Covellite (CuS) is the first known natural mineral superconductor. Despite its simple chemical formula, covellite exhibits a rich crystal structure at the origin of several remarkable properties. The ionic arrangement in CuS crystals leads to a mixed valence of Cu and a second-order structural transition at 55 K. Despite the abundance of structural studies and theoretical reports on its electronic structure, there are scarce references on its experimental band structure. By means of angle-resolved photoemission spectroscopy (ARPES), we have probed the experimental electronic structure of covellite. We compare our results with the predictions of density-functional theory (DFT) calculations. Our experimental data are in remarkable agreement with the calculations, revealing subtle fingerprints of the structural phase transition, and confirming the quasi-2D nature of the electronic structure of CuS.

Recent studies have revealed that frustration-free models, expressed as sums of finite-range interactions or hoppings, exhibit several properties markedly different from those of frustrated models. In this work, we demonstrate that, by relaxing the finite-range condition to allow for exponentially decaying hoppings, one can build gapped frustration-free systems that realize Chern insulators as well as quasidegenerate ground states with finite-size splittings. Moreover, by permitting power-law decaying hoppings, we also construct a gapless band metal whose finite-size gap scales inversely with the system size $L$. These findings serve as an important step toward clarifying the general properties of frustration-free systems and those represented by tensor network states.

Supersymmetry provides a natural playground for the construction of dynamically constrained lattice fermion models. We here illustrate how supersymmetry can be used to construct a fermionic equivalent of the PXP model with an adjustable chemical potential. This model is closely related to the $\mathcal{N}=2$ supersymmetric $M_1$ model, inheriting its integrability. The supersymmetric algebra additionally implies that the dynamics exhibit periodic revivals for specific initial states, including the ${\mathbb{Z}}_2$-ordered (every second site occupied) product state. These dynamics are reminiscent to those of the PXP model, a paradigmatic effective model in the field of quantum many-body scars. We draw a further parallel by uncovering eigenstates obeying subthermal entanglement scaling at energies given by (plus or minus) square roots of integers and relate these to special eigenstates of the $M_1$ model. While we focus on a concrete model, our proposed approach is applicable to more general supersymmetric algebras, where it is expected to lead to nonergodic dynamics.

Ultrafast and nanoscale heat conduction demands a unified theoretical framework that rigorously bridges macroscopic transport equations with microscopic material properties derived from statistical physics. Existing empirical generalizations of Fourier's law often lack a solid microscopic foundation, failing to connect observed non-Fourier behavior with underlying atomic-scale mechanisms. In this work, we present a time-domain theory of transient heat conduction rooted in Zwanzig's statistical theory of irreversible processes. Central to this framework is the time-domain transport function $\overleftrightarrow{Z}\left(t\right)$ defined through equilibrium time-correlation functions of heat fluxes. This function generalizes the conventional concept of steady-state thermal conductivity, governing the transition of conduction dynamics from onset second sound type wave propagation at finite speeds to diffusion-dominated behavior across broad temporal and spatial scales. Unlike phonon hydrodynamic models that rely on mesoscopic constructs such as phonon drift velocity, our approach provides a quantitative and microscopic description of intrinsic memory effects in transient heat fluxes and applies universally to bulk materials at any temperature or length scale. By integrating atomistic-scale first-principles calculations with continuum-level macroscopic equations, this framework offers a robust foundation for numerical simulations of transient temperature fields. Furthermore, it facilitates the interpretation and design of transient thermal grating experiments using nanometer-scale heat sources and ultrafast laser systems in the extreme ultraviolet and x-ray wavelength ranges, advancing our understanding of heat dissipation dynamics.

Color centers in hexagonal boron nitride (hBN) have gained significant interest as single-photon emitters and spin qubits for applications in a wide range of quantum technologies. As the integration of these solid-state quantum emitters into electronic devices necessitates electrical control, it is essential to gain a deeper understanding of the mechanisms for charge control of these defect color centers in hBN/graphene heterostructures. In this article, we show that screening due to the encapsulation of hBN by graphene modifies the electrical levels of hBN, leading to charge transfer. Furthermore, we show that the charged defects have low-energy barriers for defect reorientation which can be overcome by moderate gate voltages. This study shows that accurate modeling of the charge state of the defect is necessary to be able to electrically control defects.

The interplay between topology and magnetism often triggers the exotic quantum phases. Here, we report an accessible scheme to engineer the robust ${\mathbb{Z}}_2$ topology by intrinsic magnetism, originating from the zigzag segment connecting two armchair segments with different width, in one-dimensional graphene nanoribbon heterojunctions. Our first-principle and model simulations reveal that the emergent spin polarization substantially modifies the dimerization between junction states, forming the special SSH mechanism depending on the magnetic configurations. Interestingly, the topological phase in magnetic state is only determined by the width of the narrow armchair segment, in sharp contrast with that in the normal state. In addition, the emergent magnetism increases the bulk energy band gap by an order of magnitude than that in the nonmagnetic state. We also discuss the $\mathbb{Z}$ topology of the junction states and the termination-dependent topological end states. Our results bring alternative way to tune the topology in graphene nanoribbon heterostructure, providing a alternative platform for future one-dimensional topological devices and molecular-scale spintronics.

