We study the effects of quenched disorder in a class of quantum chains with ($p+1$)-multispin interactions exhibiting a free fermionic spectrum, paying special attention to the case $p=2$. Depending if disorder couples to (i) all the couplings or just to (ii) some of them, we have two distinct physical scenarios. In case (i), we find that the transitions of the model are governed by a universal infinite-randomness critical point surrounded by quantum Griffiths phases similarly as happens to the random transverse-field Ising chain. In case (ii), we find that quenched disorder becomes an irrelevant perturbation: the clean critical behavior is stable and Griffiths phases are absent. Beyond the perturbative regime, disorder stabilizes a line of finite-randomness critical points (with nonuniversal critical exponents), that ends in a multicritical point of infinite-randomness type. In that case, quantum Griffiths phases also appear surrounding the finite-disorder transition point. We have characterized the correlation functions and the low-temperature thermodynamics of these chains. Our results are derived from a strong-disorder renormalization-group technique and from finite-size scaling analysis of the spectral gap computed exactly (up to sizes $\sim {10}^7$) via an efficient new numerical method recently introduced in the literature [Phys. Rev. B 104, 174206 (2021)].

The discovery of built-in and synthetic Rashba fields in Si spin channels [S. Lee et al., Nat. Mater. 20, 1228 (2021)] challenged the conventional understanding of spin transport physics in semiconducting materials and forced researchers to reconsider the procedures used for estimating spin drift velocity and spin mobility. A conventional procedure for the estimation involves the detection of the Hanle-type spin precession under the application of an external magnetic field perpendicular to the plane; however, the in-plane effective magnetic fields due to the built-in Rashba fields hamper precise estimation because of the additional spin precession. In this work, we establish a precise method to estimate spin drift velocity and spin mobility, in addition to the spin lifetime and spin diffusion constant, by appropriately tuning the Rashba fields. Beyond the emblematic case of Si, the established method can be applied to other semiconductors, such as Ge and GaAs.

We introduce and explore the magnetization behavior in a quantum spin system on a cactus graph, deemed the cactus graph model, featuring an exact dimer singlet ground state. We analyze the singlet-triplet gap, interactions among excited triplets, and correlated hopping under an external magnetic field using a strong coupling expansion. Employing an effective hard-core boson representation, we unveil density wave magnetization plateaus and supersolid phases, revealing the intricate interplay between interactions and hopping dynamics. Furthermore, we conjecture that correlated hopping gives rise to multitriplet bound states, and potentially engendering to the stabilization of additional low-lying magnetization plateaus.

We theoretically propose a mechanism to realize the superconducting diode effect (SDE): The current can generate a magnetic field, affecting the magnetic moment of magnetic impurity. When the connection region of the Josephson junction is coupled with the magnetic impurity, the supercurrents in positive and negative directions have different influences on the magnetic moment. This results in a phenomenon that the critical supercurrents in these opposite directions are unequal, which is called SDE. We model the Josephson connection region by a quantum dot. Then the critical supercurrents are investigated by the nonequilibrium Green's function method, and we carry out a detailed symmetry analysis on the supercurrent relations. The calculation results confirm that the SDE does exist in this system. In addition, the SDE is significant in a wide parameter space and can be effectively adjusted in various ways. Our design only demands a magnetic impurity and conventional superconductors. The unconventional finite-momentum Cooper pair and spin-orbit coupling are not required, and there is also no need for the existence of chirality or an external magnetic field. Our work provides a universal device structure for the development of superconducting electronics.

Revealing local lattice distortions in physical systems is nontrivial, largely because such structural features often are not necessarily amenable to traditional crystallographic investigations. This poses limits to our understanding of the underlying physics, particularly in the case of strongly correlated systems where structural, electronic, and magnetic degrees of freedom are intertwined. Using resonant total x-ray scattering coupled to differential pair distribution function analysis, we reveal the presence of pronounced local lattice distortions in the square net Pt planes in the prototypical strongly correlated $A{\mathrm{Pt}}_2{\mathrm{X}}_2$ intermetallics ($A=\mathrm{U}$, Ce, or La and $X=\mathrm{Si}$ or Ge). The distortions are present before charge density wave, magnetic, Kondo lattice coherence, and/or superconducting orders emerge in these materials and, as density functional calculations suggest, are likely to affect them. Our study sheds light on the poorly known interactions between electronic orders and structural disorder in strongly correlated systems. It also demonstrates an advanced experimental approach to determine them that is relevant to any physical system showing deviations from perfect crystallinity.

