$ mJ/mol ${\mathrm{K}}^2$, which is much larger than that found in typical Fermi liquids. Our local probe ${}^7\mathrm{Li}$ nuclear magnetic resonance (NMR) measurements find a significant temperature-independent ${}^7\mathrm{Li}$ NMR shift (and hence a nonzero spin susceptibility) at low temperature ($T$) and a linear $T$ variation of the ${}^7\mathrm{Li}$ NMR spin-lattice relaxation rate 1/$T_1$ at low $T$ reminiscent of fermionic excitations. Muon spin relaxation ($\mu \mathrm{SR}$) measurements detect neither long-range ordering nor spin freezing down to 50 mK, and the temperature variation of the muon depolarization rate $\lambda$ shows a gradual increase with decreasing temperature and a leveling off below about 1 K, evincing a persistent spin dynamics common to several spin liquid candidates. Our results provide strong signatures of a quantum spin liquid in the titled honeycomb material.

When a magnetic field is applied in the perpendicular direction to a metallic disk under the action of a radial bias voltage, a tangential electric current superimposes to the radial current due to the presence of the Lorentz force that acts on electrons. Here we introduce a thermal analog of this Corbino effect in many-body systems made of nonreciprocal bodies that interact by exchanging photons in the near-field regime. In systems out of thermal equilibrium with a radial temperature gradient, we demonstrate that the Poynting field in the Corbino geometry is bent in the presence of an external magnetic field, giving rise to a tangential heat flux. This thermomagnetic effect could find applications in the field of thermal management and energy conversion at the nanoscale.

Using first-principles calculations, we studied how the physical configuration of chalcogen vacancies impact the initial step of surface oxidation of two-dimensional transition metal dichalcogenides (TMDs) where the ${\mathrm{O}}_2$ molecule is adsorbed and dissociated into two O atoms. The effects of surface defects on oxidation are studied by calculating the adsorption energies of the ${\mathrm{O}}_2$ molecule and O atoms on the surface as a function of defect size. We showed that the adsorption of ${\mathrm{O}}_2$ on the surface with one or more chalcogen vacancies is thermodynamically more favorable compared to the pristine surface. Furthermore, the stability of adsorption of two O atoms increases with the number of chalcogen vacancies. The calculated projected density of states indicates that the dangling bond (in-gap) states created by the chalcogen vacancies are passivated by the adsorption of O atoms. Oxygen adsorption kinetics calculation shows that there exists a significant energy barrier of about 1 eV for the dissociation of ${\mathrm{O}}_2$ on a surface with only single chalcogen vacancy, whereas a substantially reduced barrier is observed for a surface with two or more vacancies. Our findings suggest that even though vacancy-free two-dimensional (2D) TMDs might not be practically available, the 2D TMD crystals with mainly single chalcogen vacancy defects should be resistant against oxidation and thus provide critical guidance to researchers regarding optimizing the density and clustering of chalcogen vacancies during the crystal growth.

In this paper, we investigate a non-Hermitian Aubry-André-Harper model characterized by power-law hoppings ($1/s^a$) and a quasiperiodic parameter $\beta$, where $a$ denotes the power-law index, $s$ represents the hopping distance, and $\beta$ belongs to the metallic mean family. In the intermediate phases, we find that ergodic states correspond to complex eigenvalues, multifractal states correspond to real eigenvalues, and localized states may exhibit either complex or real eigenvalues. In the localized phase, the energy spectra are complex, with most of the eigenvalues of localized states being real, while a few are complex. Under open boundary conditions, our analysis of fractal dimensions and eigenstates reveals that all ergodic states transform into scale-free localized states. Furthermore, we demonstrate that long-range hoppings weaken the skin effect, offering another perspective for exploring non-Hermitian skin effects.

In this paper, we analytically study phase transitions in quasiperiodically driven one-dimensional quantum critical systems that are described by conformal field theories (CFTs). The phase diagrams and phase transitions can be analytically obtained by using Avila's global theory in one-frequency quasiperiodic cocycles. Compared to previous works where the quasiperiodicity was introduced in the driving time and no phase transitions were observed [Wen et al., Phys. Rev. Res. 3, 023044 (2021)], here we propose a setup where the quasiperiodicity is introduced in the driving Hamiltonians. In our setup, one can observe the heating phases, nonheating phases, and phase transitions. The phase diagram as well as the Lyapunov exponents that determine the entanglement entropy evolution can be analytically obtained. In addition, based on Avila's theory, we prove there is no phase transition in the previously proposed setup of quasiperiodically driven CFTs [Wen et al., Phys. Rev. Res. 3, 023044 (2021)]. We verify our field theory results by studying the time evolution of entanglement entropy on lattice models.

