Field-Tunable Anisotropic Fulde-Ferrell Phase in NbSe$_2$/CrSiTe$_3$ Heterostructures

TL;DR

This study reports the experimental discovery of an anisotropic Fulde-Ferrell superconducting phase in NbSe2/CrSiTe3 heterostructures, enabled by symmetry breaking and spin-orbit coupling, revealing new ways to engineer quantum states in 2D materials.

Contribution

It provides the first experimental observation of an anisotropic FF phase in 2D heterostructures and explains its origin through symmetry analysis and mean field calculations.

Findings

Identification of a half-dome-shaped superconducting region in B-T diagram

Finite second harmonic resistance indicating anisotropic FF phase

Role of Rashba SOC and symmetry breaking in phase emergence

Abstract

The emergence of superconductivity in two-dimensional transition metal dichalcogenides with strong spin orbit coupling (SOC) has opened new avenues for exploring exotic superconducting states. Here, we report experimental observation of an anisotropic Fulde-Ferrell (FF) phase in few-layer NbSe$_2$/CrSiTe$_3$ heterostructures under in-plane magnetic fields. Through combined magnetoresistance and nonreciprocal transport measurements, we find that due to the couplings from the ferromagnetic CrSiTe$_3$, a half-dome-shaped region emerges in the magnetic field-temperature ($B$-$T$) diagram. Importantly, the half-dome-shaped region exhibits finite second harmonic resistance with in-plane anisotropy, indicating that the superconducting state is an anisotropic FF phase. Through a symmetry analysis combined with mean field calculations, we attribute the emergent anisotropic FF phase to the CrSiTe$_3$ layer induced Rashba SOC and three-fold rotational symmetry breaking. These results demonstrate that heterostructure stacking is a powerful tool for symmetry engineering in superconductors, which can advance the design of quantum devices in atomically thin superconducting materials.