Parity-time symmetry constrains the spectrum of non-Hermitian systems to be either real or come in complex conjugate pairs. The transition between a symmetry-preserving phase with real energies and a symmetry-broken phase with complex energies is marked by exceptional points, one of the hallmarks of non-Hermitian systems. Because of these properties, these systems are widely studied, both theoretically and experimentally. In this work, we investigate the thermodynamic properties of the gain and loss Su-Schrieffer-Heeger model for both bosons and fermions, and establish the existence of an imaginary time crystal phase, an imaginary time analog of a time crystal. This phase occurs when there is a resonance condition between the Matsubara frequencies and the spectrum of the system, making the Green's function of the system oscillate in imaginary time with the Matsubara frequency. We show that this phase appears in the symmetry-broken region. In particular, the topological edge states of this system exhibit oscillations that are present for fermions. Finally, we discuss the applicability of our results for experiments. We examine signatures of these phases in terms of correlation functions in real time and oscillations in thermodynamic potential in inverse temperature $\beta$, and explore possible experimental platforms to realize this system.

The combination of Maxwell and Bloch equations is an ideal framework to describe ultrafast time-resolved x-ray experiments on an attosecond timescale in crystals. However, broadband experiments such as x-ray absorption near-edge spectroscopy or resonant inelastic x-ray scattering require detailed knowledge of the electronic structure and transition matrix elements. Here, we show how to fill this gap by combining the Maxwell-Bloch formalism with first-principles calculations treating explicitly the core states. The resulting x-ray absorption spectrum recovers key spectral signatures which were missing in previous work relying on a semiempirical tight-binding approach.

Nodal topological superconductivity (NTSC) with flat Majorana boundary modes connecting gapless nodal points represents a nontrivial superconductivity (SC) phase capable of fault-tolerant topological quantum computing. In addition to unconventional SC with nodal pairing gap, two-dimensional (2D) NTSC has been effectively achieved from conventional $s$-wave SC by applying a magnetic field to symmetry-protected out-of-plane persistent spin texture (PST). Here we demonstrate that the effective NTSC can be alternatively achieved from in-plane PST under the ferromagnetic proximity effect, where the gapless nodal points within the SC gap remain robust at the entire energy range of the PST-enforced nodal line electronic states. This discovery positions (110)-oriented GaAs/AlGaAs and InAlAs/InGaAs quantum wells with extrinsic in-plane PST as ready-made NTSC platforms. Meanwhile, we propose that intrinsic in-plane PST is available in 2D stoichiometric materials with $C_{2v}$ or $D_2$ point group symmetry by balancing different antisymmetric spin-orbit coupling effects. Our first-principles calculations indicate the balance is readily struck in monolayer $X\mathrm{ThB}{\mathrm{r}}_6$ ($X=\mathrm{Ca}$, Sr, Ba) with $C_{2v}$ symmetry, while $D_2$ symmetry enforced in-plane PST is identified in $\mathrm{Au}{\mathrm{O}}_2\mathrm{Br}$ and $\mathrm{Cu}{\mathrm{O}}_2\mathrm{F}$ monolayers. This work not only expands the theoretical framework of effective NTSC, enabling its implementation in experimentally prepared quantum wells, but it also introduces a feasible route to achieve intrinsic in-plane PST in 2D stoichiometric compounds for device miniaturization.

Achieving room-temperature strong light-matter coupling with scalable, high-performance platforms remains a critical challenge in quantum photonics. We present a hybrid perovskite metasurface architecture that effectively integrates Mie resonances, lattice surface plasmon polaritons (LSPPs), and excitons (X) within a Fabry-Pérot (FP) cavity to enhance light-matter interactions. The system employs phenethylammonium lead iodide metasurface disks embedded in a dielectric cavity, facilitating three-mode hybridization (Mie-LSPP-X) through cavity-mediated coupling. Theoretical analysis reveals that the FP cavity redistributes Mie-mode electric fields from the edges of disks to their interior, significantly enhancing photon-exciton spatial overlap compared to two-mode Mie-X metasurfaces. Through the analysis using the coupled oscillator model, this amplification yields a Rabi splitting of 231.6 meV, which is more than twice that of two-mode Mie-X systems. The design leverages perovskite advantages, including high exciton binding energy and solution processability, alongside the subwavelength confinement of Mie resonances and diffractive coupling of LSPPs, while minimizing plasmonic losses. The hybrid platform demonstrates potential for exploring quantum phenomena like polariton condensation and optical switching, while advancing practical applications such as low-threshold polariton lasers, all-optical logic devices, and sensors.

