Unveiling the principles behind self-organization in quantum systems is of paramount importance, both intrinsically and practically, in view of foreseeable technological applications. Recently, increasing attention has been paid to atomic systems in curved geometries, which are a promising platform for the discovery of new emergent phenomena. A notable example is that of a gas of ultracold atoms loaded into a thin spherical shell, according to a protocol introduced by Zobay and Garraway more than 20 years ago. However, gravity prevents a dilute assembly of atoms from uniformly spreading throughout the shell, which explains why experiments on the condensation and superfluidity of bubble-trapped gases are usually conducted in space under microgravity conditions. In this paper, we focus instead on strongly interacting quantum particles in a bubble trap, choosing the cluster supersolid of soft-core bosons as a testbed. To study the impact of gravity on supersolid order, we consider a gedanken experiment in which the strength of gravity relative to the core repulsion is gradually enhanced. Using path integral Monte Carlo simulations, we trace the parallel evolution of system structure and superfluidity at low temperature, finding that the latter is sizable only when gravity is a small perturbation or, at the other extreme, so strong that particles are all gathered in one cluster at the bottom of the trap. Finally, we assess the relevance of gravity for the equilibrium behavior of ultracold Rydberg-dressed atoms in a bubble trap, concluding that in some cases clues of the supersolid phase in the absence of gravity could be found even in a laboratory on Earth.

The lifetime and intensity of ultrafast luminescence in the near-infrared region were investigated for 15 representative elemental metals: simple light metals (Be, Mg, and Al); $3d$ (Ti, Ni, and Zn), $4d$ (Zr, Mo, Pd, and Sn), and $5d$ (W and Pt) transition metals; and noble metals (Au, Ag, and Cu). The luminescence intensity at 0.9 eV was distributed over a range as wide as 2.5 orders of magnitude. The sum of an instantaneous response and an exponential decay component well approximated the time-evolution of the luminescence intensity at 0.6 eV. The lifetimes obtained from this decomposition were distributed in a narrower range from 110 fs (Be) to 694 fs (Ag), corresponding to a factor 6.3. We proposed a model based on the dielectric function of the bulk metal to understand the luminescence intensity of the quasi-instantaneous component. It was found that the luminescence intensity was inversely proportional to the Drude damping constant, that is, the slower the damping, the stronger the luminescence. This shows that quasi-instantaneous luminescence is quenched by the nonradiative decay of the nonthermal electrons via electron-electron scattering. The electron-phonon (e-ph) coupling strengths were evaluated using Eliashberg functions derived from ab initio calculations, and the decay rates corresponding to e-ph scattering were evaluated using the extended two-temperature model considering the equilibration process of excited electrons. We found fairly good agreement between the experimental and theoretical results for the absolute values of the exponential decay rates.

We study the time evolution of a one-dimensional system of strongly correlated electrons (a “sample”) that is suddenly coupled to a smaller, initially empty system (a “nanoprobe”), which can subsequently move along the system. Our purpose here is to study the role of interactions in this model system when it is far from equilibrium. We therefore take both the sample and the nanoprobe to be described by a Hubbard model with on-site repulsive interactions and nearest-neighbor hopping. We compute the behavior of the local particle density and the local density of states (LDOS) as a function of time using time-dependent matrix product states at quarter and at half filling, fillings at which the chain realizes a Luttinger liquid or a Mott insulator, respectively. This allows us to study in detail the oscillation of the particles between the sample and the nanoprobe. While, for noninteracting systems, the LDOS is time independent, in the presence of interactions, the backflow of electrons to the sample will lead to nontrivial dynamics in the LDOS. In particular, studying the time-dependent LDOS allows us to study how the Mott gap closes locally and how this melting of the Mott insulator propagates through the system in time after such a local perturbation—a behavior that we envisage can be investigated in future experiments on ultrashort time scales or on optical lattices using microscopy setups.

