Non-Hermiticity greatly expands existing physical laws beyond the Hermitian framework, revealing various phenomena with unique properties. To date, most exotic non-Hermitian effects, such as exceptional points and non-Hermitian skin effects, have been discovered in single-particle systems. The interplay between non-Hermitian and particle interactions is expected to be a more fascinating but much less explored area. Here, we report an experimental simulation of a strongly correlated non-Hermitian few-body system and reveal a type of non-Hermitian skin state toward effective boundaries in Hilbert space induced by strong interactions. Such an interaction-induced non-Hermitian effect represents the aggregation of bosonic clusters with nonidentical occupations in the periodic lattice, and we call it the non-Hermitian aggregation effect. By mapping the eigenstates of three correlated bosons to modes of the designed three-dimensional electric circuit, the interaction-induced non-Hermitian aggregation effects in Hilbert space are verified by measuring the spatial impedance response. Our finding not only discloses a physical effect in the non-Hermitian system but also suggests a flexible platform to further investigate other non-Hermitian correlated phases in experiments.

The dynamics of Hermitian many-body quantum systems has long been a challenging subject due to the complexity induced by the particle-particle interactions. In contrast, this difficulty may be avoided in a well-designed non-Hermitian system. The exceptional point (EP) in a non-Hermitian system admits a peculiar dynamics: the final state being a particular eigenstate, coalescing state. In this work, we study the dynamic transition from a trivial insulating state to an $\eta$-pairing state in a composite non-Hermitian Hubbard system. The system consists of two subsystems, A and B, which are connected by unidirectional hoppings. We show that the dynamic transition from an insulating state to an $\eta$-pairing state occurs by the probability flow from A to B: the initial state is prepared as an insulating state of A, while B is left empty. The final state is an $\eta$-pairing state in B but empty in A. Analytical analyses and numerical simulations show that the speed of relaxation of the off-diagonal long-range order pair state depends on the order of the EP, which is determined by the number of pairs and the fidelity of the scheme is immune to the irregularity of the lattice.

The notion of a band inversion provides an intuitive physical paradigm for understanding the electronic band topology. Here we study the general band inversion mechanism, which exploits local atomic orbitals and lattice symmetry, in mirror protected topological crystalline insulators (TCIs). Based on low-energy effective theory analysis, we find that for these mirror protected TCIs, the topological invariant (i.e., the mirror Chern number ${\mathcal{C}}_M$) is determined by the difference of total magnetic quantum numbers $m_j$ of orbitals involved in the band inversion: $|{\mathcal{C}}_M|=|\mathrm{\Delta }{m}_j|$. This angular-momentum criterion is further verified by the atomic tight-binding model calculations in two-dimensional (2D) crystalline, quasicrystalline, and disordered lattices. Moreover, such an angular momentum invoked band inversion (AMBI) is also extendable to 3D lattices and gives rise to topological semimetals with Dirac points in the bulk and double Fermi arcs on surfaces. As a concrete material example, we further predict that the Ba monolayer is an AMBI-induced TCI by first-principles calculations. In addition, we also show that a large number of previously proposed TCI materials satisfy the AMBI mechanism. Our findings not only provide an alternative understanding of mirror protected band topology but also offer useful guidance for designing or engineering mirror protected TCI materials.

Heavy-fermion family exhibits fascinating and often puzzling properties due to the presence of open-shell $f$ ions and the complexity of the associated charge, orbital, and spin degrees of freedom. ${\mathrm{SmB}}_6$ is a prototypical heavy-fermion compound that is electrically insulating but yet it displays quantum oscillations, which are a telltale signature of the metallic state. Adding to the enigma is the possibility that ${\mathrm{SmB}}_6$ is a topological Kondo insulator. Here, by treating the spin degree of freedom on an equal footing with other degrees of freedom using the parameter-free strongly constrained and appropriately normed (SCAN) density functional, we explore the ground-state electronic structure of ${\mathrm{SmB}}_6$. A number of competing magnetic phases lying very closely in energy are found, indicating the key role of spin fluctuations in the material. The computed band structure, crystal-field splittings in the $f$-electron complex, the heavy effective electron mass at the Fermi energy, and the large specific heat are all in good agreement with the corresponding experimental results. In particular, our predicted FS explains the experimentally observed bulk quantum oscillations as well as the low electrical conductivity of ${\mathrm{SmB}}_6$. The topological Kondo state of ${\mathrm{SmB}}_6$ is shown to be robust regardless of its magnetic configuration. The excellent performance of SCAN in heavy-fermion systems is explained in terms of its ability to treat self-interaction errors and symmetry breaking within the framework of the density functional theory. Our study provides a new approach for modeling heavy-fermion materials.