The green phase compounds $R_2\mathrm{BaCu}{\mathrm{O}}_5$ ($R=\mathrm{Rare}$ earth) have recently emerged as promising candidates for magnetoelectric coupling arising from $4f\text{−}3d$ exchange interactions. Here, we report the discovery of multiferroicity in a previously unexplored magnetic phase of $\mathrm{Y}{\mathrm{b}}_2\mathrm{BaCu}{\mathrm{O}}_5$. While earlier studies identified two antiferromagnetic (AFM) transitions below 15 K, our comprehensive investigation using magnetic, heat capacity, and neutron diffraction reveals three successive magnetic transitions occurring at $T_{\mathrm{N}1}=15.9$ K, $T_{\mathrm{N}2}=5.2$ K, and $T_{\mathrm{N}3}=3.5$ K. Neutron diffraction study evidences a sequence of magnetic phases: a transition from a paramagnetic state to (i) a first commensurate (CM) AFM phase with ${\mathbf{k}}_{\mathbf{1}}=\left(0,{}^1/{}_2,0\right)$, below $T_{\mathrm{N}1}$, (ii) an incommensurate (ICM) AFM phase with ${\mathbf{k}}_{\mathbf{2}}=(0,\delta ,0)$, below $T_{\mathrm{N}2}$, and (iii) a second commensurate AFM phase with ${\mathbf{k}}_{\mathbf{3}}=\left(0,{}^1/{}_2,{}^1/{}_2\right)$ below $T_{\mathrm{N}3}$. Notably, multiferroic behavior emerges exclusively in the incommensurate AFM region, consistent with the deduced polar magnetic symmetry $2mm$. These results establish $\mathrm{Y}{\mathrm{b}}_2\mathrm{BaCu}{\mathrm{O}}_5$ as a new spin-driven multiferroic and underscore the critical role of $4f\text{−}3d$ coupling in governing the magnetoelectric properties of the $R_2\mathrm{BaCu}{\mathrm{O}}_5$ family.

In this Letter we consider the time-dependent Kondo model where a magnetic impurity interacts with the electrons through a time-dependent interaction strength $J\left(t\right)$. We develop an alternative framework based on the Bethe ansatz and construct an exact solution to the time-dependent Schrödinger equation. We show that when periodic boundary conditions are applied, the consistency of the solution results in a constraint equation which relates the amplitudes corresponding to a certain ordering of the particles in the configuration space. This constraint equation takes the form of a matrix difference equation, and the associated consistency conditions restrict the interaction strength $J\left(t\right)$ for the system to be integrable. For a given $J\left(t\right)$ satisfying these constraints, the solution to the matrix difference equations provides the exact many-body wave function that satisfies the time-dependent Schrödinger equation. We provide a concrete example of $J\left(t\right)$ which satisfies these constraint equations. We show that in this case, the matrix difference equations turn into quantum Knizhnik-Zamolodchikov (qKZ) equations, which are well studied in the literature. The framework developed in this Letter allows one to probe the nonequilibrium physics of the Kondo model, and being general, it also allows one to solve a new class of Hamiltonians with time-dependent interaction strengths which are based on quantum Yang-Baxter algebra.

Cavity polaritons, hybrid half-light half-matter excitations in quantum microcavities in the strong-coupling regime, demonstrate clear signatures of quantum collective behavior, such as analogs of Bose-Einstein condensates and superfluidity at remarkably high temperatures. The analysis of the formation of these states demands an account of the relaxation processes in the system. Although there are well-established approaches for the description of some of them, such as finite lifetime polaritons, an external optical pump, and coupling with an incoherent excitonic reservoir, the treatment of pure energy relaxation in a polariton fluid still remains a puzzle. Here, based on the quantum hydrodynamics approach, we derive the corresponding equations where the energy relaxation term appears naturally. We analyze in detail how it affects the dynamics of polariton droplets and the dispersion of elementary excitations of a uniform polariton condensate. Although we focus on the case of cavity polaritons, our approach can be applied to other cases of bosonic condensates, where the processes of energy relaxation play an important role.

The Holstein model is a benchmark model of systems with electron-phonon interaction. However, its electrical transport properties are not yet fully understood. In this work, we performed numerically exact calculations of the imaginary-time current-current correlation function of the Holstein Hamiltonian for a broad range of model parameters. These calculations were performed using a path-integral-based quantum Monte Carlo method. We compared these results with the results obtained under the assumption of conventional band transport, small polaron hopping, and polaron band transport. From this comparison, we identified the regions in parameter space where each of these transport regimes is valid. In some cases when an imaginary-time comparison of current-current correlation functions could not give conclusive results, we complemented it with real-time comparisons or a comparison with the literature data on numerically exact dc mobilities. Overall, we found that the parameter space is almost completely covered by the three mentioned transport regimes.

