Interacting or nonlinear lattices can host emergent particlelike modes, such as Bogoliubov quasiparticles, whose band topology and other properties are potentially highly tunable. Despite originating in the study of superconducting materials, Bogoliubov quasiparticles can also occur in synthetic metamaterials. Here, we implement a nonlinear driven-dissipative circuit whose fluctuations are Bogoliubov modes possessing nontrivial non-Hermitian band topology. We show experimentally that the system exhibits a switchable non-Hermitian skin effect (NHSE), which abruptly appears when the on-site driving voltage amplitude exceeds a threshold. In contrast to earlier realizations of the NHSE and related phenomena in circuit models, the switchable NHSE in our system occurs in Bogoliubov modes, which are strongly affected by how the system is driven. Moreover, unlike other experimental platforms hosting non-Hermitian Bogoliubov modes, our system does not rely on $p$-wave-like pairing interactions, only local nonlinearities.

The magnetotransport properties of a two-dimensional electron liquid in graphene are analyzed in the hydrodynamic limit under isothermal conditions. It is shown that the Wiedemann-Franz law does not hold in this regime and that the Lorenz ratios constructed from the diagonal and Hall conductivities generally differ from each other. The breakdown of the Wiedemann-Franz law is most pronounced near charge neutrality, where the Lorenz ratio can exceed its nominal universal Sommerfeld value by an order of magnitude. The corresponding Lorenz ratios exhibit a nonmonotonic dependence on the magnetic field, which is caused by emergent magnetic friction arising in liquids lacking Galilean invariance and possessing finite intrinsic conductivity.

We propose a Floquet time crystal model that responds in arbitrary multiples of the driving period. Such an $n$-tuple discrete time crystal is theoretically constructed by permutations in a disordered spin chain and is well suited for experimental implementations. Transitions between these time crystals with different periods give rise to a novel phase of matter that we call subspace-thermal discrete time crystals, where states within subspaces of definite charges are fully thermalized at an early time. However, the whole system still robustly responds to the periodic driving subharmonically, with a period being the greatest common divisor of the original two periods. Existing theoretical analysis from many-body localization cannot be used to understand the rigidity of such subspace-thermal time crystal phases. To resolve this, we develop a theoretical framework for the robustness of DTCs from the perspective of the robust $2\pi /n$ quasi-energy gap. Its robustness is rigorously proved if the system satisfies a certain condition where the mixing length, defined by the Hamming distance of the symmetry charges, does not exceed a global threshold. Although whether the condition is satisfied in generic disordered systems is unclear, the rigorous proof for DTC properties applies beyond the models considered here and extends to other existing DTCs realized by kicking disordered MBL systems, where the condition is automatically satisfied and conventional MBL-DTCs can be regarded as a special case of the subspace-thermal DTC with the subspace dimension being one, thus offering a systematic way to construct discrete time crystal models. We also introduce the notion of DTC charges that allow us to probe observables that spontaneously break the time-translation symmetry in both regular discrete time crystals and subspace-thermal discrete time crystals. Moreover, our discrete time crystal models can be generalized to systems with higher spin magnitudes or qudits, as well as to higher spatial dimensions.

Low-dimensional magnets are known for their intriguing magnetic properties, often intricately linked with a variety of other physical phenomena. In this study, we report that the spin-chain compound ${\mathrm{MnSb}}_2{\mathrm{O}}_4$ undergoes long-range antiferromagnetic (AFM) ordering at $T_N=52$ K. Analysis of neutron powder diffraction data reveals $A$-type AFM ordering with a magnetic space group of $C{c}^{\prime }cm$, associated with the magnetic point group $m^{\prime }\mathit{mm}$. The proposed magnetic structure is supported by first-principles density functional theory calculations, allowing a quantitative analysis of interatomic magnetic exchange interactions and providing crucial insights into the strength and nature of magnetic couplings. Interestingly, below $T_N$, a magnetic field-driven electric polarization with strong linear magnetoelectric coupling is observed, which is well supported by the magnetoelectric tensor associated with the m′mm symmetry. High-resolution synchrotron x-ray diffraction and Raman spectroscopy studies reveal a local structural distortion occurring below 150 K, which appears to be linked to the short-range AFM spin correlations prevailing well above $T_N$. Additionally, a significant phonon renormalization induced by spin ordering is observed, indicating substantial spin-phonon coupling in this system.

We analytically evaluate the currents in a planar-holed ideal (perfect magnetic shielding) superconductor when an axial dipole is located along the system's axis, obtaining a simple relation between the fluxoid (in this geometry, it equals the flux) threading the hole, the net current circling it, and the magnitude and position of the dipole. This expression has to be added to the basic screening equations describing the superconductor to understand the different physical situations that can appear. Thus several scenarios are studied: field and zero-field cooling cases, where the flux threading the hole is fixed; superconductors with a slit where the net current circling the hole is zero; and self-inductance case, where the flux threading the hole is only due to the screening currents. All the presented results are analytical for the axial dipole and are given as a function of the distance of the dipole from the plane of the superconductor. The obtained results can serve as a benchmark for recent and ongoing micromechanical experiments aimed at developing ultrasensitive gravimeters or applications searching for exotic spin-dependent interactions and dark matter, for example.