The pressure-induced isostructural insulator-to-metal transition for SmS is characterized by the presence of an intermediate valence state at higher pressure which cannot be captured by density functional theory. As a direct outcome of including the charge and spin fluctuations incorporated in dynamical mean-field theory, we see the emergence of insulating and metallic phases with increasing pressure as a function of changing valence. This is accompanied by significantly improved predictions of the equilibrium lattice constants and bulk moduli for all Sm monochalcogenides verifying experiments. Nudged elastic band analysis reveals the insulating states to have a finite quasiparticle weight, decreasing as the gap closes rendering the transition to be not Mott-like, and classifies these materials as correlated band insulators. The difference between the discontinuous and continuous natures of these transitions can be attributed to the closeness of the sharply resonant Sm-4$f$ peaks to the Fermi level in the predicted metallic states in SmS compared with SmSe and SmTe.

A general expression for the orbital magnetization of a Floquet system is derived. The expression holds for a clean system and is valid for any driving protocol and arbitrary occupation of the bands. The orbital magnetization is shown to be large not only for Chern insulators, but also for anomalous phases where the Chern number does not fully account for the topology. In addition, the orbital magnetization is shown to take significant values both for a thermal equilibrium occupation of the Floquet bands and for occupations determined by a quantum quench from an initial state with zero orbital magnetization. For the latter case, the orbital magnetization is shown to be highly sensitive to van Hove singularities of the Floquet bands.

Transition metal sulfide halides such as ${\mathrm{Mo}}_2{\mathrm{SBr}}_2$ have exhibited excellent anisotropy in their electronic and optical properties. To explore the mechanism behind this strong anisotropic behavior, we performed first-principles calculations on the anisotropic mechanical, optical, and electronic properties of monolayer ${\mathrm{Mo}}_2{\mathrm{SBr}}_2$. We find that monolayer ${\mathrm{Mo}}_2{\mathrm{SBr}}_2$ demonstrates obvious anisotropy in its electron mobility, ${\mu }_e$, with an extremely high ${\mu }_e$ of $10,356.08\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{–1}{\mathrm{s}}^{–1}$ along the $b$ direction. We attributed this strong anisotropy in monolayer ${\mathrm{Mo}}_2{\mathrm{SBr}}_2$ to the unique characters in the orbital coupling. Our further studies show that direct $d\text{−}d$ coupling between the nearest-neighboring Mo atoms plays a critical role in the unique carrier transport properties and strong anisotropy. Direct $d\text{−}d$ coupling provides a fast hole transport channel along the $c$ direction. Furthermore, wavefunction delocalization at the valence band maximum is significantly enhanced by this $d\text{−}d$ hybridization, which further reduces the effective mass of holes. Our work provides physical insights into the origin of strong anisotropy in the photoelectric properties of transition metal sulfide halides. Transition metal sulfide halides are demonstrated to have great potential applications in novel nanoelectronic devices.

The valence flat bands in transition metal dichalcogenide (TMD) heterobilayers are shown to exhibit strong intralayer spin-orbit coupling. I show that symmetry constrains the spin-dependent complex phase of hopping terms in an effective tight-binding model of the valence flat bands. A perpendicular electric field causes interlayer hybridization, such that the effective model becomes equivalent to the Kane-Mele model of topological insulators. The proposed model can be used as a starting point to understand interactions and the experimentally observed topological transitions.

Over the last decade, conditions for perfect state transfer in quantum spin chains have been discovered and their experimental realizations addressed, as have their extensions to more complex geometries of coupled cavity-emitter arrays. In this paper we further consider such studies and situations in which quantum state transfer can occur with high fidelity, even when the cavity-cavity coupling rates and cavity-emitter interaction rates are comparable. This is accomplished through the development and use of a Monte Carlo approach to the inverse eigenvalue problem, which allows the determination of coupling rates which optimize quantum state transfer fidelity and subsequent time evolution of the polariton wave function through exact diagonalization of the resulting Jaynes-Cummings-Hubbard Hamiltonian. The effect of inhomogeneous emitter locations is also evaluated. Our key results include the demonstration that our methodology can be used successfully to establish Hamiltonian parameters for high-fidelity state transfer in more general lattice geometries and excitation number sectors, and also a determination of the effects of fluctuations in those parameters about their optimal values.

