Recent studies show that isotope engineering can lead to orders-of-magnitude variations of thermal radiation between two parallel plates. Considering the complexities introduced by many-body interactions, here we explore how the isotope effect on radiative thermal transport varies upon transition from two-body to many-body systems. A variety of basic geometrical configurations consisting of plates and particles are considered. With cubic boron nitride as a representative material, we demonstrate that the isotope effect in many-body systems can reach beyond ${10}^4$, which exceeds the maximum value in the parallel-plate geometry by more than sixfold. In addition, we find that for objects of different geometries, the radiative heat flow between isotopically identical materials is not necessarily the largest. These observations are attributed to the distinct and isotope-dependent phonon polaritons of the particles and plates, together with the configurational resonances between multiple closely spaced objects. We also systematically analyze the influence of a few geometrical parameters including the particle-particle distance, particle-plate distance, and plate thickness, as well as some key material properties. Our findings highlight the richness of isotope physics and provide an avenue for controlling thermal transport in many-body systems.

Intrinsic magnetic topological insulators offers an ideal platform to explore exotic topological phenomena, such as axion electrodynamics, the quantum anomalous Hall (QAH) effect and Majorana edge modes. However, these emerging new physical effects have rarely been experimentally observed due to the limited choice of suitable materials. Here, we predict the van der Waals layered ${\mathrm{V}}_2{\mathrm{WS}}_4$ and its related materials show intralayer ferromagnetic and interlayer antiferromagnetic exchange interactions. We find extremely rich magnetic topological states in ${\mathrm{V}}_2{\mathrm{WS}}_4$, including an antiferromagnetic topological insulator, the axion state with the long-sought quantized topological magnetoelectric effect, a three-dimensional QAH state, as well as a collection of QAH insulators and intrinsic axion insulators in odd- and even-layer films, respectively. Remarkably, the Néel temperature of ${\mathrm{V}}_2{\mathrm{WS}}_4$ is predicted to be much higher than that of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$. These interesting predictions, if realized experimentally, could greatly promote the topological quantum physics research and application.

Distinct from the $\text{SU}\left(2\right)$ case, the fermionic systems with $\text{SU}\left(N\right)$ symmetry are expected to exhibit novel physics, such as exotic singlet formation. Using the density matrix renormalization group technique, we obtain the ground-state phase diagram of the $\text{SU}\left(3\right)$ $t\text{−}J$ chain for density $n<1$. The ground-state phase diagram includes the Luttinger liquid, the extended Luther-Emery liquid characterized by a spin gap, and the phase separation state. We quantitatively assess the characteristics of the three phases by measuring spin gap, compressibility, various correlation functions, and structure factors. We further study the extended Luther-Emery liquid phase and discover molecular superfluid quasi-long-range order. The mechanism of the molecular superfluid is the combination of three $\text{SU}\left(3\right)$ fermions on sites that are not entirely connected. Accordingly, we can speculate the behavior of the $\text{SU}\left(N\right)$ $t\text{−}J$ chain model with larger $N$ values, operating within the same filling regime.

Over the past four decades, experimental studies of quantum phase transitions (QPTs) have been primarily focused on identifying these transitions in various materials and determining the critical exponents and universality classes associated with them. Since the critical exponents originate from the scale invariance, they are not explicitly tied to the microscopic physics of QPTs, which remains poorly understood for many systems. We have developed a model of QPTs, which addresses this deficiency. The model is based on the experimentally supported conjecture that the scaled data across a QPT depend, in a universal manner, on two system-specific length scales: the microscopic scale, $L_0$, typically known from general considerations (e.g., mean-free path, lattice constant) and the dephasing length, $L_{\phi }\left(T\right)$. Using this model, we have found that experimental data in the quantum critical regime of 18 distinct material classes can be quantitatively described by assuming that $L_{\phi }\left(T\right)$ is determined by the distance traveled by system-specific excitations during the Planckian time, ${\tau }_P=\hslash /k_{B}T$. In this work, we demonstrate how the model explains microscopic physics of QPTs in doped semiconductors and amorphous alloys, materials with Ising and Heisenberg spin chains, cold boson gases in optical traps, and the Mott transitions in organic semiconductors. The dynamics of excitations is determined by parameters such as the effective mass and diffusion coefficient, $D$, of the corresponding noninteracting or weakly renormalized system. For doped semiconductors and amorphous alloys, the noncritical behavior of $D$ in the quantum critical regime sharply contrasts with zero-temperature diffusion coefficient, which goes to zero at the transition. We also analyze the results of numerical studies of the Mott transition with dynamical mean-field theory, interpreting them as if they were experimental data. For these results, we find that, as expected, the microscopic scale matches the dimensionless lattice constant, $L_0\sim 1$. Finally, we report that the metal-insulator transition in Si:P, Ge:Sb, and Ge:As can be explained using a noninteracting version of the model.