Axis-dependent conduction polarity (ADCP), also referred to as goniopolarity, observed in highly anisotropic materials, presents novel opportunities for the development of transverse electronic devices. The ADCP materials exhibit $p$-type conductivity in one direction and $n$-type conductivity in another. In this study, we introduce a tight-binding (TB) Hamiltonian to capture the essence of this intriguing behavior. This single-band model provides a concise description of ADCP, and it allows for the derivation of the relationship between the shape of the Fermi surface and the type of the doped carriers. Utilizing first-principles calculations, we validate our TB ADCP model in an AA-stacked van der Waals $\mathrm{MoS}{\mathrm{i}}_2{\mathrm{N}}_4$ material, and reveal the origin of the ADCP properties by analyzing its orbital wave function. The observed ADCP is ascribed to the interactions between the $\mathrm{Mo}\_d{z}^2$ orbitals across the $\mathrm{Mo}{\mathrm{N}}_2$ layers, resulting in significantly different Seebeck coefficients with opposite signs when measured along the [100] and [001] directions. Remarkably, we demonstrate that the ADCP in $\mathrm{MoS}{\mathrm{i}}_2{\mathrm{N}}_4$ can be further enhanced by applying a uniaxial compressive strain along the [001] direction. Our findings not only enhance a simplified TB model to understand this fascinating physical phenomenon in a specific material, but also pave the way for innovative strategies to optimize electric transport in the thermoelectric devices leveraging layered materials. This approach holds promise for significant advancements in the design and functionality of next-generation electronic and thermoelectric devices.

The transport across a Kondo-correlated quantum dot coupled to two leads with independent temperatures and chemical potentials is studied using a controlled nonperturbative, and in this sense numerically exact, treatment based on a hybrid numerical renormalization group combined with time-dependent density matrix renormalization group (NRG-tDMRG). In the Kondo regime, for sufficiently large fixed voltage bias $V\gtrsim T_K$, with $T_K$ the Kondo temperature, we find a peak in the conductance vs the temperature gradient $\mathrm{\Delta }T=T_R-T_L$ across left and right lead. Focusing then on zero voltage bias but finite $\mathrm{\Delta }T$ far beyond linear response, we reveal the dependence of the characteristic zero-bias conductance on the individual lead temperatures. We find that the finite-$\mathrm{\Delta }T$ data behaves quantitatively similar to linear response with an effective equilibrium temperature derived from the different lead temperatures. The regime of sign changes in the Seebeck coefficient, signaling the presence of Kondo correlations, and its dependence on the individual lead temperatures provide a complete picture of the Kondo regime in the presence of finite-temperature gradients. The results from the zero-bias conductance and Seebeck coefficient studies unveil an approximate “Kondo circle” in the $T_L/T_R$ plane as the regime within which the Kondo correlations dominate. We also study the heat current and the corresponding heat conductance vs finite $\mathrm{\Delta }T$. We provide a polynomial fit for our numerical results for the thermocurrent as a function of the individual lead temperatures, which may be used to fit experimental data in the Kondo regime.

Weyl semimetals have attracted considerable research interest over the past decade, with a number of intriguing transport phenomena reported. Magnetic Weyl semimetals, which break time reversal symmetry, have been predicted and recently discovered. ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ is a magnetic Weyl semimetal that exhibit a giant anomalous Hall effect (AHE) when the magnetic moments are aligned along the $c$ axis. In this paper, we report the evolution of the AHE with an external magnetic field applied in the $ab$ plane and current along the $c$ axis, namely, the out-of-plane AHE of ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$. Density functional theory calculations predict a finite out-of-plane AHE when the spins are fully aligned in the $ab$ plane. The evolution of the magnetic structure modifies the nodal line distribution and the Berry curvature, resulting in a weaker AHE with an amplitude of $200\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$ at the saturation field. To ensure the alignment of the magnetic field in the $ab$ plane, a two-round scanning process was performed experimentally. After this, the out-of-plane AHE was measured at multiple temperatures. The observed AHE signals with applied fields of 1 and 2 T were in good agreement with theoretical predictions. These results suggest that engineering the anomalous Hall effect may be possible by designing the symmetry relation of the local Berry curvature.

