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We consider a planar superconducting–normal metal junction with both inelastic and spin-flip scattering processes present. In the diffusive limit, we use a one-dimensional formulation of the Usadel equation to compute the self-consistent energy dependence of the single-particle density of states as a function of distance from the interface on both the superconducting and metallic sides for various spatial profiles of a pair-breaking spin-flip term. The pair-breaking processes fill in the superconducting gap at zero energy, which is reflected in the zero-bias tunneling conductance in scanning tunneling microscopy/spectroscopy experiments, in the vicinity of the junction. We also investigate the impact of having a partially transparent interface at the junction. We compare our findings with the observed exponential rise in the zero-bias conductance at the 1H step edge in recent experiments on 4Hb-TaS2 [A. K. Nayak et al., Nat. Phys. 17, 1413 (2021)]. 

Circularly polarized lattice vibrations carry angular momentum and lead to magnetic responses in applied magnetic fields or when resonantly driven with ultrashort laser pulses. Recent measurements have found responses that are orders of magnitude larger than those calculated in prior theoretical studies. Here, we present a microscopic model for the effective magnetic moments of chiral phonons in magnetic materials that can reproduce the experimentally measured magnitudes and that allows us to make quantitative predictions for materials with giant magnetic responses using microscopic parameters. Our model is based on orbit-lattice couplings that hybridize optical phonons with orbital electronic transitions. First, we test our model by applying it to 4⁢𝑓 rare-earth halide paramagnets, which are known to exhibit a giant phonon Zeeman effect. Next, we predict that this effect can also occur for optical phonons in 3⁢𝑑 transition-metal oxide magnets. We show that the nature of low-energy excitations involved in phonon hybridization is remarkably different than that of rare-earth systems. The temperature trend of phonon magnetic moment in 𝑑-orbital magnets also reveals valuable insights about the magnetic ground state and the unique interplay of spin, orbital, and lattice degree of freedom. In both cases, we find that chiral phonons can carry giant effective magnetic moments of the order of a Bohr magneton, orders of magnitude larger than previous predictions. 

We theoretically study the influence of quenched outside disturbances in an intermediately long-time limit. We consider localized imperfections, uniform fields, noise, and couplings to an environment within a unified framework using a prototypical but idealized interacting quantum device—the Kitaev honeycomb model. As a measure of stability we study the Uhlmann fidelity of quantum states after a quench. To treat the unperturbed dynamics as a free-fermion model without neglecting evolution of states between flux sectors, we push the flux degree of freedom into the perturbation. For noisy quenches, both gapped and gapless systems exhibit a universal form for the long-time fidelity, 𝐶⁢𝑒−𝛼⁢𝑡⁢𝑡−𝛽 where the values of 𝐶, 𝛼, and 𝛽 depend on physical parameters such as system size and disturbance strength. Finally, we show that selective filling of the spinon Brillouin zone can be used to greatly increase the fidelity over the ground-state value. Our work provides estimates for the intermediate long-time stability of a quantum device, offering engineering guidelines for quantum devices in quench design and system size. 

We theoretically study first- and second-order optical responses in a transition-metal dichalcogenide monolayer with distinct trivial, nodal, and time-reversal invariant topological superconducting (TRITOPS) phases. We show that the second-order dc response, also known as the photogalvanic response, contains signatures for differentiating these phases while the first-order optical response does not. We find that the high-frequency photogalvanic response is insensitive to the phase of the system, while the low-frequency response exhibits features distinguishing the three phases. At zero doping, corresponding to an electron filling in which the Fermi level lies at nodal points, there are opposite sign zero-frequency divergences in the response when approaching the nodal phase boundaries from the trivial and the TRITOPS phases. In the trivial phase, both the high-frequency and low-frequency response of the system are negative, but in the TRITOPS phase the low-frequency response becomes positive while the high-frequency response remains negative. Furthermore, since phase transitions are controlled by the Rashba spin-orbit coupling and the ratio of intraorbital and interorbital paring amplitudes, our results not only help distinguish the phases but they can also provide an estimate of the pairing amplitudes based on the photogalvanic response of the system. 

We theoretically study the conditions under which an intrinsic spin Nernst effect–a transverse spin current induced by an applied temperature gradient–can occur in a canted-antiferromagnet insulator, such as LaFeO3 and other materials of the same family. The spin Nernst effect may provide a microscopic mechanism for an experimentally observed anomalous thermovoltage in LaFeO3⁢/Pt heterostructures, where spin is transferred across the insulator/metal interface when a temperature gradient is applied to LaFeO3 parallel to the interface [W. Lin et al., Nat. Phys. 18, 800 (2022)]. We find that LaFeO3 exhibits an intrinsic spin Nernst effect when inversion symmetry is broken on the axes parallel to both the applied temperature gradient and the direction of spin transport, which can result in a spin injection across the insulator/metal interface. Our paper provides a general derivation of a symmetry-breaking-induced spin Nernst effect, which may open a path to engineering a finite spin Nernst effect in systems where it would otherwise not arise. 

Abstract Symmetry-protected topological crystalline insulators (TCIs) have primarily been characterized by their gapless boundary states. However, in time-reversal- ($${{{{{{{\mathcal{T}}}}}}}}$$ $T$-) invariant (helical) 3D TCIs—termed higher-order TCIs (HOTIs)—the boundary signatures can manifest as a sample-dependent network of 1D hinge states. We here introduce nested spin-resolved Wilson loops and layer constructions as tools to characterize the intrinsic bulk topological properties of spinful 3D insulators. We discover that helical HOTIs realize one of three spin-resolved phases with distinct responses that are quantitatively robust to large deformations of the bulk spin-orbital texture: 3D quantum spin Hall insulators (QSHIs), “spin-Weyl” semimetals, and$${{{{{{{\mathcal{T}}}}}}}}$$ $T$-doubled axion insulator (T-DAXI) states with nontrivial partial axion angles indicative of a 3D spin-magnetoelectric bulk response and half-quantized 2D TI surface states originating from a partial parity anomaly. Using ab-initio calculations, we demonstrate thatβ-MoTe₂realizes a spin-Weyl state and thatα-BiBr hosts both 3D QSHI and T-DAXI regimes.