We introduce a many-body state termed superpolarized electron-hole liquid to explain the multiferroic properties observed in a recent experiment on rhombohedral pentalayer graphene by Han et al. [Nature (London) 623, 41 (2023)]. Superpolarization refers to a state where electrons and holes are fully polarized in opposite directions within the extended spin-valley space, resulting in a polarization per charge that exceeds the saturated value of one. This state is characterized by triferroic order, exhibiting spontaneous polarization in spin, layer, and valley degrees of freedom. Specifically, layer polarization creates spontaneous electric dipole moments oriented perpendicular to the two-dimensional material stack, while valley polarization represents of momentum space condensation. The presence of this triferroic order allows a time-reversal even electric displacement field to induce a time-reversal breaking response, manifesting as the anomalous Hall effect. We also detail how valley polarization and orbital magnetization can be independently controlled through the experimental parameter space of electric displacement and magnetic fields. The concept of superpolarization can be probed experimentally through magnetic oscillation and local current distribution measurements to determine the area of the Fermi surfaces and their magnetic moments.

This Letter addresses the problem of constructing a proper bosonized description of the collective modes in strongly interacting (non-)Fermi liquids which is specific to two spatial dimensions. Although, in a mild form, this subtlety exists in the Fermi liquid as well, the discussion focuses on the effects of long-ranged and/or retarded interactions which can completely destroy the fermionic quasiparticles. The present analysis provides a further insight into the nature and properties of the collective bosonic modes in such systems.

The quest for room-temperature nanoscale magnets remains a central challenge, driven by their promising applications in quantum technologies. Layered $4d$ and $5d$ transition metal oxides with high magnetic ordering temperatures offer significant potential in this context. We explore ultrathin ${\mathrm{SrRu}}_2{\mathrm{O}}_6$ nanosheets using first-principles calculations, complemented by classical Heisenberg Monte Carlo simulations. Remarkably, these nanosheets exhibit robust antiferromagnetic ordering with Néel temperatures exceeding 430 K, despite the enhanced spin fluctuations characteristic of two-dimensional systems. Surface-termination-induced intrinsic charge doping introduces complexity to the magnetism, resulting in an insulator-to-metal transition and renormalized Néel temperatures in doped systems. A detailed microscopic analysis reveals distinct mechanisms underlying the magnetic behavior in electron- and hole-doped nanosheets. These findings provide a foundation for advancing theoretical and experimental studies in the largely unexplored realm of correlated oxides at the two-dimensional limit.

Exploiting the spin of waves is of fundamental interest for wave physics, with pivotal significance for diverse applications ranging from topological matters to information devices. However, only until recently has the spin of acoustic waves been unveiled. Here we theoretically reveal the spin in acoustics from the perspective of the Dirac-like equation. By introducing a four-component wave function that contains both pressure and velocity fields, the analogy between the coupled acoustic equations and the massless Dirac equation is established. Based on this, we find that the orbital angular momentum operator does not commute with the acoustic Dirac-like Hamiltonian, necessitating an additional spin operator to satisfy the angular momentum conservation, which naturally elucidates the origin of acoustic spin. The expression of the spin operator indicates that the scalar pressure field is spin 0 and the vector velocity field is spin 1. We also demonstrate that different types of dynamical properties, such as the canonical-Minkowski and the kinetic-Abraham types, can be unified in our theory framework by applying a weighting factor to the different components of the wave function. Furthermore, we present the invariance of the expectation values of dynamical operators during wave propagation, which corresponds to the conservation of dynamical properties with rational energy normalization. Our method offers insights into acoustics beyond traditional single-variable wave equations.