The nonequilibrium Casimir-Polder force between a nanoparticle and a graphene sheet kept at different temperatures is investigated in the framework of a Dirac model using the formalism of the polarization tensor. It is shown that the force magnitude increases with increasing temperature of a graphene sheet. At larger separations an impact of nonequilibrium conditions on the force becomes smaller. According to our results, the attractive Casimir-Polder force vanishes at some definite nanoparticle-graphene separation and becomes repulsive at larger separations if the temperature of a graphene sheet is smaller than that of the environment. This effect may find applications both in fundamental investigations of graphene and for the control of forces in microdevices of bioelectronics.

In topological semimetals and insulators, negative longitudinal magnetoresistance and angle-dependent planar Hall effect have been reported arising from the Berry curvature. Using the Boltzmann transport theory, we present a closed-form expression for the nonequilibrium distribution function, which includes both the effects of the Berry curvature and Lorentz force. Using this formulation, we obtain analytical expressions for conductivity and resistivity tensors in Weyl semimetals demonstrating a characteristic field dependence arising from the competition between the two effects.

We investigate the coupled dynamics of charge and energy in interacting lattice models with dipole conservation. We formulate a generic hydrodynamic theory for this combination of fractonic constraints and numerically verify its applicability to the late-time dynamics of a specific bosonic quantum system by developing a microscopic nonequilibrium quantum field theory. Employing a self-consistent $1/N$ approximation in the number of field components, we extract all entries of a generalized diffusion matrix and determine their dependence on microscopic model parameters. We discuss the relation of our results to experiments in ultracold atom quantum simulators.

We investigate the electronic structure of a Kondo lattice system, ${\mathrm{CeCuSb}}_2$ exhibiting significant mass enhancement and Kondo-type behavior. We observe multiple features in the hard x-ray photoemission spectra of Ce core levels due to strong final-state effects. The depth-resolved data exhibit a significant change in relative intensity of the features with the surface sensitivity of the probe. The extracted surface and bulk spectral functions are different and exhibit a Kondo-like feature at higher binding energies in addition to the well and poorly screened features. The core-level spectra of Sb exhibit huge and complex changes as a function of the surface sensitivity of the technique. The analysis of the experimental data suggests that the two nonequivalent Sb sites possess different electronic structures and in each category, the Sb layers close to the surface are different from the bulk ones. An increase in temperature influences the Ce-Sb hybridization significantly. The plasmon–excitation-induced loss features are also observed in all core-level spectra. All these results reveal the importance of Ce-Sb hybridizations and indicate that the complex renormalization of Ce-Sb hybridization may be the reason for the exotic electronic properties of this system.

Electron spin oriented along an external magnetic field is subject to longitudinal spin relaxation with characteristic time $T_1$. The corresponding decay is nonoscillating, so one cannot readily ascribe $T_1$ to a certain $g$ factor. This becomes a problem when several electronic states with different $g$ factors are present in the system, e.g., electrons and holes. We solve this problem by optically pumping spin polarization and then selectively depolarizing it using a radio frequency (rf) field. By modulating the rf field amplitude one can observe the retarded modulation of spin polarization which depends on the relation between the modulation period and $T_1$. Using this resonant spin inertia method, we unveil the strong anisotropy of $T_1$ for rare-earth ${\mathrm{Ce}}^{3+}$ ions in a YAG crystal at low temperatures and low magnetic fields. We also show that the spread of Larmor frequencies within the electron ensemble in this system is not static, but results from the fluctuations of internal magnetic fields on a timescale much shorter than $T_1$.

We introduce a method based on matrix product states (MPS) for computing spectral functions of (quasi-) one-dimensional spin chains, working directly in momentum space in the thermodynamic limit. We simulate the time evolution after applying a momentum operator to an MPS ground state by working with the momentum superposition of a window MPS. We show explicitly for the spin-1 Heisenberg chain that the growth of entanglement is smaller in momentum space, even inside a two-particle continuum, such that we can attain very accurate spectral functions with relatively small bond dimension. We apply our method to compute spectral lineshapes of the gapless XXZ chain and the square-lattice $J_1-J_2$ Heisenberg model on a six-leg cylinder.

We perform a comparative $2\times 2$ real space cluster DMFT study on minimal models for ${\mathrm{NdNiO}}_2$ and ${\mathrm{CaCuO}}_2$ obtained from downfolding DFT states, using a Nambu formalism that allows for both superconducting and antiferromagnetic order. We produce a phase diagram in temperature and doping. We find that for the nickelate, like the cuprate, the stoichiometric compound is antiferromagnetic. We find superconductivity in a doping range bounded, with a small coexistence region, by the onset of antiferromagnetism at low doping and with transition temperature becoming immeasurably small at high doping. Superconductivity emerges at around the same hole doping for both compounds, but requires a larger deviation from half-filling for the nickelate. Both antiferromagnetic and superconducting order lead to a partial gapping of the $d_{x^2-y^2}$ Fermi surface sheet. Our similar results for the cuprate and nickelate suggest that nickelate superconductivity is cupratelike. We compare our results to the experimental phase diagram.

