Ning Hao

The intrinsic superconducting diode effect (SDE) is distinguished from the Josephson diode effect by its manifestation of nonreciprocal critical current phenomena within a monolithic superconductor, typically linked to finite-momentum Cooper pairing. The long-standing assumption that SDE requires cobreaking of time-reversal and inversion symmetries proves to be necessary but not sufficient. In this work, we propose an algebraic diagnostic criterion for intrinsic SDE, expressed as two inequalities evaluated directly from the bare Hamiltonian. This criterion further reveals a graph-theoretic construction for nonreciprocal models, offering design principles that extend beyond superconductivity.

Spin-charge interconversion is a central functionality of spintronics. Using three effective k ⋅ p models, we reveal how spin-charge interconversion is governed by the spin texture of Rashba-type bands, distinguishing systems with opposite-chirality spin-split Fermi contours (conventional Rashba bands) from those with same-chirality contours (unconventional Rashba bands). High-throughput screening of trigonal MX ₂ monolayers, combined with first-principles and Wannier-based tight-binding calculations, reveals a wide diversity of Fermi-surface spin textures that our models capture near the Brillouin-zone center. We show that the current-induced nonequilibrium spin polarization and relevant spin current are controlled by the group velocity, density of states, and spin texture, leading to pronounced Fermi-level sensitivity. At zeros of nonequilibrium spin polarization, i.e., the energies at which the current-induced nonequilibrium spin polarization vanishes, multiband cancellation suppresses the net Edelstein response and strongly reduces the spin-charge interconversion efficiency, even in the presence of strong spin-orbit coupling. Our results expose the rich landscape of spin textures in noncentrosymmetric two-dimensional (2D) trigonal materials and the subtle, highly nontrivial nature of spin-charge interconversion in realistic systems. The complexity can be explicitly attributed to the interplay of spin-orbit coupling, band-structure details (e.g., multiband effects and anisotropy), and scattering processes, which together govern the efficiency and sign of spin-charge interconversion.

Symmetry breaking underlies various nonreciprocal transport phenomena. A well-known example is the semiconductor p − n junction diode, a cornerstone of modern electronics. Its superconducting counterpart—the superconducting diode effect (SDE)—has recently attracted intense interest due to its potential in ultra-low-power superconducting circuits. While most SDEs reported so far involve either explicit or spontaneous breaking of time-reversal symmetry (TRS), a comprehensive theoretical framework remains elusive. Moreover, a general mechanism enabling TRS-preserving SDEs with minimal dependence on material or device architecture has yet to be established. Here, we report polarity-tunable SDEs without breaking TRS, realized in superconducting n − n , p − n , and p − p homojunctions defined via local protonic gates in multilayer NbSe 2 . The local gates induce partial proton intercalation, generating a built-in proton concentration gradient across the transition zone between the gated and ungated regions—closely resembling the depletion layer in conventional semiconductor diodes. We find that the observed SDE arises from electric-field-driven variation of the proton concentration gradient in the transition region, which asymmetrically modulates the critical current: suppressing it in one direction and enhancing it in the other. This local-gate-driven, TRS-preserving mechanism offers a general and scalable strategy for realizing nonreciprocal superconducting transport. Our findings establish a material-agnostic platform for SDEs, broadly applicable across two-dimensional (2D) superconductors.

Higher-order topological superconductors host Majorana zero modes localized at corners or hinges, providing a promising route toward scalable and controllable Majorana networks without vortices or magnetic flux. Here we propose a symmetry-enforced higher-order topological superconductivity based on antiferromagnetic topological insulators, specifically realized in MnXPb$_2$ (X = Se, Te)-Pb heterostructure. We show that the intrinsic boundary dichotomy-gapless Dirac states protected by an effective time-reversal symmetry on antiferromagnetic edges and magnetic gaps on ferromagnetic edges-naturally generates Majorana corner modes as mass domain walls. Superconducting proximity converts the antiferromagnetic edges into one-dimensional topological superconductors, and the intersections between superconducting and magnetic edges bind Majorana zero modes as mass domain walls. Combining first-principles calculations with a calibrated effective boundary theory, we demonstrate robust corner localization and purely electrical control of Majorana fusion and braiding in a triangular geometry. Our results establish MnXPb$_2$ as experimentally promising platform for electrically programmable Majorana networks in two dimensions.