Superconductivity in non-centrosymmetric rhombohedral NbSe2

TL;DR

This study demonstrates that stacking non-centrosymmetric rhombohedral NbSe2 induces bulk superconductivity with unique properties, highlighting stacking engineering as a novel approach to modify superconductivity and nonlinear responses in layered materials.

Contribution

It reveals that stacking alone can induce bulk superconductivity in non-centrosymmetric NbSe2 and explores its unique properties and potential for nonlinear phenomena.

Findings

Superconductivity is a bulk property of 3R-NbSe2.

In-plane upper critical field exceeds Pauli limit, indicating strong Ising SOC.

Superconducting transition temperature is insensitive to layer number but sensitive to disorder.

Abstract

Crystal stacking offers a powerful yet underexplored route to engineer symmetry in layered superconductors. Here we report superconductivity in rhombohedral-stacked NbSe2 (3R-NbSe2), a non-centrosymmetric polytype in which global inversion symmetry is removed by stacking alone. Using comprehensive structural, transport, magnetic, and thermodynamic measurements, we establish superconductivity as a bulk property of the 3R phase and find that the in-plane upper critical field exceeds the Pauli paramagnetic limit, indicating the persistence of strong Ising-type spin-orbit coupling. Unlike the thickness-dependent superconductivity in centrosymmetric 2H-NbSe2, the superconducting transition temperature in 3R-NbSe2 shows little dependence on layer number but exhibits an unusually strong sensitivity to disorder. We further observe strongly enhanced nonlinear optical and electrical responses near the superconducting transition, consistent with stacking-induced inversion-symmetry breaking. Our results identify 3R-NbSe2 as a single-phase platform in which stacking engineering reshapes superconductivity and enables nonlinear transport phenomena in layered materials.