In this work, we have examined centrosymmetric polycrystalline ${\mathrm{GdRu}}_2{\mathrm{Si}}_2$ for topologically protected nontrivial chiral spin texture behavior using a variety of characterization techniques. Several studies have been carried out in the region surrounding the spin reorientation transition temperature (anticipated skyrmions phase) and the antiferromagnetic transition temperature ($T_N$ = 47 K). Below $T_N$, there are multiple metamagnetic transitions which lead to complicated magnetotransport behavior. The magnetic phase diagram has been constructed with the help of dc and ac magnetic susceptibility as well as dc resistivity. The topological Hall effect (THE) is also observed and displays complex behavior with sign changes above 20 K. In addition to the known skyrmionic phase regime, a new topological spin pattern, tentatively assigned to a multiple Q-spin structure, at higher temperatures (adjacent to the already reported skyrmion lattice phase) has been identified. Interestingly, Shubnikov–de Haas (S-dH) like quantum oscillations have also been seen in the magnetoresistance studies. Changes in quantum oscillation frequency and the deviation of oscillation amplitude from the Lifshitz-Kosevich fitting across distinct Q-spin textured regions point to the rebuilding of the Fermi surface as a result of interaction between localized spins of Gd and the conduction electrons. Also, angular magnetoresistance (AMR) results indicate the complex Fermi surface. Furthermore, above $T_N$, dc and ac magnetic susceptibility measurements mark the beginning of the Griffiths phase. Finally, a variety of topological spin states observed in a polycrystalline sample like this offers a straightforward approach to directly controlling the topology of spin textures. We feel that, for future applications, this study is a major step in understanding the mechanism of skyrmion stabilization in polycrystalline as well as centrosymmetric materials.

We propose a systematic wave-function-based approach to construct topological invariants for families of lattice systems that are short-range entangled using local parameter spaces. This construction is particularly suitable when given a family of tensor networks that can be viewed as the ground states of $d$-dimensional lattice systems, for which we construct the closed $(d+2)$-form higher Berry curvature, which is a generalization of the well-known 2-form Berry curvature. Such $(d+2)$-form higher Berry curvature characterizes a flow of $(d+1)$-form higher Berry curvature in the system. Our construction is equally suitable for constructing other higher pumps, such as the (higher) Thouless pump in the presence of a global onsite $\mathrm{U}\left(1\right)$ symmetry, which corresponds to a closed $d$-form. The cohomology classes of such higher differential forms are topological invariants and are expected to be quantized for short-range entangled states. We illustrate our construction with exactly solvable lattice models that are in nontrivial higher Berry classes in $d=2$.

Two-dimensional antiferromagnets are promising materials for spintronics. The van der Waals antiferromagnet ${\mathrm{NiPS}}_3$ has attracted extensive interest due to its ultranarrow exciton feature which is closely linked with the magnetic ordering. Here, we use time-resolved terahertz spectroscopy to investigate photoexcited carriers in ${\mathrm{NiPS}}_3$. We identify the onset of interband transitions and estimate the exciton dissociation energy from the excitation wavelength and fluence dependence of the transient spectral weight. Our results provide key insights to quantify the exciton characteristics and validate the band structure for ${\mathrm{NiPS}}_3$.

The effect of polaron formation on the ground state of excitons, trions, and biexcitons confined in ${\mathrm{CsPbBr}}_3$ nanocrystals is studied in the framework of effective mass Hamiltonians, using a Haken-like (Bajaj) potential for carrier-phonon coupling. The binding energy of trions agrees well with that observed in experiments, with position-dependent dielectric screening playing a significant role. For biexcitons, however, neither polaronic effects, nor dielectric confinement, nor electronic correlations—here accounted for with a variational quantum Monte Carlo method—suffice to explain the large binding energies reported by single nanocrystal spectroscopy experiments. This result reinforces the hypothesis that biexcitons polarize the perovskite lattice differently from excitons and trions.

