By using unbiased determinant quantum Monte Carlo simulations, we investigate the interplay between superconductivity and charge density wave order in the Holstein model on a honeycomb lattice with next-nearest-neighbor hopping $t^{\prime }$. We find that a finite negative $t^{\prime }$ enhances $s$-wave superconducting pairing susceptibility near the van Hove fillings in the weak electron-phonon coupling regime, while it suppresses superconductivity and promotes charge density wave order at intermediate electron-phonon coupling strengths. The effect of $t^{\prime }$ on a charge density wave is filling dependent: it suppresses the charge density wave at half filling but enhances it near the van Hove singularities. A Spectral analysis reveals the opening of a gap at low temperatures, highlighting the competitive relationship between superconducting and charge density wave orders mediated by electron-phonon coupling and tuned by $t^{\prime }$.

The thermodynamics of ordered and disordered carbon vacancy structures in ZrC are investigated using ab initio methods. A density functional theory (DFT) study of low-temperature ordered structure energetics identifies three new structures on the convex hull—${\mathrm{Zr}}_{12}{\mathrm{C}}_{11}$ (C2/m), ${\mathrm{Zr}}_9{\mathrm{C}}_8$ ($\mathrm{R}\overline{3}$), and ${\mathrm{Zr}}_6{\mathrm{C}}_5$ ($\mathrm{P}\overline{1}$)—in addition to structures proposed from previous works—${\mathrm{Zr}}_7{\mathrm{C}}_6$ ($\mathrm{R}\overline{3}$), ${\mathrm{Zr}}_4{\mathrm{C}}_3$ (C2/c), ${\mathrm{Zr}}_3{\mathrm{C}}_2$ (Fddd), and ${\mathrm{Zr}}_2\mathrm{C}$ ($\mathrm{Fd}\overline{3}\mathrm{m}$). The phase diagram of ordered structures and their transition to disorder is examined using grand-canonical Monte Carlo simulations and cluster expansions parametrized on a DFT database of electron cold and vibrational harmonic free energies for a variety of vacancy structures. Most of the ordered structures identified undergo first-order transition to the disordered phase at or below 1000 K, with the exception of ${\mathrm{Zr}}_2\mathrm{C}$, which is second order in transition and stable to moderate temperatures ($\sim 1500\mathrm{K}$) as well as broad carbon-to-metal ratios ($x=0.5\text{–}0.65$). The exceptional stability of ${\mathrm{Zr}}_2\mathrm{C}$ provides a rationale for it being the only conclusively observed ordered structure experimentally. Thermodynamics from the Monte Carlo simulations are combined with higher-temperature free energetics effects, vibrational anharmonicity, and electronic thermal excitation, which are computed from DFT molecular dynamics. These effects are found to be appreciable above 1500 K and are on an equal footing with electron cold and vibrational harmonic effects in governing the stability of vacancies. Computed thermodynamic values are in accord with available experimental thermodynamics of carbon-depleted structures. The equilibrium vacancy concentration derived from the calculations agrees with an existing, experimentally derived thermodynamic model except at low temperatures, where experimental data are limited and the computations suggest lower vacancy concentrations. The results run counter to previous computational studies showing significantly more vacancies than expected from experiments. In summary, this work enhances our understanding of both the phase diagram and vacancy stability of ZrC, ultimately providing data that can be leveraged to guide future experimental and theoretical investigations of vacancy structures and thermodynamics.

In trapped-ion quantum simulators, effective spin-1/2 XY interactions can be engineered via laser-induced coupling between internal atomic states and collective phonon modes. In the simplest one-dimensional ($1\text{D}$) traps, these interactions decay as a power-law with distance $1/r^{\alpha }$, with a tunable exponent $\alpha$. For small $\alpha$, the resulting long-range 1D XY model exhibits continuous symmetry breaking, in marked contrast to its nearest-neighbor counterpart. In this paper, we examine this model near the phase transition at ${\alpha }_c$ from the lens of the spin stiffness, or superfluid density. We develop a stochastic series expansion quantum Monte Carlo (QMC) simulation and a generalized winding number estimator to measure the superfluid density in the presence of power-law interactions, which we test against exact diagonalization for small lattice sizes. Our results show how conventional superfluidity in the 1D XY model is enhanced in the long-range interacting regime. This is observed as a diverging superfluid density as $\alpha \to 0$ in the thermodynamic limit, which we show is consistent with linear spin-wave theory. Finally, we define a normalized superfluid density estimator that clearly distinguishes the short-, medium-, and long-range interacting regimes, providing a novel QMC probe of the critical value ${\alpha }_c$.