Enhancing properties and performances of aluminium alloys by control of their solidification is pivotal in the automotive and aerospace industries. The fundamental role of the structure-diffusion relationship is investigated for Al-Mg-Si liquid alloys taken as a prototype of Al-6xxx. For this purpose, first principles based molecular dynamics simulations were performed for various Si and Mg content for Al-rich compositions, including the binary alloy counterparts. Results indicate that Mg and/or Si in alloys create a more compact ordering around Al in the alloy than the one existing in pure Al, thus lowering diffusion. Mg promotes icosahedral short-range order, while Si displays a preference towards cubic local ordering, impacting diffusion based on their respective content. It suggests a mechanism whereby an increase in Mg content generally lowers the diffusion of each species, whereas an increase in Si content enhances their diffusion, providing insights for future alloy design.

In transverse-field Ising models, disorder in the couplings gives rise to a drastic reduction of the critical energy gap and, accordingly, to an unfavorable, slower-than-algebraic scaling of the density of defects produced when the system is driven through its quantum critical point. By applying Kibble-Zurek theory and numerical calculations, we demonstrate in the one-dimensional model that the scaling of defect density with annealing time can be made algebraic by balancing the coupling disorder with suitably chosen inhomogeneous driving fields. Depending on the tail of the coupling distribution at zero, balancing can be either perfect, leading to the well-known inverse-square law of the homogeneous system, or partial, still resulting in an algebraic decrease but with a smaller, nonuniversal exponent. We also study defect production during an environment-temperature quench of the open variant of the model in which the system is slowly cooled down to its quantum critical point. According to our scaling and numerical results, uncorrelated disorder induces a logarithmic temporal decrease of the defect density, while balanced disorder leads again to an algebraic decay.

Nonreciprocal gyrotropic materials have attracted significant interest recently in material physics, nanophotonics, and topological physics. Most of the well-known nonreciprocal materials, however, only show nonreciprocity under a strong external magnetic field and within a small segment of the electromagnetic spectrum. Here, through first-principles density-functional theory calculations, we show that due to strong spin-orbit coupling manganese-bismuth (MnBi) exhibits nonreciprocity without any external magnetic field and a large gyrotropy in a broadband long-wavelength infrared regime. Further, we design a multilayer structure based on MnBi to obtain a maximum degree of spin-polarized thermal emission at 7 $\mu \mathrm{m}$. The connection established here between large gyrotropy and the spin-polarized thermal emission points to the potential use of MnBi to develop spin-controlled thermal photonics platforms.

A magnetic insulator is an ideal platform to propagate spin information by exploiting magnon currents. However, until now, most studies have focused on ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG) and a few other ferri- and antiferromagnetic insulators, but not on pure ferromagnets. In this study, we demonstrate that magnon currents can propagate in ferromagnetic insulating thin films of EuS. By performing both local and nonlocal transport measurements in 18-nm-thick films of EuS using Pt electrodes, we detect magnon currents arising from thermal generation by the spin Seebeck effect. By comparing the dependence of the local and nonlocal signals with the temperature (<30 K) and magnetic field (<9 T), we confirm the magnon transport origin of the nonlocal signal. Finally, we extract the magnon diffusion length in the EuS film $\left(\sim 140\mathrm{nm}\right)$, a short value in good correspondence with the large Gilbert damping measured in the same film.

