The long-time dynamics of quantum systems, typically, but not always, results in a thermal steady state. The microscopic processes that lead to or circumvent this fate are of interest, since everyday experience tells us that not all spatial regions of a system heat up or cool down uniformly. This motivates the question: Under what conditions can one slow down or completely arrest thermalization locally? Is it possible to construct realistic Hamiltonians and initial states such that a local region is effectively insulated from the rest, or acts as a barrier between two or more regions? We answer this in the affirmative by outlining the conditions that govern the flow of energy and entropy between subsystems. Using these ideas we provide a representative example for how simple quantum few-body states can be used to engineer a “thermal switch” between interacting regions.

Magnetic materials host a wealth of nonlinear dynamics, textures, and topological defects. This is possible due to the competition between strong nonlinearity and dispersion, which act at the atomic scale, as well as long-range interactions. However, these features are difficult to study analytically and numerically because of the vastly different temporal and spatial scales involved. Here, we present a pseudospectral approach for the Landau-Lifshitz equation that invokes energy and momentum conservation embodied in the magnon dispersion relation to accurately describe both atomic and continuum limits. Furthermore, this approach enables analytical study at every scale. We show the applicability of this model in both the continuum and atomic limit by investigating modulational instability and ultrafast evolution of magnetization due to transient grating, respectively, in a one-dimensional ferromagnetic chain with perpendicular magnetic anisotropy. This model provides the possibility of grid-independent multiscale numerical approaches that will enable the description of singularities within a single framework.

We propose to implement tunable higher-order topological states in a heterojunction consisting of a two-dimensional (2D) topological insulator and the recently discovered altermagnets, whose unique spin-polarization in both real and reciprocal space and null magnetization are in contrast to conventional ferromagnets and antiferromagnets. Based on symmetry analysis and effective edge theory, we show that the special spin splitting in altermagnets with different symmetries, such as $d$ wave, can introduce Dirac mass terms with opposite signs on the adjacent boundaries of the topological insulator, resulting in the higher-order topological state with mass-domain-bound corner states. Moreover, by adjusting the direction of the Néel vector, we can manipulate such topological corner states by moving their positions. By first-principles calculations, taking a 2D topological insulator bismuthene with a square lattice on an altermagnet ${\mathrm{MnF}}_2$ as an example, we demonstrate the feasibility of creating and manipulating the higher-order topological states through altermagnets. Finally, we discuss the experimental implementation and detection of the tunable topological corner states, as well as the potential non-Abelian braiding of the Dirac corner fermions.

We calculate the miscibility gap in mixtures of hydrogen and water under high-temperature and high-pressure conditions as relevant for planetary interiors with density functional theory combined with classical molecular dynamics. In contrast to earlier calculations, we find a miscibility gap at temperatures below 1500–2000 K at pressures of up to 300 kbar, which extends the experimentally known immiscibility region by one order of magnitude in pressure. In contrast to extrapolated experimental demixing lines reaching to high temperatures, our results indicate a termination of the demixing region close to 2000 K. This finding profoundly impacts the understanding of the interiors of ice-giant planets such as Neptune and Uranus by supporting a partially demixed interior, including a density discontinuity near 2000 K, which corresponds to planetary radii of 0.85–0.95 in Uranus and Neptune. Additionally, our findings are relevant for thermal evolution models of Earth that aim to explain the formation of superreducing mineral associations.

The noncollinear spin textures provide promising avenues to stabilize exotic magnetic phases and excitations. They have attracted vast attention in the past decades due to their nontrivial band topology. Distinct from the conventional route of involving the Dzyaloshinskii-Moriya interaction in a honeycomb magnet, the interplay of bond-dependent Kitaev and $\mathrm{\Gamma }$ interactions, originating from the spin-orbit coupling and octahedra crystal field in real materials, has demonstrated to be another source to generate noncollinear spin textures with multiple spins in a magnetic unit cell. Notably, earlier works have revealed a triple-meron crystal (TmX) consisting of 18 spins in the frustrated Kitaev-$\mathrm{\Gamma }$ model. Aligning with previous efforts, here we attempt to identify that the TmX hosts several peculiar features with the help of the linear spin-wave theory. To begin with, the symmetric anisotropic exchanges are beneficial for the existence of nonreciprocal magnons, which are stabilized by an external magnetic field. Further, within the regime of TmX, successive topological phase transitions occur, accompanied by the changes of Chern number in value and thermal Hall conductivity in sign. In addition, the topological nature of magnons is also verified by the onset of chiral edge modes in a nanoribbon geometry. Our findings pave the way to study topological phenomena of noncollinear spin textures in potential Kitaev materials.