As a technologically important class of materials, group-IIIA oxides $M_2{\mathrm{O}}_3$ ($M$ = Al, Ga, In) have been extensively applied in various areas, yet their polaronic nature of self-trapped excess charge remains controversial. Here, utilizing the recently developed first-principles theory of polarons, we investigate the formation of hole polarons in $M_2{\mathrm{O}}_3$ to clarify whether they are small or large. We consider the most common rhombohedral and monoclinic phases of $M_2{\mathrm{O}}_3$ and reveal that an excess hole forms a highly anisotropic large polaron in rhombohedral ${\mathrm{Al}}_2{\mathrm{O}}_3$, while it also forms a large polaron in monoclinic ${\mathrm{Al}}_2{\mathrm{O}}_3$ but with much weaker anisotropy. For ${\mathrm{Ga}}_2{\mathrm{O}}_3$, our calculations confirm the formation of a small polaron in monoclinic phase, but a large polaron is more favorable in rhombohedral phase. In rhombohedral ${\mathrm{In}}_2{\mathrm{O}}_3$, the hole is found to exhibit as a large polaron with an ellipsoid feature. The drastically different polaronic characteristics in $M_2{\mathrm{O}}_3$ are explained in terms of the distinct electronic band structures and phonon spectra. This work not only clarifies the existing controversies between the available theoretical calculations and experimental observations, but it also sheds light on the potential applications of oxide materials with diverse functionalities.

The oxygen-related photoluminescence (PL) centers in $4H$-SiC comprise promising solid-state quantum emitters, yet their precise microscopic origins and formation mechanisms have remained contentious. In this work, we present a systematic first-principles study to definitively identify the four symmetry-inequivalent oxygen-vacancy (OV) configurations and elucidate their formation kinetics. By combining hybrid functional calculations of zero-phonon lines, zero-field-splitting parameters, and hyperfine interactions, we establish a unified assignment that revises prior models. Specifically, we confirm the identity of the well-known PL6 center as OV(hh), reassign the PL5 center from OV(hk) to OV(kh), and map the remaining two OV configurations to recently discovered oxygen-related emitters. Furthermore, our kinetic analysis reveals that defect formation is governed by the capture of mobile silicon vacancies by static substitutional oxygen atoms. Crucially, we demonstrate that the formation of the OV(kk) configuration is significantly hindered by a high-barrier interlayer migration path inherent to the unique stacking sequence of $4H$-SiC. This kinetic bottleneck provides a natural explanation for the experimental scarcity of this specific configuration. Finally, we provide dynamic evidence linking the kinetically favorable OV(hk) configuration to the ubiquitous PL7 center and outline a thermal annealing strategy for the deterministic generation of the elusive OV species.

We prove formally that the momentum-mixing Hatsugai-Kohmoto model (MMHK) is the Hubbard model with a twist. With this result in tow, we rely on the proof of Watanabe's that two models which differ by a twist must have the same bulk physics. Consequently, we have proven that MMHK = Hubbard in the charge sector.

We address the physics of a regular arrangement of independent magnetic impurities embedded in a band of interacting electrons. We focus on the one-dimensional case that can be studied using bosonization and in which the electron bulk is described by a Luttinger liquid. The impurity spins interact with the electrons via magnetic exchange that introduces the possibility of Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) physics. We find that, for two special values of the interactions, the model can be refermionized as a noninteracting electron band hybridized with a regular array of resonant levels. These solvable limits provide access to impurity correlators that correspond to either extended algebraic order or local screening. A physical picture emerges of how the interelectron interactions can stabilize either Kondo or RKKY physics depending on the sign of the interaction.

Thermal transport across GaN/SiC interfaces is governed by phonon transmission. However, how distinct interfacial bonding configurations (IBCs) modify heat transport remains poorly quantified. Moreover, previous molecular simulations have been hindered by the limited accuracy of empirical interatomic potentials. In this work, a machine-learned neuroevolution potential is constructed to overcome these limitations. Based on this potential, we reveal that distinct IBCs decisively govern interfacial thermal conductance (ITC). Specifically, the ITC of the N-Si bonded interface is 237% higher than that of the Ga-Si bonded interface, with other IBCs yielding intermediate values. The enhanced ITC of the N-Si interface is attributed to a lower interfacial energy barrier, longer lifetime of low-frequency phonons, strong phonon spectral overlap, and the emergence of extended interfacial vibrational modes, all of which facilitate phonon transmission across the interface. In contrast, Ga-Si interfaces exhibit strongly localized vibrational modes arising from high-frequency phonon annihilation and phonon spectrum mismatch, leading to significantly reduced ITC. Furthermore, the introduction of interfacial phonon bridges (AlN) can increase ITC by 46–237% by mediating phonon coupling across mismatched vibrational spectra. However, this bridging effect is weak for N-Si interfaces where phonon matching is already favorable; notably, the ITC of the N-C IBC exceeds that of the N-Si case at small AlN thicknesses. The present results demonstrate that atomic-scale bonding configurations and phonon-bridge structures provide an effective route to modulate interfacial heat transport, offering microscopic insight into phonon-mediated thermal transmission in GaN/SiC heterostructures.