We propose a minimal toy model for a two-dimensional altermagnet. The model unravels altermagnetic properties at a microscopic level. We find spin-split electron and nondegenerate magnon bands with a $d$-wave symmetry. We use the model to explore magnon-mediated superconductivity in altermagnets. The dominant superconducting state is spin polarized with a $p$-wave symmetry. The state adopts its characteristics from the spin-split electron bands. Furthermore, we find that the superconducting critical temperature of altermagnets can be significantly enhanced by tuning the chemical potential.

Using large-scale quantum Monte Carlo simulations, we determine the ground state phase diagram of the spin-1/2 antiferromagnetic Heisenberg model on the honeycomb lattice for the most generic case of three varying interaction strengths along the different lattice directions. We identify continuous quantum phase transition lines that separate the long-range ordered antiferromagnetic regime from three distinct quantum-disordered phases, each characterized by dominant dimer-singlet formations. The finite-size behavior along these phase transition lines exhibits anomalously large corrections to scaling, which we relate to similar recent findings in certain dimerized quantum spin systems and to singular one-dimensional limits in the model parameter space. We also comment more generally on the nonuniversality of critical cumulant ratios in anisotropic systems and attempts to restore universality by varying the aspect ratio.

Superconductors (SCs) with nontrivial topological band structures in the normal state have been discovered recently in bulk materials. When such SCs are made into thin films, quantum tunneling and Cooper pairing take place between the topological surface states (TSSs) on the opposing surfaces. Here, we find that chiral topological superconductivity with spontaneous time-reversal symmetry breaking emerges on the surface of such thin film SCs. There is a mirror symmetry that protects a novel nonunitary orbital and spin triplet pairing of the TSS. In the mirror diagonal space, the chiral topological SC manifests as two independent chiral $p$-wave spin-triplet pairing states, in which each is a two-dimensional superconducting analog of the Anderson-Brinkman-Morel state in superfluid ${}^3\mathrm{He}$ with in-plane exchange fields. A rich topological phase diagram governed by the nontrivial $\mathbb{Z}\oplus \mathbb{Z}$ topological invariant is obtained with gapless chiral Majorana edge modes and anyonic Majorana vortices. We further construct a three-dimensional lattice model with a topological band structure and SC pairings, which is motivated by Fe-based SCs such as Fe(Te,Se). We demonstrate the realization of the proposed intrinsic chiral topological superconductor in the quasi-two-dimensional thin-film limit. Our findings enable thin-film SCs with nontrivial $Z_2$ band structures as a single-material platform for intrinsic chiral topological superconductivity with both vortex and boundary Majorana excitations for topological quantum device making.

We propose a non-Hermitian (NH) interface system formed between two NH nodal line semimetals driven by optical fields as a platform for generation and tailoring of higher-order van Hove singularities (VHS). Through an analytical analysis of the density of states (DOS), we find VHS with logarithmic divergences in the Hermitian limit. Upon introducing NH terms, four exceptional rings on two sides of the Fermi line are formed. By tuning the NH parameters and the light amplitude, we find a situation when one exceptional ring crosses the Fermi line, where a saddle point appears and results in a paired VHS around the origin. In contrast, when an exceptional contour resides at the Fermi energy, the saddle points critically get destroyed and we obtain a single peak in the DOS, with power-law divergences. These higher-order divergences that appear in an NH system have a different origin than that of the higher-order VHS in Hermitian systems, where no saddle point merging is noted. Our results suggest NH interfaces to be promising avenues for exploring higher-order VHS.