We investigate the boundary effects that arise when spin-$\frac{1}{2}$ impurities interact with the edges of the antiferromagnetic spin-$\frac{1}{2}$ Heisenberg chain through spin exchange interactions. We consider both cases when the couplings are ferromagnetic or antiferromagnetic. We find that in the case of antiferromagnetic interaction, when the impurity coupling strength is much weaker than that in the bulk, the impurity is screened in the ground state via the Kondo effect. The Kondo phase is characterized by the Lorentzian density of states and a dynamical scale, the Kondo temperature $T_K$, is generated. As the impurity coupling strength increases, $T_K$ increases until it reaches its maximum value $T_0=2\pi J$ which is the maximum energy carried by a single spinon. When the impurity coupling strength is increased further, we enter another phase, the bound mode phase, where the impurity is screened in the ground state by a single particle bound mode exponentially localized at the edge to which the impurity is coupled. We find that, in contrast to the Kondo phase, the impurity can be unscreened by unoccupying the single particle bound mode. This costs an energy $E_b$ that is greater than $T_0$. There exists a boundary eigenstate phase transition between the Kondo and the bound-mode phases, a transition which is characterized by the change in the number of towers of the Hilbert space. The transition also manifests itself in local thermodynamic quantities—local impurity density of states and the local impurity magnetization in the ground state. When the impurity coupling is ferromagnetic, the impurity is unscreened in the ground state; however, when the absolute value of the ratio of the impurity and bulk coupling strengths is greater than $\frac{4}{5}$, the impurity can be screened by adding a bound mode that costs energy greater than $T_0$. When two impurities are considered, the phases exhibited by each impurity remain unchanged in the thermodynamic limit, but nevertheless the system exhibits a rich phase diagram.

This paper presents a method to detect time-reversal symmetry breaking in noncentrosymmetric superconductors using only transport measurements. Specifically, if time-reversal symmetry is broken via a phase difference between singlet and triplet correlations, as in anapole superconductors, the differential conductance in superconductor-ferromagnet-normal metal junctions is enhanced by increasing the exchange field strength in the ferromagnet. This is in sharp contrast with the negative magnetoresistance when using superconductors in which time-reversal symmetry is preserved. Moreover, results show a large quadrupolar component of the magnetoresistance which is qualitatively different from the bipolar giant magnetoresistance in strong ferromagnets.

We report a theoretical analysis of x-ray magnetic circular dichroism (XMCD) at the Cr-$L$ edge in half-metallic ferromagnetic ${\mathrm{CrO}}_2$. First, since the XMCD spectrum is the difference between the x-ray absorption spectra (XAS) for right- and left-handed circularly polarized x rays, a general perturbative method of calculating XAS spectra is developed by means of the Keldysh Green's function technique for nonequilibrium states. Subsequently, it is applied to the analysis of XMCD of half-metallic ferromagnetic ${\mathrm{CrO}}_2$. Calculated XAS and XMCD spectra are compared with several previous experimental data. It is clearly shown that effects of the atomiclike Coulomb interaction between the $2p$ and $3d$ states are indispensable ingredients to yield good agreement with the experiments. Such strong $2p\text{−}3d$ correlation may originate from a peculiarity of the half-metallic ferromagnetic state. Evaluation of the validity of sum rules is made within our framework.

A chiral symmetric Su-Schrieffer-Heeger (SSH) chain features topological end states in one of its dimerized configurations. Those midgap zero-energy states show interesting modifications upon a periodic tuning of the hopping modulations. In addition, more and more in-gap end modes appear at nonzero energies for further partitioning of the Brillouin zone (BZ) due to increased hopping periodicity. These topological phases are identified with a detailed analysis of the topological invariants, namely, winding number and Zak phases. The spectra and topology of these systems with periodically modulated hopping are also studied in the presence of a single static domain wall, separating two topologically inequivalent dimerized structures. The domain wall causes additional in-gap modes in the spectrum as well as zero-energy domain-wall solitonic states for specific hopping periodicities. We also study the effect of disorder, particularly the chirality breaking on-site ones, on the edge and domain-wall states. Other than the SSH type, we also consider random, Rice-Mele, or AI-type disorder to do a comparative analysis of the evolution of chirality and zero-energy states as the strength of disorder and hopping periodicity is varied. Our findings can add important feedback in utilizing topological phases in various fields including quantum computations, while the results can be easily verified in a cold atom setup within optical lattices.