Quantum-dot systems serve as nanoscale heat engines exploiting thermal fluctuations to perform a useful task. Here we investigate a multiterminal triple-dot system, operating as a refrigerator that extracts heat from a cold electronic contact. In contrast to standard heat engines, this system exploits a nonthermal resource. This has the intriguing consequence that cooling can occur without extracting energy from the resource on average—a seemingly demonic action—while, however, requiring the resource to fluctuate. Using full counting statistics and stochastic trajectories, we analyze the performance of the device in terms of the cooling-power precision, employing performance quantifiers motivated by the thermodynamic and kinetic uncertainty relations. We focus on two regimes with large output power, which are based on two operational principles: exploiting information on one hand and the nonthermal properties of the resource on the other. We show that these regimes significantly differ in precision. In particular, the regime exploiting the nonthermal properties of the resource can have cooling-power fluctuations that are suppressed with respect to the input fluctuations by an order of magnitude. We also substantiate the interpretation of the two different working principles by analyzing cross-correlations between input and output heat currents and information flow.

Quantized Thouless pumps in periodic systems, set by Chern numbers or Wannier-center winding, are by now fairly well established, whereas their quasiperiodic extensions still require further clarification. Here, we develop a general quantitative paradigm for bulk Thouless pumps in continuous models with spacetime quasiperiodicity, applicable to arbitrary spatial dimensions. Within this framework, the bulk pumping turns out to be governed by an emergent long-wavelength effective potential. Based on this mechanism, we obtain our main result, a universal relation between topological drift and the geometry of the quasi-Brillouin zone. Reduced to periodic systems, our result gives an explicit and compact formula, which enables us to directly calculate Chern numbers by microscopic data. These proposals are corroborated by simulations of one- and two-dimensional continuous moiré-type spacetime quasiperiodic lattices, which exhibit stable, localized, directional drift in excellent agreement with the theory.

We investigate the quantum dynamics of a one-dimensional spin-1/2 XX chain with anisotropic four-spin interactions (AFSI), focusing on its response to sudden quenches and its performance as a quantum battery. In the first part of our study, we analyze dynamical quantum phase transitions (DQPTs) resulting from quenches across different regions of the ground-state phase diagram. DQPTs emerge when the quench connects phases with different winding numbers. Crucially, we prove analytically that the dynamical topological order parameter remains identically zero for all quenches, including those across topological phase boundaries. This symmetry-induced cancellation reveals a fundamental decoupling between equilibrium topology and dynamical topological characterization. In the second part, we propose a quantum battery protocol driven by anisotropy quenches and investigate its energy storage performance. We show that the effective stored energy is highly sensitive to the initial and final anisotropy parameters and is maximized when the final Hamiltonian lies on the critical line, ${\beta }_c=1$, where the interaction becomes isotropic. Crucially, we uncover a direct link between nonequilibrium dynamics and charging behavior: for quenches performed far from the critical lines, both the stored energy and the power exhibit pronounced enhancements at the critical times where DQPTs occur. This establishes DQPTs as reliable dynamical markers for optimal charging performance. Our results demonstrate the interplay among topology, criticality, and nonequilibrium quantum dynamics, revealing new pathways for designing high-performance quantum batteries based on interaction symmetry and dynamical critical phenomena.

Field-tunable reconstruction of crystalline electric field (CEF) doublets offers a promising avenue for inducing multipolar character, while its observation in real materials has been little explored so far. Here we establish the honeycomb rare-earth chalcohalide NdOF as such a platform. Raman spectroscopy identifies four CEF excitations at 1.7, 15.6, 19.2, and 80.9 meV, and a Zeeman–CEF analysis reproduces their nonlinear field splitting into seven branches. Magnetization and susceptibility over 0.1–9 T are well described by a CEF model for the total angular momentum $J=9/2$ manifold, confirming the robustness of the extracted CEF scheme. These results demonstrate a field-driven continuous evolution of the ground-state doublet from dipolar to dipolar-multipolar character, with pressure providing a complementary tuning knob, establishing NdOF as a model system for exploring the controlled induction of multipolar components in rare-earth magnets.