In a conventional boson system, the ground state can either be an insulator or a superfluid (SF) due to the duality between particle number and phase. This paper reveals that the long-sought Bose metal (BM) state can be realized in an exactly solvable interacting bosonic model, i.e., the Bose-Hatsugai-Kohmoto (BHK) model, which acts as the nontrivial extension of Bose-Hubbard (BH) model. By tuning the parameters such as bandwidth $W$, chemical potential $\mu$, and interaction strength $U$, a BM state without any symmetry breaking can be accessed for a generic $W/U$ ratio, while a Mott insulator (MI) with integer boson density is observed at small $W/U$. The quantum phase transition between the MI and BM states belongs to the universality class of the Lifshitz transition, which is further confirmed by analyzing the momentum-distribution function, the Drude weight, and the SF weight. Additionally, our investigation at finite temperature reveals similarities between the BM state and the Fermi liquid, such as a linear-$T$ dependent heat capacity ($Cv\sim \gamma T$) and a saturated charge susceptibility (${\chi }_c\sim$ constant) as $T$ approaches zero. Comparing the BM state with the SF state in the standard BH model, we find that the key feature of the BM state is a compressible total wavefunction accompanied by an incompressible zero-momentum component. Given that the BM state prevails over the SF state at any finite $U$ in the BHK model, our paper suggests the possibility of realizing the BM state with on-site repulsion interactions in momentum space.

Rydberg physics, with its characteristic long-range interactions between single quantum states, was introduced into semiconductor physics with the observation of Rydberg excitons. To identify and understand spectroscopic signatures of those long-range interactions, we propose a quantitative simulation of an ensemble of Rydberg excitons. By reproducing typical pump-probe absorption spectra, we discuss the influence of the assumed van-der-Waals-type interaction potentials.

Our focus in this investigation lies in developing a noise model for a quantum thermal transistor model inspired by its electronic counterpart, with the primary aim of establishing a platform for constructing analogous models. Previous studies on coupled two-level systems-based thermal transistors were focused on their average energy exchange. In this paper, we shift our attention to exploring the stochastic behavior of such thermal transistors due to the disturbances caused to their environment, such as continuous measurements. In the literature, the master equation for the transistor model is derived using the reduced dynamics method. This way, it masks the study of the stochastic nature of the energy flows in the system due to disturbances to the environment. In this paper, we describe a quantum trajectory under measurement theory whose ensemble average unravels the master equation for a quantum thermal transistor. This allows us to analyze the fluctuations and noise levels in the transistor model with greater detail. Then, we produce a numerical solution for the transistor dynamics based on Euler-Maruyama approximation. This helps to establish a model for the thermal transistor, drawing parallels to the small-signal/noise model in an electronic transistor. We define two parameters, thermal conductance and output thermal resistance, to describe the small signal-like model for the thermal transistor. Through these investigations, we seek to gain insights that can help design advanced heat management devices at the quantum level.

The interplay between the non-Hermitian skin effect and the imaginary gap of lossy lattices results in the edge burst, a boundary-induced dynamical phenomenon in which an exceptionally large portion of particle loss occurs at the edge. Here, we find that this intriguing non-Hermitian dynamical phenomenon can be exactly mapped into the steady-state density distribution of a corresponding open quantum system. Consequently, the bulk-edge scaling relation of loss probability in the edge burst maps to that of steady-state density. Furthermore, we introduce a many-body open-system model in which the two-body loss generates an interaction-induced non-Hermitian skin effect. Using the positive-$P$ method, we demonstrate the validity of the scaling relation for steady-state correlators. These results provide a unique perspective on the interaction-induced many-body non-Hermitian skin effect. Our predictions are testable in state-of-the-art experimental platforms.

We propose a class of graphene-based moiré systems hosting flat bands on kagome and honeycomb moiré superlattices. These systems are formed by stacking a graphene layer on a 2D substrate with lattice constant approximately $\sqrt{3}$ times that of graphene. When the moiré potentials are induced by a 2D irreducible corepresentation in the substrate, the model shows a rich phase diagram of low-energy bands including eigenvalue fragile phases as well as kagome and honeycomb flat bands. Spin-orbit coupling in the substrate can lift symmetry-protected degeneracies and create spin Chern bands, and we observe spin Chern numbers up to three. We additionally propose a moiré system formed by stacking two graphene-like layers with similar lattice constants and Fermi energies but with Dirac Fermi velocities of opposite sign. This system exhibits multiple kagome and honeycomb flat bands simultaneously. Both models we propose resemble the hypermagic model of [Scheer et al., Phys. Rev. B 106, 115418 (2022)] and may provide ideal platforms for the realization of strongly correlated topological phases.