We investigate the effects of interfacial spin-orbit coupling (ISOC) on superconductors, focusing on its impact on electronic transport and spin-charge conversion. Using a symmetry-based nonlinear sigma model, we derive effective boundary conditions for the Usadel and Maxwell equations that account for the spin-galvanic effect, spin relaxation, and spin precession. This approach allows for the analysis of various interfaces without relying on specific microscopic models. We apply these boundary conditions to derive ISOC-induced terms in the Ginzburg-Landau functional, which is then used to compute the critical temperature of superconducting films with ISOC subjected to an external magnetic field. Our findings show that, contrary to a recent prediction, the critical temperature of a film cannot be enhanced by an external magnetic field. Additionally, we demonstrate that the combination of ISOC and an external magnetic field leads to a superconducting-diode effect. Its efficiency strongly depends on the interplay between the spin-galvanic and the spin relaxation terms. Our results provide a framework for understanding ISOC in superconducting systems and highlight the potential for optimizing diode efficiency through careful interface engineering.

The imposition of crystalline symmetries is known to lead to a rich variety of insulating and superconducting topological phases. These include higher-order topological phases and obstructed atomic limits with and without filling anomalies. We here comprehensively classify such topological crystalline phases (TCPs) with mirror, twofold rotation, and inversion symmetries in the presence of disorder that preserves the crystalline symmetry on average. We find that the inclusion of disorder leads to a simplification of the classification in comparison to the clean case. We also find that, while clean TCPs evade a general bulk-boundary principle, disordered TCPs admit a complete bulk-boundary correspondence, according to which (bulk) topological phases are topologically equivalent if and only if they have the same anomalous boundary states and filling anomaly. We corroborate the stability of disordered TCPs by way of field-theoretic, numerical, and symmetry-based analyses in various case studies. While the boundary signatures of most disordered TCPs are similar to their clean counterparts, the addition of disorder to certain mirror-symmetric TCPs results in novel higher-order statistical topological phases, in which zero-energy hinge states have critical wave-function statistics, while remaining protected from Anderson localization.

Identifying and studying the underlying two-electron interactions that give rise to emergent phenomena is a key step in developing a holistic understanding of quantum materials. This step is hindered by the lack of an experiment that can directly interrogate the interactions and the specific quasiparticles involved in the interaction simultaneously. We introduce correlation-ARPES as an experimental method that overcomes this difficulty and directly measures the interactions between specific, chosen quasiparticles by measuring the correlations between two electrons photoemitted from the same pulse (but not the same photon). We illustrate how this technique can extract the underlying interactions and demonstrate this with an example of phonon-mediated electron-electron interactions, such as those that give rise to charge density waves through the Kohn anomaly mechanism.

We investigate the two-leg Hubbard model with diagonal hopping to explore the interplay between geometrical frustration and strong electron-electron interactions. Using the Density Matrix Renormalization Group (DMRG) method, we demonstrate the emergence of a topological Haldane phase, which results explicitly from the complementary effects of diagonal hopping-induced frustration and strong on-site Coulomb repulsion. The topological phase transition from a trivial insulator to the nontrivial Haldane phase is characterized by significant changes in magnetic properties, edge correlations, and the appearance of a nonzero string order parameter. Furthermore, we confirm the topological nature of this phase through a detailed analysis of the spin gap and entanglement spectrum, demonstrating clear signatures of symmetry-protected topological order.

The planar Hall effect (PHE) is a powerful tool for characterizing Weyl semimetals (WSMs). Here, we investigate the PHE in general anisotropic WSMs under strong magnetic fields. We analytically derive the Landau levels (LLs) and their wavefunctions using the Bogoliubov transformation, where the tilt vector, the anisotropic axis of the Fermi velocity, and the magnetic field can be oriented in arbitrary directions. Notably, as a result of the interaction with the magnetic field and the anisotropy of the Fermi velocity, the component of the tilt vector perpendicular to the magnetic field can induce a tilt in the LLs parallel to the magnetic field. Our analytical results show that the LLs do not collapse in type-I WSMs but must collapse in type-II WSMs when the magnetic field is perpendicular to the tilt vector. More importantly, we demonstrate that the magnetotransport signal of the LL collapse, which manifests as a significant enhancement and quantum oscillations in the longitudinal and planar Hall conductivities simultaneously, can be used to identify the phase transition from type-I to type-II WSMs.