Quantum phase transitions in Kondo-lattice compounds generally arise from the competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida exchange interaction. Magnetic field is a convenient control parameter of the competition and can smoothly suppress the magnetic ordering to zero temperature at a quantum critical point (QCP), where singular electronic properties beyond Fermi liquid often emerge, reflecting the enhanced quantum critical fluctuations. Here, we provide experimental evidence that the antiferromagnetic compound ${\mathrm{YbNi}}_4\mathrm{Cd}$, characterized by a weak Kondo coupling, can be tuned to QCP by applying a small field of less than 1 T. This tuning results in, however, no typical non-Fermi liquid behavior. Strong damping of quantum critical fluctuations in Zeeman field, which is comparable to the Kondo effect in this compound, is evidenced by low-temperature magnetic, specific-heat, and magnetocaloric effect measurements. Our findings are discussed as generic quantum critical characteristics of weak-coupling Kondo lattices, where the Kondo temperature is comparable to or smaller than the magnetic ordering temperature.

Correlations between the energies of a system's spectrum are one of the defining features of quantum chaos. They can be probed using the spectral form factor (SFF). We investigate how each spectral distance contributes in building this two-point correlation function. Specifically, starting from the spectral distribution of $k\mathrm{th}$-neighbor-level spacing $\left(k\mathrm{nLS}\right)$, we provide analytical expressions for the $k\mathrm{th}$-neighbor spectral form factor $\left(k\mathrm{nSFF}\right)$. We do so for the three Gaussian random matrix ensembles and the “Poisson” ensemble of uncorrelated energy levels. We study the properties of the $k\mathrm{nSFF}$, namely its minimum value and the time at which this minimum is reached, as well as the energy spacing with the deepest $k\mathrm{nSFF}$. This allows us to quantify the contribution of each individual $k\mathrm{nLS}$ to the SFF ramp, which is a characteristic feature of quantum chaos. In particular, we show how the onset of the ramp, characterized either by the dip or the Thouless time, shifts to shorter times as contributions from longer-range spectral distance are included. Interestingly, the even and odd neighbors contribute quite distinctively, the first being the most important to built the ramp. They respectively yield a resonance or antiresonance in the ramp. All of our analytical results are tested against numerical realizations of random matrices. We complete our analysis and show how the introduced tools help characterize the spectral properties of a physical many-body system by looking at the interacting XXZ Heisenberg model with local on-site disorder that allows transitioning between the chaotic and integrable regimes.

We study the influence of external electric and Zeeman fields on the Josephson effect in a planar superconductor/altermagnet/superconductor junction. Remarkably, we find that the current-phase relation (CPR) can be forward or backward skewed due to a pronounced second harmonic term. It decisively depends on the altermagnetic field strength. This second harmonic can be measured directly using double SQUID devices. The CPR skewness can be effectively manipulated by electric gating. Moreover, we identify two additional impacts of external electric and magnetic fields on the Josephson current: (i) Fields can induce 0-$\pi$ transitions. (ii) Fields can substantially enhance the critical current. This enhancement is surprising since supercurrents are typically suppressed by magnetic fields.

It has recently been established that open quantum systems may exhibit a strong spectral sensitivity to boundary conditions, known as the non-Hermitian/Liouvillian skin effect (NHSE/LSE), making the topological properties of the system boundary-condition sensitive. In this Letter, we ask the query: Can topological phase transitions of open quantum systems, captured by open boundary conditioned invariants, be observed in the dynamics of a system under periodic boundary conditions, even in the presence of NHSE/LSE? We affirmatively respond to this question, by considering the quench dynamics of entanglement spectrum in a periodic open quantum fermionic system. We demonstrate that the entanglement spectrum exhibits zero-crossings only when this periodic system is quenched from a topologically trivial to nontrivial phase, defined from the spectrum under open boundary conditions, even in systems featuring LSE. Our results reveal that non-Hermitian topological phases leave a distinctive imprint on the unconditional dynamics within a subsystem of fermionic systems.