I analyze electron transport through a Y junction formed by helical edge states of a two-dimensional topological insulator (2DTI), focusing on the strongly interacting regime. An experimentally motivated device geometry and a spin-conserving tunneling Hamiltonian are proposed. I compute the conductance tensor and show that, for specific tunneling phases and strong repulsive interactions ($g<1/2$), transport is governed by an intermediate renormalization group fixed point that interpolates between the weak- and strong-tunneling limits. These results extend previous studies of point-contact tunneling and demonstrate how interactions qualitatively modify the transport properties of multiterminal topological devices.

We theoretically investigate the anisotropic dispersion features of a two-dimensional electron gas at the (110) oriented ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interfaces, as revealed by scanning gate microscopy of electronic flow from a quantum point contact. The dispersion relation of the (110) ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface is characterized by a highly noncircular Fermi surface. Here, we develop an efficient tight-binding model for the electron gas at the interface. We show that the anisotropy of the Fermi surface causes both the direction of the electron flux from the quantum point contact and the periodicity of the self-interference conductance fringes to depend strongly on the orientation of the constriction relative to the crystal lattice. We show that the radially nonuniform distribution of the Fermi velocity on the Fermi surface results in skewing of electron trajectories when the quantum point contact gates are not aligned with the in-plane primitive vectors. We show that this effect results in the separation of electrons belonging to different orbitals for wide (110) ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ quantum wells.

The ability to generate light by nonlinear metasurfaces and shape its properties has made metasurfaces a promising platform for developing new types of nonlinear optical devices. Extending beyond the conventional two-dimensional metasurface has the potential to further enhance and control nonlinear processes in metamaterials. However, it still remains a challenge as it requires distinct and tailored phase matching schemes, different from those used in bulk nonlinear crystals. Here, we study theoretically and numerically the mechanism of second harmonic generation from a nonlinear bilayer metamaterial. We present a design approach that is based on adding nonlinear geometric phase to the layers, by a relative rotation of their meta-atoms orientation. We demonstrate how the nonlinear geometric phase affects the system through local and collective interactions, allows excitation of nontrivial solutions, and controls the second harmonic emission and directivity. It is found that the bilayer supports a bound mode with strongly enhanced dipole excitation, leading to a highly confined second harmonic field within the structure. The presented approach and results lay the foundation for designing efficient and tunable multilayer nonlinear metamaterials.

The Gutzwiller projection of fermionic wave functions is a well-established method for generating variational wave functions describing exotic states of matter, such as quantum spin liquids. We investigate the conditions under which a projected wave function constructed from fermionic partons can be rigorously shown to possess topological order. We demonstrate that these conditions can be precisely determined in the case of projected Majorana stabilizer codes. We then use matrix product states to study states that interpolate between two distinct Majorana fermion codes, one yielding a ${\mathbb{Z}}_2$ spin liquid and the other a trivial polarized state upon projection. While the free-fermion states are adiabatically connected, we find that the projected states undergo a phase transition detected by the topological entanglement entropy. Our work underscores the profound impact of the Gutzwiller projection and cautions against inferring properties of quantum spin liquids solely from their unprojected counterparts.

Nodal planes, two-dimensional symmetry-enforced band crossings, can carry a topological charge, similar to Weyl points. While the transport properties of Weyl points are well understood, those of nodal planes remain largely unexplored. These properties are influenced not only by the Berry curvature, but also by other quantum geometric quantities. In this work we study the quantum geometry, specifically the Berry curvature and quantum metric, and the linear optical conductivity of topological nodal planes. We introduce a low-energy model and investigate its low-frequency optical responses to determine the unique signatures of nodal planes. By comparing these findings to the optical response in a tight-binding model with a topological nodal plane, we observe consistent low-frequency behavior with a cubic power law. This paves the way for the experimental detection of nodal planes through optical conductivity measurements for which we suggest suitable materials, most promisingly the material group $X{\mathrm{Mo}}_3{\mathrm{S}}_3$ ($X=$ Rb, K, Cs).