Describing electron-phonon interactions in a solid requires knowledge of the electron-phonon matrix elements in the Hamiltonian. State-of-the-art first-principles calculations for the electron-phonon interaction are limited to the one-electron-one-phonon matrix element, which is suitable for harmonic materials. However, there is no first-principles theory for one-electron-two-phonon interactions, which occur in anharmonic materials with significant electron-phonon interaction such as halide perovskites and quantum paraelectrics. Here we derive an analytical expression for the long-range part of the one-electron-two-phonon matrix element, written in terms of microscopic quantities that can be calculated from first principles. We show that the long-range one-electron-two-phonon interaction is described by the derivative of the phonon dynamical matrix with respect to an external electric field. We calculate the quasiparticle energy of a large polaron including one-electron-two-phonon interaction and show that it can be written in terms of a one-electron-two-phonon spectral function ${\mathcal{T}}_{\alpha \beta }\left(\omega \right)$. We demonstrate how to calculate this spectral function and its temperature dependence for the benchmark materials LiF and ${\mathrm{KTaO}}_3$, where it turns out that the effect is very small. The first-principles framework developed in this article is general, paving the way for future calculations of one-electron-two-phonon interactions in materials where the effect may be larger.

We report the design, synthesis, crystal structure, and physical properties of the layered intergrowth compound ${\mathrm{Eu}}_2{\mathrm{CuMn}}_2{\mathrm{P}}_3$. The structure of ${\mathrm{Eu}}_2{\mathrm{CuMn}}_2{\mathrm{P}}_3$ features an alternating arrangement of hexagonal EuCuP block layers and trigonal ${\mathrm{EuMn}}_2{\mathrm{P}}_2$ block layers, interconnected through shared Eu planes. This structural hybridization leads to multiple magnetic orderings in ${\mathrm{Eu}}_2{\mathrm{CuMn}}_2{\mathrm{P}}_3$: weak antiferromagnetic (AFM) ordering of Mn at $T_{\mathrm{N}}^{\mathrm{Mn}}$ = 80 K, AFM ordering of Eu at $T_{\mathrm{N}}^{\mathrm{Eu}}$ = 29 K, a spin-reorientation transition at $T_{\mathrm{SR}}$ = 14.5 K, and weak ferromagnetism below $T_{\mathrm{N}}^{\mathrm{Mn}}$. The spin configurations in different temperature regions are discussed based on the calculations of magnetic energies for various collinear arrangements. Resistivity measurements reveal a pronounced transition peak at $T_{\mathrm{N}}^{\mathrm{Eu}}$, which is suppressed in the presence of a magnetic field, resulting in a significant negative magnetoresistance effect. The computed semimetallic band structure, characterized by a small density of states at the Fermi level, aligns well with experimental observations. The successful synthesis of ${\mathrm{Eu}}_2{\mathrm{CuMn}}_2{\mathrm{P}}_3$ and its fascinating magnetic properties highlight the effectiveness of our block-layer design strategy. By assembling magnetic block layers of compounds with compatible crystal symmetries and closely matched lattice parameters, this approach opens exciting avenues for discovering layered materials with unique magnetic behaviors.

We investigated temperature-driven spin reorientation (SR) in the itinerant kagome magnet ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$ using high-resolution synchrotron x-ray diffraction, neutron diffraction, magnetometry, and magnetic force microscopy (MFM), further supported by phenomenological analysis. Our study reveals a crossover from the state with easy-plane anisotropy to the high-temperature state with uniaxial easy-axis anisotropy taking place between $\sim 40$ and 130 K through an intermediate easy-cone (or tilted spin) state. This state, induced by the interplay between the anisotropy constants $K_1$ and $K_2$, is clearly manifested in the thermal evolution of the magnetic structure factor, which reveals a gradual change of the SR angle $\theta$ between 40 and 130 K. We also found that the SR is accompanied by a magnetoelastic effect. Zero-field MFM images across the SR range show a transformation in surface magnetic patterns from a dendritic structure at 120 K to domain-wall-dominated MFM contrast at 40 K. Our analysis suggests that the SR and associated microstructural transformations are the results of competing first- and second-order anisotropy constants.

