Kaitai Xiao | Searcharxiv

arXiv2026

Multi-Knob Switchable Chiral Superconductivity Quartet in Rhombohedral Graphene

Chiral superconductors break orbital time-reversal symmetry and may host topological quasiparticles with non-Abelian statistics. In rhombohedral graphene, superconductivity develops from a spin-valley-polarized quarter-metal (QM) parent state and features unique magnetic hysteresis of resistance that indicates orbital time-reversal-symmetry-breaking. Exploring and controlling the full spin-valley flavors of such superconductivity could enable novel superconducting and topological devices, but have remained unexplored. Here we report transport measurements on rhombohedral hexalayer graphene (R6G), which reveal a new superconducting state (SCH) that is induced by an out-of-plane magnetic field, in addition to chiral superconductivity (CSC) similar to those observed in thinner layers. This SCH state emerges above 0.8 T, persists up to 1.6 T and can be switched on/off by magnetic field $H_\perp$, carrier density $n$, and gate displacement field $D$. Quantum oscillations and anomalous Hall measurements show that SCH stems from a field-induced quarter-metal (QM$'$) parent phase, which carries orbital magnetization opposite to that of the zero-field QM. Across the full $(n, D, H_\perp)$ parameter space, superconductivity can be realized from all four spin-valley isospin flavors, establishing a switchable chiral-superconductor quartet in R6G. We interpret the parent-state switching as arising from competition between a Kane-Mele-like spin-valley splitting and magnetic-field coupling to spin-valley-dependent magnetic moments. Our work establishes rhombohedral graphene as a multi-knob platform for different isospin-polarized superconductivities, which enables programmable superconducting networks with possible Majorana modes along domain walls.

cond-mat.supr-con↗

arXiv2025

Nonreciprocal Transport with Quantum Geometric Origin in Layered Hybrid Perovskite

Quantum geometry quantifies how the electron wavefunction evolves distinctly from conventional transport theory. In noncentrosymmetric materials, nonreciprocal transport with quantum geometric origin remains prominent with localized charge independent of vanished group velocity. The discovery of such nonreciprocal and nonlinear responses was realized by recent advances in two-dimensional materials. As a promising candidate, the electronic structure and symmetry of layered hybrid perovskites can be deliberately designed and manipulated by incorporating selected organic ligands. Despite the observation of exotic photogalvanic effects and chiral optical effects, the underlying mechanism how these nonlinear responses are enabled in the multi-quantum well structures remained unclear. Here we demonstrated the quantum geometric origin for interlayer spontaneous photocurrent in (PEA)2PbI4. Contrary to assumptions that charge transport across the 2D planes is limited, we observed a spontaneous photocurrent along this crystalline orientation. Theoretical analysis using a tight-binding model identifies shift current as the microscopic origin. This quantum geometric effect is enabled by ionic displacements from centrosymmetric coordinates and enhanced by multiband transition high-density bands of the layered hybrid crystal. We anticipate that such unique low-dimensional systems with structure can provide fertile ground for discovering novel optoelectronic functionalities.

cond-mat.mtrl-sci↗