We investigate the impact of order parameter fluctuations on magnetoelectric effects in metallic systems using classical Monte Carlo simulations. We focus on a chiral quadrupole order in a distorted kagomé network in a model incorporating conduction electrons and classical orbital moments. The ordered orbital moments break mirror symmetry and couple with the conduction electrons, leading to a current-induced magnetization driven by the orbital order. Our findings reveal that order-parameter fluctuations significantly affect the current-induced magnetization, strongly suppressing the response over a broad temperature range below the transition temperature. Additionally, we analyze the influence of Fermi surface properties and associated matrix elements on this phenomenon. Our results highlight the crucial role of fluctuation effects, demonstrating a qualitatively distinct temperature dependence of the current-induced magnetization compared to that of the order parameter itself.

We study the Aharonov-Bohm flux-induced magnetic response of a disordered non-Hermitian ring. The disorder is introduced through an on-site quasiperiodic potential described by the Aubry-André-Harper (AAH) model, incorporating a complex phase that renders the model non-Hermitian. Our findings reveal that this form of non-Hermiticity enhances the persistent current without requiring hopping dimerization. We explore both noninteracting and interacting scenarios. In the former, we examine spinless fermions within the tight-binding (TB) framework, while in the latter, we consider spinful fermions with Hubbard interactions. We employ the density-matrix renormalization group (DMRG) method to find the ground state energy of the Hubbard Hamiltonian for larger system sizes. The non-Hermitian phase induces both real and imaginary components of the current. We thoroughly analyze the energy eigenspectrum, ground state energy, and persistent current in both real and imaginary spaces for various system parameters. Our primary goal is to investigate the combined effects of non-Hermiticity and disorder strength on persistent currents. We find an enhancement in both the real and imaginary components of the persistent current with increasing disorder strength and non-Hermiticity, up to a critical value. Furthermore, we observe an enhancement in the persistent current in the presence of Hubbard correlations. Our findings may provide a new route to get nontrivial characteristics in persistent currents for a special type of non-Hermitian systems.

We present the spectral analysis of a one-dimensional Hubbard model with a parabolic potential, using a real-space cluster perturbation theory (CPT) designed to study spatially inhomogeneous electron systems with strong correlation. It is a natural extension of the conventional CPT to inhomogeneous cases by computing local Green's functions while averaging over multiple cluster boundaries. We find that the local density of states at each site mirrors that of a homogeneous system with the same local filling. This insight provides a perspective on spectral evolution in inhomogeneous systems used to scan the occupancy-dependent features of the homogeneous system, making this setup a practical one-shot spectroscopy tool for ultracold atoms in harmonic traps.

We study the interplay between topology and electron-electron interactions in the moiré ${\mathrm{MoTe}}_2/{\mathrm{WSe}}_2$ heterobilayer. In our analysis we apply an effective two-band model with complex hoppings that incorporates the Ising-type spin-orbit coupling and lead to a nontrivial topology after the application of perpendicular electric field (displacement field). The model is supplemented by onsite and intersite Coulomb repulsion terms and treated by both Hartree-Fock and Gutzwiller methods. According to our analysis, for the case of one hole per moiré unit cell, the system undergoes two phase transitions with increasing displacement field. The first one is from an in-plane ${120}^{\circ }$ antiferromagnetic charge transfer insulator to a topological insulator. At the second transition, the system becomes topologically trivial and an out-of-plane ferrimagnetic metallic phase becomes stable. In the topological region a spontaneous spin-polarization appears and the holes are distributed in both layers. Additionally, we analyze the influence of the intersite Coulomb repulsion terms on the appearance of the topological phase as well as on the formation of the charge density wave state. We discuss the obtained results in the context of available experimental data.