Due to its rotation, Earth traps a few equatorial ocean and atmospheric waves, including Kelvin, Yanai, Rossby, and Poincaré modes. It has been recently demonstrated that the mathematical origin of equatorial waves is intricately related to the nontrivial topology of hydrodynamic equations describing oceans or the atmosphere. In the present work, we consider plasma oscillations supported by a two-dimensional electron gas confined at the surface of a sphere or a cylinder. We argue that in the presence of a uniform magnetic field, these systems host a set of equatorial magnetoplasma waves that are counterparts to the equatorial waves trapped by Earth. For a spherical geometry, the equatorial modes are well developed only if their penetration length is smaller than the radius of the sphere. For a cylindrical geometry, the spectrum of equatorial modes is weakly dependent on the cylinder radius, and it overcomes finite-size effects. We argue that this exceptional robustness can be explained by destructive interference effects. We discuss possible experimental setups, including grains and rods composed of topological insulators (e.g., ${\text{Bi}}_2{\text{Se}}_3$) or metal-coated dielectrics (e.g., ${\text{Au}}_2\text{S}$).

The magnetoelectric effect and skyrmions are two fundamental phenomena in the field of condensed-matter physics. Here, using first-principles calculations and Monte Carlo simulations, we propose that strong magnetoelectric coupling can be demonstrated in a multiferroic heterobilayer consisting of two-dimensional (2D) MnSTe and $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$. As the electric polarization in ferroelectric $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ is switched, the creation and annihilation of the topological magnetic phase can be achieved in this multiferroic heterobilayer, giving rise to the intriguing ferroelectrically controllable skyrmions. This feature is further revealed to be closely related to the physical quantity of $D^2/\left|KJ\right|$, which is generally applicable for describing the required conditions of such physics. Moreover, the evaluations of their topological magnetic phases with temperature are systematically discussed. These insights not only greatly enrich the research on 2D magnetoelectric multiferroics, but also pave a promising avenue to realize new skyrmionic device concepts.

The solid Earth's inner core (IC) is a sphere with a radius of about 1300 km in the center of the Earth. The information about the IC comes mainly from seismic studies. The composition of the IC is obtained by matching the seismic data and properties of candidate phases subjected to high pressure (P) and temperature (T). The close match between the density of the IC and iron suggests that the main constituent of the IC is iron. However, the stable phase of iron is still a subject of debate. One such iron phase, the body-centered cubic phase (bcc), is dynamically unstable at pressures of the IC (330–364 GPa) and low T but gets stabilized at high T characteristic of the IC (5000–7000 K). So far, ab initio molecular dynamics (AIMD) studies attempted to compute the bcc elastic properties for a small (order of ${10}^2$) number of atoms. The mechanism of the bcc stabilization cannot be enabled in such cells and that has led to erroneous results. Here we apply AIMD to compute elastic moduli and sound velocities of the Fe bcc phase for a 2000 Fe atom computational cell, which is a cell of unprecedented size for ab initio calculations of iron. Unlike in previous ab initio calculations, both the longitudinal and the shear sound velocities of the Fe bcc phase closely match the properties of the IC material at P = 360 GPa and T = 6600 K, likely the PT conditions in the IC. The calculated density of the bcc iron at these PT conditions is just $3\%$ higher than the density of the IC material according to the Preliminary Earth Model. This suggests that the widely assumed amount of light elements in the IC may need a reconsideration. The anisotropy of the bcc phase is an exact match to the most recent seismic studies.

The chiral anomaly may be realized in condensed matter systems with pairs of Weyl points. Here we show that the chiral anomaly can be realized in diverse noncentrosymmetric systems even without Weyl point pairs when spin-orbit coupling (SOC) induces nonzero Berry curvature flux through Fermi surfaces (FS). This motivates the condensed matter chiral anomaly to be interpreted as a FS property rather than a Weyl point property. The SOC-induced anomaly reproduces the well-known charge transport properties of the chiral anomaly such as the negative longitudinal magnetoresistance and the planar Hall effect in Weyl semimetals. Since it is of SOC origin, it also affects the spin transport and gives rise to anomaly induced longitudinal spin currents and the magnetic spin Hall effect, which are absent in conventional Weyl semimetals.