Superconductivity in transition metal oxides (TMOs) usually favors oxygen-rich compositions, where polyhedral units surround transition metals, minimizing interaction between neighboring atoms. Herein we report a pressure-induced Pnma phase of $\mathrm{Nb}{\mathrm{O}}_2$, identified by first-principles swarm structure calculations, featuring one-dimensional linear Nb chain. The formation of this Nb chain is fundamentally attributed to the interaction of $4d_{x2-y2}$ electrons of adjacent Nb atoms, which contribute the metallic character of $\mathrm{Nb}{\mathrm{O}}_2$. Electron-phonon coupling calculations reveal strong interactions between Nb $4d_{x2-y2}$ states and low-frequency Nb-dominated phonon modes, playing a crucial role in driving the superconducting transition. Remarkably, $\mathrm{Nb}{\mathrm{O}}_2$ can be quenched to ambient pressure and exhibits a superconducting transition temperature ($T_c$) of 20 K, the highest-$T_{\mathrm{c}}$ value reported to date among binary TMOs.

By revisiting the fractional Fermi number through the perspective of spectral asymmetry, a unified approach to fractional Fermi numbers in the presence of topological point defects is established based on complex analysis. When applied to the generic Dirac system, our approach shows that the fractional Fermi number is ultimately expressed as a surface integral evaluated over a sphere surrounding the defect at spatial infinity. This result clearly demonstrates that fractional Fermi number is determined by the defect's global topology, rather than its local details. We further apply our approach to concrete Dirac systems in various dimensions. For the one-dimensional case, it directly reproduces the seminal Goldstone-Wilczek formula. As for the two-dimensional case, it yields a fractional Fermi number proportional to the topological charge of the defect ($N_0$), even when the chiral symmetry is broken by an additional mass term. If the chiral symmetry is restored as the mass approaches zero, the fractional Fermi number is quantized to $\pm N_0/2$ with the sign inherited from the mass even in this limit. Additionally, we provide a supersymmetric interpretation about the bound states. For the three-dimensional massive Dirac system, our method yields an elegant formula of fractional Fermi number proportional to the topological charge of the defect ($N_1$). If the chiral symmetry is restored, the fractional Fermi number is quantized to $\pm N_1/2$.

Hydrogen and helium constitute the main components of Jovian planets. Under the warm dense conditions inside gas giants, helium droplets settle deeper into the planet, forming a helium gradient. Consequently, thermodynamic properties, such as the equation of state (EoS) and sound speed, of hydrogen-helium mixtures with varying atomic helium mole fractions $\left(x_{\mathrm{He}}\right)$ under warm dense conditions are crucial for evaluating EoS models used in astrophysical modeling. To this end, we conducted multiple reverberation compression experiments on gaseous deuterium-helium $\left({\mathrm{D}}_2\text{−}\mathrm{He}\right)$ mixtures with two distinct $x_{\text{He}}$ of 0.14 and 0.60. The multishock pressures reached 110 GPa, and reshock temperatures reached 7620 K, conditions directly relevant to planetary interiors. The obtained EoS and sound velocity are used to evaluate ${\mathrm{H}}_2\text{−}\mathrm{He}$ EoS models constructed with or without taking into account nonideal mixing (NIM) effects. It is found that the state-of-the-art $\mathrm{CMS}19+\mathrm{HG}23$ EoS model, which incorporates NIM effects for arbitrary $x_{\text{He}}$ values, can reasonably reproduce the measured pressure-density EoS for both mixtures but underestimates the shock temperature of the $x_{\text{He}}=0.14$. First-principles molecular dynamics (FPMD) simulations reveal that the NIM effect, arising from the strengthening effect of helium on deuterium molecule bonds, is more prominent for the mixture with $x_{\text{He}}=0.60$. Our findings impose new constraints on the EoS models applicable to the mixtures with arbitrary $x_{\text{He}}$, which are crucial for modeling the structure and evolution of gas giants.

We describe the results of x-ray fluorescence holography (XFH) measurements of $1T^{\prime }\text{−}{\mathrm{TaTe}}_2$, in which Ta ribbon clusters that appear at high temperatures change to heptamers at low temperatures. It was previously thought that the ribbon cluster in the high-temperature phase was composed of multiple linear trimers formed by three-center two-electron $\sigma$ bonds, but recent structural studies have revealed that the Ta atoms at the trimer centers are slightly displaced in the direction of the chain extension. Since it is thought that this local displacement is ordered to form a low-temperature heptamer, elucidating the origin of the local displacement is an important issue. Our XFH measurements revealed that there is no attractive interaction between the Ta atoms that are locally displaced, but rather there is a repulsive interaction. This indicates that the origin of the heptamer formation is not due to cluster formation such as a charge density wave occurring in the direction of the chain extension. We discuss that the origin of the local atomic displacement is the formation of random dimers between different Ta sites.