Mercury telluride (HgTe) colloidal Quantum Dots (QDs) combine the inverted bandgap of bulk HgTe with tunable optoelectronic properties, making them ideal for infrared optoelectronic applications. In this work, we study spherical QDs with diameters up to 22 nm to explore their evolution from a conventional positive-gap semiconductor phase to a negative-gap phase at ambient and low temperatures. This transition is characterized by the crossover between conduction and valence levels, as occurs in the topological transition within HgTe quantum wells. We use a semiempirical tight binding model along with advanced solvers to compute the energy levels, wave functions, and oscillator strengths as functions of size. Our analysis reveals the progressive emergence of edge states associated with band inversion, as had already been predicted in HgS QDs. By comparing with predictions for QDs of conventional semiconductors such as CdTe, we highlight many unusual behaviors, such as a strong variation of the $s/p$ components of the wave functions with size, the increase in spin-orbit splitting between quantum levels as QD size increases, or a strong influence of spin-orbit coupling on the spatial shape of QD orbitals. Furthermore, certain optical transitions that are forbidden by symmetry in CdTe QDs become allowed in HgTe QDs. We also simulate absorption spectra for neutral and doped QDs, showing a complex interplay between interband and intraband transitions across the infrared range, the energy order between these different transitions can be reversed depending on the QD size. These effects have a strong influence on radiative recombination rates and their variation with size and temperature. Our results predict that the optical properties of HgTe QDs, when approaching the inverted-gap transition, are of great interest for infrared optoelectronic devices.

It is well known that an interface created by two topologically distinct phononic space structures could host nontrivial edge states that are immune to defects. Here, we propose a new class of phononic time crystals presenting chiral symmetry, and demonstrate the temporal version of topological edge states that exhibit superior robust properties. Our proposed phononic time crystal is equivalent to a temporal version of the Su-Schrieffer-Heeger model, and the chiral symmetry of this type of phononic time crystals quantizes the winding number defined in the Bloch frequency band. Specifically, the random temporal disorders do not impact the eigenfrequencies of the chiral-symmetry-protected edge states, while instead enhancing the temporal localizations of acoustic waves. Our work paves the way towards topological temporal control of acoustic wave with unique robustness.

Hybrid plasmonic waveguides, non-Hermitian exceptional points (EPs), and anisotropic 2D materials have so far been exploited mostly in isolation, each providing only one of the following: deep-subwavelength confinement, enhanced sensitivity, or dispersion control. Hyperbolic plasmon polaritons in black phosphorus (BP) further promise field localization but, in practice, are highly lossy, yielding strongly damped, short-range modes that limit device-level utility. Here, we present a single, electrically reconfigurable platform that combines these capabilities while recovering long-range, strongly confined hyperbolic fields: BP ribbons embedded in a hybrid-plasmonic slot waveguide. Electrostatic gating of BP tunes its anisotropic permittivity and drives the structure through four operation regimes at a fixed wavelength and geometry: (i) a delocalized regime in which index mismatch expels the slot mode, (ii) an index-matched EP where hybrid-plasmonic and waveguide eigenmodes coalesce and maximize responsivity, (iii) an epsilon-near-zero regime with deep-subwavelength confinement in the BP ribbons, and (iv) a hyperbolic regime that supports edge-guided canalization of high-$k$ fields with extended propagation lengths. This bias-programmable architecture overcomes the usual “one-phenomenon-per-platform” constraint and enables compact, CMOS-compatible modulators, sensors, and switches that cointegrate EP-enhanced sensitivity, ENZ localization, and hyperbolic light–matter interactions.

We develop a theory for the second-order time-reversal-odd ($\mathcal{T}$-odd) angular-momentum current, incorporating both spin and orbital components. We reveal that besides spin and orbital Berry curvature dipoles, the $\mathcal{T}$-odd nonlinear angular-momentum current can originate from disorder-induced mechanisms including coordinate shift, side-jump spin and orbital currents, anomalous scattering amplitude, and skew scattering. A general scaling relation is derived to help distinguish some of these contributions in experiments. Model calculations demonstrate that the orbital component can be comparable to and much larger than the spin component. Our theory lays the groundwork for $\mathcal{T}$-odd nonlinear spin and orbital transport.

Within the framework of non-Hermitian photonics, we investigate the spectral and dynamical properties of finite-sized one- and two-dimensional non-Hermitian off-diagonal disordered optical lattices, where randomness is applied to the intersite couplings rather than to the on-site potential terms. We analyze the eigenvalue distributions and the localization properties of the corresponding eigenmodes, and directly compare them with those of their Hermitian counterparts. In one dimension, we show that near-band-center non-Hermitian eigenmodes develop a sublattice-selective odd-even intensity imbalance. Furthermore, we study transport under single-channel excitation and identify unconventional phenomena such as jumps between distant lattice regions in systems with a purely real spectrum, as well as complex-spectrum–induced Anderson jumps, reported here for the first time in two dimensions. Our results establish a reference framework for non-Hermitian off-diagonal disorder and open new directions for future studies of localization phenomena. The reported effects can be experimentally observed in readily available optical platforms, such as synthetic-dimension mesh lattices.