Bright sources of quantum microwave light are an important building block for various quantum technological applications. Josephson junctions coupled to microwave cavities are a particularly versatile and simple source for microwaves with quantum characteristics, such as different types of squeezing. Due to the inherent nonlinearity of the system, a pure dc-voltage bias can lead to the emission of correlated pairs of photons into a stripline resonator. However, a drawback of this method is that it suffers from bias voltage noise, which disturbs the phase of the junction and consequently destroys the coherence of the photons, severely limiting its applications. Here we describe how adding a small ac reference signal either to the dc bias or directly into the cavity can stabilize the system and counteract the sensitivity to noise. We first consider the injection locking of a single-mode device before turning to the more technologically relevant locking of two-mode squeezed states, where phase locking preserves the entanglement between photons. Finally, we describe locking by directly injecting a microwave into the cavity, which breaks the symmetry of the squeezing ellipse. In all cases, locking can mitigate the effects of voltage noise and enable the use of squeezed states in quantum technological applications.

In recent years, pure crossed Andreev reflection has attracted much attention due to its scientific significance and potential applications. Here, we investigate the crossed Andreev reflection in a monolayer $1{\mathrm{T}}^{\prime }-{\mathrm{MoS}}_2$-based normal metal-superconductor-normal metal junction by solving the Dirac-Bogoliubov-de Gennes equation. It is found that an electric field can be used to modulate the pure crossed Andreev reflection without the local Andreev reflection and the elastic cotunneling when the signs of Fermi energies in two normal regions are opposite. The maximum pure crossed Andreev reflection conductance increases as the incident energy rises. Interestingly, the distribution of transmitted angle of hole exhibits spin-valley locking and direction separation, resulting from the tilted and anisotropic band structure, which resembles the Hall effect and is referred to as the nonlocal tunneling spin-valley locking Hall effect. Furthermore, the nonlocal tunneling spin-valley locking Hall conductance and the corresponding Hall angle are calculated as functions of the junction length and electric field. A giant spin-valley locking Hall angle, ranging from approximately 2 to 45, is found by selecting appropriate physical parameters in the absence of Berry curvature. Our findings can be utilized to manipulate the spin-valley locking entangled state, especially involving in the Cooper pair splitter, and more generally, offering potential applications in both spintronics and valleytronics.

We demonstrate the existence of a maximum for the enhancement of the far-field heat transfer between deep-subwavelength membranes of SiC. Using fluctuational electrodynamics, we show that the thermal conductance reaches a peak exceeding the blackbody limit by 460 times for 50-nm-thick membranes of SiC at 200 K. This enhancement is driven by the interplay of two surface polariton modes, whose combined contributions are optimized at this thickness and temperature. Our finding thus reveals that the tradeoff of two polariton resonances limits the ability of subwavelength polar membranes to enhance thermal radiation.

In this work we analyze a class of moiré models consisting of an active honeycomb monolayer such as graphene or a hexagonal transition-metal dichalcogenide on top of a substrate, in which the K and ${\mathrm{K}}^{\prime }$ valleys of the active layer are folded near each other by a suitably chosen substrate geometry. Generalizing the so-called “coupled-valley” model of M. G. Scheer and B. Lian [Phys. Rev. B 108, 245136 (2023)], we start from a microscopic tight-binding description, deriving a continuum model from Schrieffer–Wolff perturbation theory and obtaining an effective description of the low-energy momentum states in either valley as well as the explicit microscopic forms of the moiré potentials. We then consider two explicit symmetry-mismatched moiré geometries with a rectangular substrate, the first of which displays an emergent time-reversal symmetry as well as a broad parameter regime which displays quasi-1D physics characterized by the existence of a sliding Luttinger liquid phase. This model also has a nontrivial topological character, captured by the Berry curvature dipole. The second geometry displays an emergent $C_3$ rotational symmetry despite the rectangular substrate, reducing to a continuum model considered by Scheer and Lian that was shown to display honeycomb and kagome topological flat bands.

Octahedral antiferromagnets are distinguished by crystal lattices composed of octahedra of magnetic ions. In the fully frustrated case, the Heisenberg Hamiltonian can be represented as a sum of squares of total spins for each octahedral block. We study the fully frustrated spin model for a lattice of edge-shared octahedra, which corresponds to the $J_1–J_2$ fcc antiferromagnet with $J_2/J_1=1/2$. The magnetization process at this strongly frustrated point features a remarkably rich sequence of different magnetic phases that include fractional plateaus at $m=1/3$ and $2/3$ values of the total magnetization. By performing extensive Monte Carlo simulations, we construct the $H–T$ phase diagram of the classical model with eight field-induced states, which acquire stability via the order by disorder mechanism. These antiferromagnetic states have distinct spin configurations of their octahedral blocks. The same spin configurations are also relevant for the fully frustrated corner-shared model, bringing an apparent similarity to their field-induced states.