We investigate the Cr electronic structure and excitations in CrSBr, a layered magnetic semiconductor, using a combination of resonant x-ray spectroscopic techniques. X-ray absorption spectroscopy and resonant inelastic x-ray scattering (RIXS) spectra collected at the Cr $L_{2,3}$ edges reveal significant linear dichroism, which arises from the distorted octahedral environment surrounding the ${\mathrm{Cr}}^{3+}$ ions. The origin of the bright excitons observed in this compound is examined through a comparison of the $d-d$ excitations identified in the RIXS spectra, the x-ray excited optical luminescence spectra, and previously reported optical spectroscopic and theoretical studies. To further understand these phenomena, we develop a multiplet model based on a crystal electric field approach that accounts for the local environment of Cr ions. This model successfully reproduces several experimental features, while also suggesting strong hybridization effects between Cr $3d$ orbitals and ligands that are not fully captured by the present framework. These findings advance our understanding of the electronic structure and excitonic behavior in CrSBr and provide a foundation for future in situ and operando studies of CrSBr-based devices for spintronic and optoelectronic applications.

We propose that phonons coupled to electrons play an important role in both the fundamental phenomenology of electron spin resonance as well as the interpretation of such measurements. By including spin-dependent electron-phonon interactions originating from spin-orbit coupling, we demonstrate that the $\mathrm{g}$-f actor acquires emergent temperature dependencies that are in excellent agreement with experimental observations. Moreover, we predict that at low temperatures, the $g$-factor will exhibit a nontrivial dependence on the magnetic field, indicating a dynamic property that has not been previously considered in electron-phonon systems. We further predict the influence of phonons to be negligible at very low and very high temperatures, with the former requiring experimental verification.

We study the influence of Hund's coupling on the nature of electronic correlations in ${\mathrm{Sr}}_2{\mathrm{CoO}}_4$ within dynamical mean-field theory. Our results suggest strong signatures of Hund's metal physics in this compound. The Co $3d$ states show a large orbital differentiation in the degree of correlations and mass enhancement. The imaginary-time correlation functions suggest the presence of spin-orbital separation and large local charge fluctuations in the system. A breakdown of the Fermi-liquid picture is observed at the lowest calculated temperature for various strengths of Hund's coupling, suggesting a Fermi-liquid coherence scale lower than $\sim 100$ K. Interestingly, a sudden emergence of a gapped state is noted for $e_g$ orbitals in its spectral density of states at $\sim 200$ K in the vicinity of the Fermi level. Among the Co $3d$ states, $3d_{z^2}$ and $3d_{x^2-y^2}$ foster enlarged correlations. This study conclusively identifies ${\mathrm{Sr}}_2{\mathrm{CoO}}_4$ as a single-layered $3d$ transition metal oxide to be classified as a Hund's metal.

Unraveling the behavior of the electrons in the copper-oxygen planes of cuprate superconductors remains a challenge. Here we examine the electronic charge redistribution among planar copper and oxygen orbitals and the charge gap using the Emery model in the normal state, solved with cellular dynamical mean-field theory at finite temperature. We quantify the charge redistribution as a function of the onsite Coulomb repulsion on the copper orbitals, the bare copper-oxygen energy difference, and the hole or electron doping. We find that the position relative to the metal to insulator boundary of the Zaanen-Sawatzky-Allen diagram determines the charge redistribution among copper and oxygen orbitals. For a fixed bare Cu-O energy difference, an increase in the Cu electron repulsion leads to a transfer of the electronic charge from Cu to O orbitals. For a fixed charge gap size of the undoped state, as the system evolves from a charge-transfer to a Mott-Hubbard regime, the electronic charge is transferred from Cu to O orbitals. Our findings posit the Coulomb repulsion and the bare charge-transfer energy as key drivers of the microscopic process of charge redistribution in the ${\mathrm{CuO}}_2$ plane. They quantify the anticorrelation between the charge gap size and oxygen hole content. They show that for fixed band-structure parameters, the charge gap and the charge redistribution between Cu and O orbitals provide a way to understand observed trends in cuprates.