A quantum coherent screening cloud around a magnetic impurity in metallic systems is the hallmark of the antiferromagnetic Kondo effect. Despite the central role of the Kondo effect in quantum materials, the structure of quantum correlations of the screening cloud has defied direct observations. In this work, we introduce a machine-learning algorithm that allows one to spatially map the entangled electronic modes in the vicinity of the impurity site from experimentally accessible data. We demonstrate that local correlators allow reconstruction of the local many-body correlation entropy in real space in a double Kondo system with overlapping entanglement clouds. Our machine-learning methodology allows bypassing the typical requirement of measuring long-range nonlocal correlators with conventional methods. We show that our machine-learning algorithm is transferable between different Kondo system sizes, and we show its robustness in the presence of noisy correlators. Our work establishes the potential machine-learning methods to map many-body entanglement from real-space measurements.

In strongly correlated metals, long-range magnetic order is sometimes found only upon introduction of a minute amount of disordered nonmagnetic impurities to the unordered clean samples. To explain such anti-intuitive behavior, we propose a “rekindled failed-order” scenario of inducing electronic (magnetic, orbital, or charge) order via chemical or lattice disorder in systems with coexisting local moments and itinerant carriers. By disrupting the damaging long-range quantum fluctuation originating from the itinerant carriers, the electronic order preferred by the local moment can be reestablished. We demonstrate this mechanism using a realistic spin-fermion model and show that the magnetic order can indeed be recovered as a result of enhanced disorder once the length scale of phase coherence of the itinerant carriers becomes shorter than a critical value. The proposed simple idea has a general applicability to strongly correlated metals, and it showcases the rich physics resulting from interplay between mechanisms of multiple length scales.

Unlike unitary dynamics, measurements of a subsystem can induce long-range entanglement via quantum teleportation. The amount of measurement-induced entanglement or mutual information depends jointly on the measurement basis and the entanglement structure of the state (before measurement), and has operational significance for whether the state is a resource for measurement-based quantum computing, as well as for the computational complexity of simulating the state using quantum or classical computers. In this paper, we examine entropic measures of measurement-induced entanglement (MIE) and information (MII) for the ground states of quantum many-body systems in one and two spatial dimensions. From numerical and analytic analysis of a variety of models encompassing critical points, quantum Hall states, string-net topological orders, and Fermi liquids, we identify universal features of the long-distance structure of MIE and MII that depend only on the underlying phase or critical universality class of the state. We argue that, whereas in 1D the leading contributions to long-range MIE and MII are universal, in 2D, the existence of a teleportation transition for finite-depth circuits implies that trivial 2D states can exhibit long-range MIE, and the universal features lie in subleading corrections. We introduce modified MIE measures that directly extract these universal contributions. As a corollary, we show that the leading contributions to strange correlators, used to numerically identify topological phases, are in fact nonuniversal in two or more dimensions, and explain how our modified constructions enable one to isolate universal components. We discuss the implications of these results for classical- and quantum- computational simulation of quantum materials.

We study the local electronic structure of an equimolar-multimetal solid solution of high-entropy metal disulfide $\left(\mathrm{Fe},\mathrm{Co},\mathrm{Ni},\mathrm{Cu}\right){\mathrm{S}}_2$ and its parent compounds ${M\mathrm{S}}_2$ $(M=\mathrm{Fe}, \mathrm{Co}, \mathrm{Ni}, \text{and} \mathrm{Cu})$ using x-ray absorption spectroscopy (XAS). The Fe, Co, and Ni $L_{2,3}$-edge absorption spectra indicate a divalent metal state both in ${(\mathrm{Fe}, \mathrm{Co}, \mathrm{Ni}, \mathrm{Cu})\mathrm{S}}_2$ and its parent compounds, except for the Cu $L_{2,3}$-edge absorption spectra. The Cu $L_{2,3}$-edge spectra of ${\mathrm{CuS}}_2$ and $\left(\mathrm{Fe},\mathrm{Co},\mathrm{Ni},\mathrm{Cu}\right){\mathrm{S}}_2$ show satellites, which rule out the divalent Cu but can be analyzed as a combination of monovalent and trivalent copper states. The $L_{2,3}$-edge XAS spectral analysis with charge-transfer multiplet cluster model calculations was carried out for $\left(\mathrm{Fe},\mathrm{Co},\mathrm{Ni},\mathrm{Cu}\right){\mathrm{S}}_2$ and its parent compounds. The estimated electronic parameters indicate a negative charge-transfer energy for the parent compounds and high-entropy compound (with the Ni L edge in the high-entropy compound being an exception), which corresponds to a p-p type lowest energy excitation in the extended Zaanen-Sawatzky-Allen phase diagram. The analysis shows that the charge-transfer energy $\mathrm{\Delta }$ decreases and the on-site Coulomb energy $U_{dd}$ increases systematically from Fe to Cu. The results suggest that in the high-entropy compound compared to the parent compounds, the hybridization strengths are weaker for Fe $3d\text{−}\mathrm{S}$ $3p$ and Co $3d\text{−}\mathrm{S}$ $3p$ and stronger for Ni $3d\text{−}\mathrm{S}$ $3p$ and Cu $3d\text{−}\mathrm{S}$ $3p$ bonds. This behavior is consistent with the longer Fe-S and Co-S bond distances and shorter Ni-S and Cu-S bond distances in the high-entropy compound compared to the parent compounds. The results indicate modifications in the structural lattice parameters of the high-entropy compound are reflected in the electronic structure and provides evidence for the so-called cocktail effect in the high-entropy compound.