We study the effects of superconducting $p$-wave pairing on the non-Hermitian Aubry-André-Harper model with power-law hopping. For the case of short-range hopping, weak pairing leads to oscillating quasi-Majorana zero modes, turning to edge-localized Majorana zero modes as pairing strength increases. For the case of long-range hopping, we observe the emergence of massive Dirac modes having oscillatory behavior, similar to Majorana modes with weak pairing. The massive Dirac modes localize at the edges as the pairing strength grows. The superconducting pairing spoils the plateaus observed in the fractal dimension of all the energy eigenstates of the Aubry-André-Harper model with power-law hopping. The number of plateaus decreases with the increasing pairing strength for the weak non-Hermiticity in the system. The phase diagram of the system reveals that real and complex energy spectra correlate differently with the localization properties of the eigenstates, depending on the strength of pairing and hopping range.

Dynamical quantum phase transitions (DQPTs) probe the nonequilibrium evolution of quantum systems, unveiling their geometric and topological characteristics. In this study, we introduce the concepts of parallel quench and dynamic geometrical order parameter (DGOP) for nonband models without momentum-space structure, where these quantities capture the geometric shifts associated with DQPTs. At zero temperature, the DGOP corresponds to the Pancharatnam geometric phase, while at finite temperatures, it extends to the interferometric geometric phase. We further generalize the dynamic topological order parameter (DTOP) to finite-temperature band models, examining its behavior in the Su-Schrieffer-Heeger model. Our analysis shows that thermal fluctuations and boundary effects at finite temperatures disrupt the quantization of the DTOP, yet it retains signatures of topological transitions. These findings deepen the understanding of geometric and topological properties in quantum dynamics, illuminating DQPTs across both nonband and band frameworks.

Altermagnetism has been proposed as a new type of magnetism, simultaneously exhibiting compensated spin moments in real space and spin-split electronic bands in reciprocal space. Alternating chiral magnon splitting is considered a unique feature of altermagnets. In this paper, utilizing linear spin-wave theory (LSWT), which is based on a localized spin picture and itinerant linear-response time-dependent density functional theory (LR-TDDFT), we investigate the spin fluctuation spectra of altermagnetic CrSb. Along the $L\text{−}\mathrm{\Gamma }\text{−}{L}^{\prime }$ path, the LSWT provides a chiral magnon splitting of up to 9 meV, located at high excitation energies around 140 meV, which is identified to be primarily driven by the splitting of two long-range exchange interactions, with exchange paths along the body diagonal lines of the unit cell. On the other hand, the more realistic LR-TDDFT obtains more significant splitting of $\sim 30\mathrm{meV}$ at maximum. However, the splitting is severely smeared out due to strong Landau damping from the Stoner continuum, which may make it difficult to observe experimentally, e.g., through inelastic neutron scattering. We further provide a brief discussion on the connection between the Stoner excitations and the chiral magnon splitting.

We investigate the ground-state magnetism of a Hubbard model in a system consisting of a main frame (subsystem) and a particle bath (center sites). The hole doping in the main frame is controlled by adjusting the chemical potential of the particle bath. In the weakly doped region, the saturated ferromagnetic state emerges due to the Nagaoka mechanism [Phys. Rev. B 90, 224426 (2014)]. However, in the highly doped region, a variety of intriguing magnetic states are observed, including partially polarized states and nonmagnetic states. To understand these states, we analyze the state of the subsystem by comparing its properties with those of a two-leg ladder system, which corresponds to the subsystem with the center sites removed. Furthermore, to gain insight into the microscopic origin of the magnetic phase diagram, we study the ground state of the corresponding effective $t\text{−}J$ model, derived from the Hubbard model by considering the second-order processes of the electron hopping. The phase diagram is well reproduced by the effective $t\text{−}J$ model, which includes the three-site pair-hopping term. To elucidate the competition among different energy contributions, such as potential, kinetic, and magnetic energies, we classify the energies within the effective $t\text{−}J$ model.

Taking the quantum Kitaev chain as an example, we have studied the universal dynamical behaviors resulting from quantum criticality under the condition of environmental temperature quench. Our findings reveal that when the quantum parameter is at its critical value, both the excess excitation density at the end of linear quench and the free relaxation exhibit universal scaling behaviors. The scaling laws observed upon quenching to the zero-temperature quantum critical point and nonzero temperature points exhibit distinct scaling exponents, which are all intimately related to the dynamical critical exponents of the quantum phase transition. Additionally, for the case of linear quench to finite temperatures, we have also discovered an intrinsic universal dynamical behavior that is independent of quantum criticality. Our research offers profound insights into the relationship between quantum criticality and nonequilibrium dynamics from two perspectives: Kibble-Zurek-like scaling behavior and free relaxation dynamics. Notably, the Kibble-Zurek-like scaling behavior in this context differs from the standard Kibble-Zurek mechanism. These two aspects jointly open up a new avenue for us to understand quantum criticality through real-time dynamical behavior, even at finite temperatures.