Describing and achieving “unconventional” superconductivity remains a forefront challenge in quantum many-body physics. Here, we use a unitary mapping, combined with the well-established properties of the attractive Hubbard model, to demonstrate rigorously a Hamiltonian with a low-temperature pair-density-wave (PDW) phase. We also show that the same mapping, when applied to the widely accepted properties of the repulsive Hubbard model, leads to a Hamiltonian exhibiting triplet $d$-wave PDW superconductivity and an unusual combination of ferro- and antiferromagnetic spin correlations. We then demonstrate the persistence of the $d$-wave PDW in a Hamiltonian derived from the mapping of the extended $t\text{−}J$ model in the large-$U$ limit. Furthermore, through strategic manipulation of the nearest-neighbor hopping signs of spin-down electrons, we illustrate the attainability of PDW superconductivity at other momenta. The intertwining of different magnetic and exotic pairing correlations noted here may have connections to experimental observations in spin-triplet candidates such as ${\mathrm{UTe}}_2$.

We derive an exact analytical expression, at stroboscopic intervals, for the time-dependent wave function of a class of integrable quantum many-body systems, driven by the periodic delta-kick protocol. To investigate long-time dynamics, we use the wave function to obtain an exact analytical expression for the expectation values of the defect density, magnetization, residual energy, fidelity, and the correlation function after $n\mathrm{th}$ drive cycle. Periodically driven integrable closed quantum systems absorb energy, and the long-time universal dynamics are described by the periodic generalized Gibbs ensemble (GGE). We demonstrate that the expectation values of all observables are divided into two parts: one highly oscillatory term that depends on the drive cycle $n$, and the rest of the terms are independent of it. Typically, the $n$-independent part constitutes the saturation at large $n$ and periodic GGE. The contribution from the highly oscillatory term vanishes in large $n$. We also generalize our formalism to include square-pulse and sinusoidal driving protocols.

We theoretically study the dephasing of an Andreev spin qubit (ASQ) due to electric and magnetic noise. Using a tight-binding model, we calculate the Andreev states formed in a Josephson junction where the link is a semiconductor with strong spin-orbit interaction. As a result of both the spin-orbit interaction and induced superconductivity, the local charge and spin of these states vary as a function of externally controllable parameters: the phase difference between the superconducting leads, an applied magnetic field, and filling of the underlying semiconductor. Concomitantly, coupling to fluctuations of the electric or magnetic environment will vary, which informs the rate of dephasing. We qualitatively predict the dependence of dephasing on the nature of the environment, magnetic field, phase difference between the junction, and filling of the semiconductor. Comparing the simulated electric- and magnetic-noise-induced dephasing rate to experiment suggests that the dominant source of noise is magnetic. Moreover, by appropriately tuning these external parameters, we find sweet spots at which we predict an enhancement in ASQ coherence times.

By using the self-consistent Born approximation, we investigate topological phase transitions in double HgTe quantum wells (QWs) induced by the short-range impurities. Following the evolution of the density of states and the spectral function, we demonstrate multiple closings and openings of the band gap with the increase of the disorder strength due to the mutual inversions between the first and second electronlike and holelike subbands. We show that starting from a band insulator in the clean limit, under the influence of disorder, the double HgTe QW undergoes a transition, first into a semimetal state similar to “bilayer graphene” and then into a high-order topological insulator state with a double band inversion. We find out that all disorder-induced transitions can be fully characterized by introducing a non-Hermitian quasiparticle Hamiltonian encoding the band structure renormalization and quasiparticle decay.