This paper presents a Landau treatment of the incommensurate density wave transition observed in trilayer Ruddlesden-Popper nickelates and uses this to address the nature of the transition. The data are consistent with a spin driven transition with the distinct intertwining of charge and spin order due to being in or proximate to the first-order transition region of the Landau phase diagram. From this approach, one also obtains an understanding of the variation of the transition temperature with rare earth size, pressure, and oxygen isotope substitution.

We calculate the viscoelasticity tensor for altermagnets and formulate the corresponding hydrodynamic equations. The anisotropy of altermagnetic Fermi surfaces allows for additional terms in the viscoelasticity tensor and is manifested in transport properties, including electron and spin flows in a channel and nonlocal responses. In the channel geometry, the altermagnetic spin splitting leads to nontrivial spin density and spin current. Like the electric current, the spin current acquires a Poiseuille profile for no-slip boundary conditions. In nonlocal responses, the altermagnetic anisotropy affects current streamlines and electric potential distributions in the viscous regime. Our results provide signatures of the hydrodynamic transport regime in altermagnets, potentially facilitating its experimental studies and discovery.

Charge detection offers a powerful probe of mesoscopic structures based on quantum dots, but it also invariably results in measurement back-action (MBA). If strong, MBA can be detrimental to the physical properties being probed. In this work, we focus on the effects of MBA on an Anderson impurity model in which the impurity is coupled electrostatically to a detector. Introducing a nonperturbative method, we explore the interplay of coherent dynamics, strong correlations, and nonequilibrium conditions. The effects of MBA can be seen most clearly in the temperature derivative of the occupation. In the nonequilibrium case, we identify this as arising because of an energy flow from the detector to the impurity.

Magnetic order typically disrupts superconductivity, reducing the supercurrent. Here, we show that chiral antiferromagnetism, with nonrelativistic spin-split bands and distinctive valley-locked spin texture, can instead significantly enhance Josephson supercurrents. This enhancement stems from the emergence of dominant equal-spin triplet pairing and strong fluctuations of singlet pairing in momentum space, both induced by chiral antiferromagnetism. We demonstrate these results in Josephson junctions composed of chiral antiferromagnetic metals and conventional superconductors on kagome lattices. Furthermore, we show that the enhanced Josephson supercurrent is stabilized in a $\pi$-junction state. These phenomena persist across a broad energy range and remain stable for different temperatures and junction lengths. Our results unveil a previously unexplored mechanism for enhancing supercurrent by strong magnetic order and provide crucial insights into the large Josephson currents observed in ${\mathrm{Mn}}_3\mathrm{Ge}$.

The subject of this study is spin transport through a molecular orbital connected to two leads, and coupled via exchange interaction with a precessing anisotropic molecular spin in a constant magnetic field. The inelastic spin-flip processes between molecular quasienergy levels are driven by the molecular spin precession. By setting the Larmor frequency, the tilt angle of molecular magnetization with respect to the magnetic field, and the magnetic anisotropy parameter, one can modulate the spin current and noise, spin-transfer torque, and related torque coefficients. Moreover, the dc-spin current and spin-transfer torque components provide the quasienergy level structure in the orbital. Quantum interference effects between states connected with spin-flip processes manifest themselves as dips (minimums) and peaks (maximums) in spin-current noise, matching Fano-like resonance profiles with equal probabilities of interfering elastic and inelastic spin-flip pathways. By proper adjustment of the anisotropy parameter and magnetic field, the precession is suppressed and the torque vanishes, revealing the anisotropy parameter via a dc-spin current or torque measurement. The results of the study show that spin transport and spin-transfer torque can be manipulated by the anisotropy parameter even in the absence of the magnetic field.

A two-dimensional epsilon-mu-near-zero metamaterial constructed from a simple two-phase photonic crystal with a squared lattice is proposed and demonstrated in this work. The photonic crystal can generate two distinct Dirac-like points and achieve the epsilon-mu-near-zero response at two different frequencies for the transverse electric polarization mode and the transverse magnetic polarization mode. According to the band structure and the mode analysis, the triply accidental degeneracy of Dirac-like points is analyzed and the corresponding epsilon-mu-near-zero properties at the Dirac-like points are validated via the effective-medium theory. Finally, the full-wave simulations based on the finite-element method are conducted to prove the epsilon-mu-near-zero properties of the photonic crystal. The results demonstrate that the photonic crystal exhibits special epsilon-mu-near-zero properties such as nearly lossless electromagnetic transmission without phase variation and the electromagnetic cloaking at two distinct Dirac-like points.