The highest superconducting transition temperature in Nb among elemental materials facilitates applications of superconducting junctions. Nonetheless, its surface forms self-organized oxide structures, which hinders the preparation of well-defined interfaces. We investigated the atomic structure of oxygen-induced $\mathrm{Nb}\left(110\right)$ surfaces, aiming to define the substrates for such interfaces. The atomic force microscopy and scanning tunneling microscopy measurements visualized two rows of apparently low-lying Nb and three rows of O between Nb chains. An optimized model structure is proposed based on density-functional theory calculations. Analysis of the Bader charge and the density of states clarified how the atoms appear in the microscopies.

We present a detailed theoretical investigation on the electronic transport properties of $n$-type monolayer (ML) transition metal dichalcogenides (TMDs) at low temperature in the presence of proximity-induced interactions such as Rashba spin-orbit coupling (RSOC) and the exchange interaction. The electronic band structure is calculated by solving the Schrödinger equation with a $\mathbf{k}·\mathbf{p}$ Hamiltonian, and the electric screening induced by electron-electron interaction is evaluated under a standard random phase approximation approach. In particular, the longitudinal and transverse or Hall mobilities are calculated by using a momentum-balance equation derived from a semiclassical Boltzmann equation, where the electron-impurity interaction is considered as the principal scattering center at low temperature. The obtained results show that the RSOC can induce the in-plane spin components for spin-split subbands in different valleys, while the exchange interaction can lift the energy degeneracy for electrons in different valleys. The opposite signs of Berry curvatures in the two valleys would introduce opposite directions of Lorentz force on valley electrons. As a result, the transverse currents from nondegenerate valleys can no longer be canceled out so that the transverse current or Hall mobility can be observed. Interestingly, we find that at a fixed effective Zeeman field, the lowest spin-split conduction subband in ML-TMDs can be tuned from one in the $K^{\prime }$-valley to one in the $K$-valley by varying the Rashba parameter. The occupation of electrons in different valleys also varies with changing carrier density. Therefore, we can change the magnitude and direction of the Hall current by varying the Rashba parameter, effective Zeeman field, and carrier density by, e.g., the presence of a ferromagnetic substrate and/or applying a gate voltage. By taking the ML-${\mathrm{MoS}}_2$ as an example, these effects are demonstrated and examined. The important and interesting theoretical findings can be beneficial to experimental observation of the valleytronic effect and to gaining an in-depth understanding of the ML-TMD systems in the presence of proximity-induced interactions.

Higher-order topological insulators in two spatial dimensions display fractional corner charges. While fractional charges in one dimension are known to be captured by a many-body bulk invariant, computed by the Resta formula, a many-body bulk invariant for higher-order topology and the corresponding fractional corner charges remains elusive despite several attempts. Inspired by recent work by Tada and Oshikawa [arXiv:2302.00800], we propose a well-defined, many-body bulk invariant for $C_n$-symmetric higher-order topological insulators that is valid for both noninteracting and interacting systems. Instead of relating them to the bulk quadrupole moment as was previously done, we show that in the presence of $C_n$ rotational symmetry, this bulk invariant can be directly identified with quantized fractional corner charges. In particular, we prove that the corner charge is quantized as $e/n$ with $C_n$ symmetry, leading to a ${\mathbb{Z}}_n$ classification for higher-order topological insulators in two dimensions.