The investigation of intricate alignments in two-dimensional materials has garnered significant attention, fueled by the growing ability to precisely manipulate and engineer electronic properties through controlled stacking and orientation. Recent observations of spontaneous arrangements in multilayer materials with stochastic twist angles offer new opportunities to elucidate the unique physics governing moiré superstructures, and the critical role of the electronic coupling between layers. In this context, the present study focuses on the atomic-scale characterization of nanoporous graphene, with particular emphasis on regions formed by misoriented graphene layers that assemble into crumpled, continuous patterns. Despite the absence of flat domains at the submicron scale, scanning tunneling microscopy is employed to identify dominant twisted multilayer structures in the samples. To complement the experimental observations, a simplified, yet, effective exponential parametric model is introduced, merging independent analytic electron densities to estimate the number of misaligned layers in the scanned areas. This approach is further refined through density-functional theory calculations of projected electron densities from graphene, which are rotated and stacked at adjusted interlayer distances. The synergy between the two models provides a robust framework for distinguishing between twisted bilayer and twisted trilayer domains, as observed in constant-current imaging. Finally, a full density-functional theory analysis is conducted on simple few-layer graphene structures, assessing the role of interlayer correlations. The present study provides an atomic-level description of porous graphene, while also offering accessible tools for simulating twisted layered materials beyond graphene, which may be beneficial for the STM community.

We propose physically reasonable systems capable of avoiding ergodicity at infinite time in the thermodynamic limit, even with generic perturbations and when coupled to a heat bath. In two dimensions, the rainbow loop soup has (stretched) exponentially numerous absolutely stable nonergodic states with diverging energy but vanishing energy density. In three dimensions the rainbow membrane soup has (stretched) exponentially numerous nonergodic states with diverging energy barriers, leading to infinite-time robust ergodicity breaking that even survives coupling to a nonzero temperature heat bath. We describe our results in the language of exact emergent symmetries and demonstrate how the systems avoid common instabilities. Our construction naturally connects to quantum dimer models, topologically ordered systems, the group word construction, and Hamiltonians whose low-energy eigenstates exhibit anomalous entanglement entropy.

We report an observation of a pressure-induced transition from a superconducting (SC) to an insulating (I) phase in single-crystal ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{BiO}}_3$ ($x=0.4,0.43,0.52$, and 0.58) superconductors. X-ray diffraction measurements conducted at 20 K reveal a direct relationship between this SC-I transition and a pressure-induced distortion of crystal structure. With increasing pressure, the lattice parameters $a$ and $c$ of the ambient-pressure superconducting tetragonal (T) phase are compressed continuously below a critical pressure ($P_{c1}$), wherein the pressure $\left(P\right)$ dependence of the superconducting transition temperature ($T_c$) displays a small variation. However, upon further compression, the lattice of the compressed T phase displays an anisotropic change, and $T_c$ shows a monotonous decrease. When the pressure reaches $P_{c2}$ ($P_{c2}>P_{c1}$), the compressed T phase collapses along the $c$ axis, followed by the disappearance of superconductivity and the appearance of the insulating phase. This SC-I transition is fully reversible, with the critical pressure increasing alongside the K doping concentration. These findings are strikingly similar to the SC-I transition observed in hole-doped high-$T_c$ cuprate superconductors under pressure. Identifying their commonalities could deepen our understanding of the mechanisms that underlie high-$T_c$ superconductivity in these two oxide superconductors with a perovskite structure.

The interaction between nonreciprocity and disorder-free localization has emerged as a fascinating open question. Here, we explore the effects of pseudomobility edges along with different types of eigenstates in a one-dimensional lattice subjected to a nonreciprocal finite-height Wannier-Stark ladder. Utilizing the transfer matrix method, we analytically investigate the pseudomobility edges under nonreciprocity, which accurately describes the boundary between ergodic and nonergodic states. The ergodic states, under nonreciprocity, form topological point gaps in the complex plane, with the corresponding eigenstates localized at the boundaries. The localization of mixed states induced by the skin effect and Wannier-Stark ladder is further amplified under nonreciprocity. Through similarity transformations, the fate of multiple eigenstates under nonreciprocal transitions can be captured. Finally, we use wave packet dynamics as a means to detect these emerging states. Our findings broaden the understanding of disorder-free localization in non-Hermitian systems.