The behavior of the helicity modulus has been frequently employed to investigate the onset of the topological order characterizing the low-temperature phase of the two-dimensional XY model. We here present how the analysis based on the use of this key quantity can be applied to the study of the properties of coupled layers. To this aim, we first discuss how to extend the popular worm algorithm to a layered sample, and in particular to the evaluation of the longitudinal helicity, that we introduce taking care of the fact that the virtual twist representing the elastic deformation one applies to properly define the helicity modulus can act on a single layer or on all of them. We then apply the method to investigate the bilayer XY model, showing how the helicity modulus can be used to determine the phase diagram of the model as a function of temperature and interlayer coupling strength.

A thermal treatment protocol is used to modify the resistance of amorphous GeSbTe compound $\left(a\text{−}\mathrm{GST}\right)$ films. Using consecutive cycles of heating and relaxation, the room temperature resistance of these vacuum-deposited films may be reduced by orders of magnitude while still maintaining their amorphous structure. The main mechanism responsible for the resistance reduction is densification. The modified structure of the $a\text{−}\mathrm{GST}$ during heat treatment is manifested through the time-dependent resistance $R\left(t\right)$ that is monitored concurrently with the sample temperature. The exponential sensitivity of the resistance of these highly disordered systems allows detection of small changes in disorder. These changes can be correlated with modifications observed in electron diffraction experiments. Systematic study of the $R\left(t\right)$ plots generated during heat treatment exposes an auxiliary mechanism that presumably reflects correlations in the system other than nearest-neighbor interactions. The characteristic features of this mechanism, revealed through resistance measurements, herald the appearance of a new element of order in this amorphous compound that has not been detected by conventional structural tools. This illustrates the potential of using transport as a tool for studying fundamental aspects of disorder in glasses.

We consider the spin-1/2 chain material. It was predicted earlier that the intersite spin nematic order can be realized due to the spin-elastic coupling in such a system. Here we show that intersite spin nematic ordered states can be studied using magnetoelastic and magnetoelectric experiments. Intersite spin nematic phases and phase transitions in spin chain materials can be observed in relative changes of the velocity of sound (related to the changes of the elastic modulus of the crystal), the magnetostriction, and, for noncenter-symmetric systems, the electric permittivity as functions of the temperature and the external magnetic field, since those relative changes are proportional to the spin quadrupole (spin nematic) susceptibility of the system.

Magnetic and superconducting properties of the layered superconducting ferromagnet ${\mathrm{CeO}}_{0.5}{\mathrm{F}}_{0.5}{\mathrm{BiS}}_2$ are investigated by specific heat and magnetization measurements and muon spin rotation/relaxation $\left(\mu \mathrm{SR}\right)$. A specific-heat anomaly, an abrupt increase of magnetic susceptibility, and bifurcation of zero-field-cooled and field-cooled magnetization indicate ferromagnetic (FM) order below 7.5 K. Hysteresis loops yield a ${\mathrm{Ce}}^{3+}$ ordered moment of $0.22\left(1\right){\mu }_B$. A low-temperature Schottky specific-heat anomaly indicates a splitting of ${\mathrm{Ce}}^{3+}$ Kramers-doublet ground states, consistent with Orbach-process ${\mathrm{Ce}}^{3+}$ spin dynamics observed in zero-field $\mu \mathrm{SR}$. Transverse-field $\mu \mathrm{SR}$ results indicate bulk superconductivity below $\sim 2$ K and microscopic coexistence of superconductivity and FM order in separate layers. The static local field observed by zero-field $\mu \mathrm{SR}$ in the FM phase is small $(\sim 0.2 \mathrm{mT})$, indicating that ${\mathrm{Ce}}^{3+}$ dipolar fields nearly cancel at muon stopping sites.

We present a locality preserving unitary mapping from fermions to qubits on a two-dimensional torus while accounting for the mapping of topological sectors. Extending the work of Shukla et al. [Phys. Rev. B 101, 155105 (2020)], an explicit intertwiner is constructed in the form of a projected entangled pair operator. By encoding the information about the charge sectors (and if applicable the twisted boundary conditions) in ancillary qubit(s), the intertwiner becomes a unitary operator which exchanges boundary conditions and charge sectors.