The topological Dirac nodal-line semimetal CaAgAs has received significant research attention due to its unique physical properties. Moreover, CaAgAs offers an ideal platform to study the linear and second-order nonlinear optical properties of nodal-line semimetals owing to the tunable radius of the nodal ring in the $\mathrm{CaAg}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ alloy and the structural centrosymmetric symmetry breaking. In this work, we study the linear and second-order nonlinear optical properties of CaAgX $(X=\mathrm{As} \text{and} \mathrm{P})$ and their alloys by density functional theory and a low-energy effective Hamiltonian. The peak values of the imaginary part of the dielectric function and the plateaus of optical conductivity in the low-frequency range are tunable by the radius of the nodal ring in the $\mathrm{CaAg}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ alloy with different concentrations of P doping. The peak value of the second-harmonic generation for both materials is around 400 pm/V, while the peak value of the shift current for both materials is around 20 $\mu \mathrm{A}/{\mathrm{V}}^2$. The linear band of topological node-line semimetal can inhibit second-harmonic generation within a low-frequency range due to the linear band dispersion near the Fermi level. The shift current of $\mathrm{CaAg}X$ $(X=\mathrm{As} \text{and} \mathrm{P})$ remains small in the low-frequency range, which is attributed to the low joint density of states value in this range. Our research results indicate that $\mathrm{CaAg}X$ holds potential for applications in nonlinear optics and tunable linear electro-optic devices.

The $g$-tensor formalism is a powerful method for describing the electrical driving of semiconductor spin qubits. However, up to now, this technique has only been applied to the simplest qubit dynamics, resonant monochromatic driving by a single gate. Here, we study the description of (i) monochromatic driving using two driving gates and bichromatic driving via (ii) one or (iii) two gates. Assuming a general Hamiltonian with qubit states well separated from excited orbital states, we find that when (i) two driving gates are used for monochromatic driving or (ii) a single one for bichromatic, the $g$-tensor formalism successfully captures the leading-order dynamics. We express the Rabi frequency and the Bloch-Siegert shift using the $g$-tensor and its first and second derivatives with respect to the gate voltage. However, when (iii) bichromatic driving is realized using two distinct driving gates, we see a breakdown of $g$-tensor formalism: The Rabi frequency cannot be expressed using the $g$-tensor and its derivatives. We find that beyond the $g$-tensor and its derivatives, three additional parameters are needed to capture the dynamics. We demonstrate our general results by assuming an electron (hole) confined in a circular quantum dot, subjected to Rashba spin-orbit interaction.

We present a detailed study of hole-doped Ge/SiGe multiple quantum wells as a promising material platform for mid-infrared photonics. The heterostructures were grown on SiGe virtual substrates using low-energy plasma-enhanced chemical vapor deposition. Structural and compositional analyses via atom probe tomography and x-ray diffraction were employed to assess the crystal quality and retrieve the compositional profiles. The optical response of the samples, in the 4–12-µm wavelength range, was investigated as a function of the temperature and complementary Hall-effect measurements were performed providing insights into the temperature evolution of the electrical transport properties. In addition, a well-established tight-binding model was used to reproduce and interpret the experimental results starting from the calculated valence band structure.

We present an exact solution for effective polaron-polaron interactions between heavy impurities, mediated by a sea of noninteracting light fermions in the quantum Hall regime with highly degenerate Landau levels. For weak attraction between impurities and fermions, where only the manifold of lowest Landau levels is relevant, we obtain an analytical expression of mediated polaron-polaron interactions. Remarkably, polaron interactions are exactly zero when fermions in the lowest Landau levels outnumber heavy impurities. For strong attraction, different manifolds of higher Landau levels come into play and we derive a set of equations that can be used to numerically solve the mediated polaron interaction potential. We find that the potential vanishes when the distance $R$ between impurities is larger than the magnetic length, but strongly diverges at short range following a Coulomb form $-1/R$. Our exact results of polaron-polaron interactions might be examined in cold-atom setups, where a system of Fermi polarons in the quantum Hall regime is realized with a synthetic gauge field or under fast rotation. Our predictions could also be useful to understand the effective interaction between exciton-polarons in electron-doped semiconductors under strong magnetic field.

Using a combined dynamical mean-field theory and Hartree (DMFT $+$ H) calculation we study the transport and optical properties of the eight-band heavy-fermion model for twisted bilayer graphene (TBG) in the normal state. We find resistive states around integer fillings which resemble the ones observed in transport experiments. From a Drude fitting of the low-frequency optical conductivity, we extract a very strongly doping-dependent Drude weight and scattering rate, resetting at the integers. For most dopings, particularly above the integers, the Drude scattering rate is high but notably smaller than that of the local electrons. This highlights the important role of itinerant electrons in the transport properties, despite their limited spectral weight on the flat bands. At far-infrared frequencies, the optical conductivity exhibits cascades characterized by highly asymmetric resets of the intensity and oscillations in the interband peak frequencies.