Antiferromagnetism, initially considered interesting but useless, recently emerged as one of the most promising magnetic phases for technology. Recently, a low-symmetry antiferromagnetic phase, known as altermagnetic phase, has been discovered, where no time-reversal $\left(\mathcal{T}\right)$ symmetry is observed in spite of a vanishing net magnetization, leading to nondegenerate bands from the opposite magnetic sublattices. In this work, we consider two representatives of orthorhombic $Pnma$ space group, namely, ${\mathrm{BiFeO}}_3$ and ${\mathrm{CaMnO}}_3$, and find the altermagnetic lowest-energy phase in both from our density functional theory calculations. We find a substantial spin-splitting in both systems along a high-symmetry path in the Brillouin zone without considering the spin-orbit interaction (SOI). Detailed features of the band dispersion obtained from our calculation confirm the lifting of sublattice spin degeneracy only in the $k_x=0$ plane while preserving the spin degeneracy in the other planes of the Brillouin zone. We provide a comprehensive symmetry analysis based on the magnetic space group (MSG) to explain our DFT findings and an insightful symmetry-allowed model Hamiltonian, which qualitatively agrees with our results. Additionally, we extend our symmetry analysis to encompass two other potential MSGs within the $Pnma$ space group that may host the spin-splitting phenomenon without considering SOI and the likely form of their Hamiltonian. Our calculations considering SOI reveal weak ferromagnetism in both systems. The detailed studies presented here pave the way for a deeper understanding of the spin-splitting phenomena within the $Pnma$ space group, offering insights into the intricate interplay between symmetry and electronic as well as magnetic properties.

Real-space Bragg coherent x-ray-diffractive imaging unveils the formation of bubble and stripe antiferromagnetic (AFM) phase domains on the surface of ${\mathrm{Ni}}_2{\mathrm{CoTeO}}_6$ single crystal. The stripe domains exhibit dislocation-type topological defects. The defects typically form as defect-antidefect pairs and can be created or annihilated by temperature changes and local heating. Thermal fluctuations of the AFM domain walls are observed near the Néel temperature. Topological defect pairs dynamically form and disappear in the fluctuating state. These observations provide a real-space perspective on the dynamics of the AFM phase transition in a helical antiferromagnet. The remarkable tunability of AFM domain walls in a helical antiferromagnet underscores their potential for AFM spintronics applications.

We examine the entanglement of the ground state of a 16-site spin-$\frac{1}{2}$ pyrochlore cluster in the quantum spin ice regime via various calculations of $\mathcal{I}$ concurrence. Exact ground state solutions to a quantum spin Hamiltonian with four nearest-neighbor exchange parameters were obtained using exact diagonalization. We present results for the ground state $\mathcal{I}$ concurrence in a region within the parameter space of the model where the ground state is a singlet. We discuss variations in the $\mathcal{I}$ concurrence in the context of the composition of the ground state and we demonstrate how a lattice distortion disentangles the state.

Understanding lattice dynamics and thermal transport in crystalline compounds with intrinsically low lattice thermal conductivity (${\kappa }_L$) is crucial in condensed matter physics. In this work, we investigate the lattice thermal conductivity of ${\mathrm{CsCu}}_4{\mathrm{Se}}_3$ by coupling first-principles anharmonic lattice dynamics with a unified theory of thermal transport. Our results reveal that the vibrational properties of ${\mathrm{CsCu}}_4{\mathrm{Se}}_3$ are characterized by strong anharmonicity and wavelike phonon tunneling. At room temperature, the predicted intralayer thermal conductivity is an exceptionally low 0.39 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, markedly lower than the interlayer value of 0.69 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, strikingly challenging the conventional understanding of thermal transport in layered materials. This anomalous phenomenon can be traced back to the substantial coherence contribution along the $z$ axis, driven by the coupling of distinct vibrational eigenstates, which enables efficient thermal transport across layers. Furthermore, the coherence-driven conductivity dominates the total thermal conductivity along the $z$ axis, leading to an anomalous, wide-temperature-range (100–700 K) glasslike thermal transport. We attribute the nonmonotonic temperature dependence of coherence thermal conductivity to the combined effects of anharmonic scattering rates, frequency difference, and phonon renormalization. Our work not only uncovers the microscopic mechanism underlying effective interlayer thermal transport in ${\mathrm{CsCu}}_4{\mathrm{Se}}_3$ but also elucidates the nonmonotonic temperature dependence of thermal conductivity, offering valuable insights into the anomalous heat transport in layered compounds.