Two-Fold Anisotropic Superconductivity in Bilayer T$_d$-MoTe$_2$

TL;DR

This study investigates the anisotropic superconductivity in bilayer T$_d$-MoTe$_2$, revealing a two-fold symmetry in critical fields and identifying tilted Ising spin-orbit coupling as the key mechanism behind its enhanced superconducting properties.

Contribution

It provides the first detailed experimental analysis of the angular dependence of superconductivity in bilayer T$_d$-MoTe$_2$ and links it to tilted Ising spin-orbit coupling through first-principles calculations.

Findings

Superconductivity exhibits two-fold symmetry with maxima along the b-axis.

Spin-orbit coupling strength reaches up to 16.4 meV.

Tilted Ising spin-orbit coupling is identified as the dominant mechanism.

Abstract

Noncentrosymmetric 2D superconductors with large spin-orbit coupling offer an opportunity to explore superconducting behaviors far beyond the Pauli limit. One such superconductor, few-layer T$_d$-MoTe$_2$, has large upper critical fields that can exceed the Pauli limit by up to 600%. However, the mechanisms governing this enhancement are still under debate, with theory pointing towards either spin-orbit parity coupling or tilted Ising spin-orbit coupling. Moreover, ferroelectricity concomitant with superconductivity has been recently observed in the bilayer, where strong changes to superconductivity can be observed throughout the ferroelectric transition pathway. Here, we report the superconducting behavior of bilayer T$_d$-MoTe$ _2$ under an in-plane magnetic field, while systematically varying magnetic field angle and out-of-plane electric field strength. We find that superconductivity in bilayer MoTe$_2$ exhibits a two-fold symmetry with an upper critical field maxima occurring along the b-axis and minima along the a-axis. The two-fold rotational symmetry remains robust throughout the entire superconducting region and ferroelectric hysteresis loop. Our experimental observations of the spin-orbit coupling strength (up to 16.4 meV) agree with the spin texture and spin splitting from first-principles calculations, indicating that tilted Ising spin-orbit coupling is the dominant underlying mechanism.