Ternary chalcopyrites $(X\hspace{0.17em}=\hspace{0.17em}\mathrm{S},\mathrm{Se},\mathrm{Te})$ have attracted much attention due to their potential application in thermoelectrics and photovoltaics. Due to different fabricating techniques, experiment results on the carrier transport vary widely and the underlying mechanism of carrier scattering is still unclear. Based on the Boltzmann transport equation, we investigated the carrier transport properties of the ternary chalcopyrites by first-principles calculation plus Hubbard $U$. The calculation results of band gaps and the dielectric constants are close to the experiment results. It is found that the chalcopyrites have large electron mobilities, i.e., ${\mu }_e$ (300 K) of 266.7, 475.8, and $1319.7 {\mathrm{cm}}^2/\mathrm{Vs}$ for ${\mathrm{AgInS}}_2, {\mathrm{AgInSe}}_2$, and ${\mathrm{AgInTe}}_2$ respectively. In contrast, the hole mobility ${\mu }_h$(300 K) takes 18.2, 51.8, and $77.8 {\mathrm{cm}}^2/\mathrm{Vs}$ for three chalcopyrites, respectively. Calculation on the mode-resolved scattering rates reveals that the predominant carrier scattering is attributed to the $B_2^{\left(3\right)}$ mode, which relates to the longitudinal off-center motion of In relative to the tetrahedron ${\mathrm{InX}}_4$. The mobility decays as $\mu \propto T^{-\alpha }$, where $\alpha$ takes $0.89\sim 1.03$ for ${\mu }_e$ and $1.13\sim 1.88$ for ${\mu }_h$. The impurity scattering effect has also been studied by considering two kinds of substitutional defects, ${\mathrm{In}}_{\mathrm{Ag}}$ and ${\mathrm{Ag}}_{\mathrm{In}}$, which lead the chalcopyrites to be $n$ or $p$ type, accordingly. The impurities ${\mathrm{In}}_{\mathrm{Ag}}$ can suppress the electron mobilities to half values when the density reaches ${10}^{17}{\mathrm{cm}}^{-3}$ while the impurities ${\mathrm{Ag}}_{\mathrm{In}}$ only moderately decreases the hole mobilities. The distinct suppression of carrier mobilities owes to the difference of the Born effective charges for two kinds of impurities. Our calculation reveals that the predominant carrier scattering of $B_2^{\left(3\right)}$ can be attributed to its largest magnitude of electron-phonon matrix elements compared to other phonon modes.

In recent studies, it has been demonstrated that topological systems can host a variety of topological semimetal phases, including Weyl points, nodal lines, rings, chains, and nodal surfaces, offering diverse opportunities for exploring novel physical phenomena. However, previous studies mainly focused on exploring a single type of band degeneracy in topological systems. In this work, we demonstrate the coexistence of zero-dimensional Weyl points and one-dimensional nodal rings in the topological gyroelectric continuum media. Through rigorous theoretical analysis, we show a comprehensive depiction of topological phase diagrams of these band degenerates in the continuum media and give the critical conditions of the coexistence of Weyl points and nodal rings. Remarkably, the size of the nodal rings in three-dimensional momentum space that varies with the gyroelectric parameter ${\omega }_e$ and reveals the magnetic field strength can be regarded as the degree of freedom of control band degeneracies. The topologically protected Fermi arc surface states arise when the gyroelectric continuum media are in direct touch with the vacuum state owing to the bulk boundary correspondence. Moreover, a type of multichannel and reconfigurable photonic topological pathway is realized using the unidirectional Fermi arc surface states. This study establishes a flexible framework for examining the interactions between Weyl semimetals and nodal semimetals, paving the way for the development of innovative photonic topological devices with promising applications.

The interplay between structure distortion and lattice dynamics provides a compelling strategy to suppress phonon transport in thermoelectric materials. In this work, we explore the origin of highly anisotropic thermal conductivity in ${\mathrm{Sn}}_2{\mathrm{S}}_3$ through first-principles calculations combined with the Wigner transport equation (WTE). We find that the stereochemically active lone-pair electrons of ${\mathrm{Sn}}^{2+}$ pronounced local structural distortions, characterized by asymmetric Sn–S bond angles and weakened bonding configurations. These distortions activate rattling modes, which flatten vibrational branches, enhance phonon scattering, and reduce group velocities, particularly along the $x$ and $z$ directions. In contrast, the $y$ direction supports more coherent and dispersive phonon transport, leading to markedly higher thermal conductivity. Additionally, the influence of rattling extends to coherent phonon transport, yielding a complex frequency-dependent interplay between particlelike and wavelike heat conduction. Our results establish a direct link between lone-pair-induced anharmonicity and anisotropic phonon transport, offering a design framework for low-$\kappa$ materials beyond van der Waals or interlayer-driven strategies.

Interlayer exchange coupling (IEC) between two magnetic layers sandwiched by a nonmagnetic spacer layer plays a critical role in shaping the magnetic properties of such heterostructures. The quantum anomalous Hall (QAH) effect has been realized in a structure composed of two magnetically doped topological insulator (TI) layers separated by an undoped TI layer. In this work, we employ molecular beam epitaxy to synthesize a series of magnetic TI sandwiches with varying thicknesses of the middle undoped TI spacer layer. The well-quantized QAH effect is observed in all these samples, and the IEC modulates its critical behavior between the top and bottom magnetic TI layers. Near the plateau phase transition (PPT), thinner QAH samples exhibit a two-dimensional critical metal behavior with nearly temperature-independent longitudinal resistance. In contrast, thicker QAH samples behave as a three-dimensional insulator with reduced longitudinal resistance at higher temperatures. We employ a magnetic TI Hamiltonian with random magnetic domains to understand the IEC-induced critical-metal-to-insulator transition observed near QAH PPT.