Evidence for two-dimensional Ising superconductivity in gated MoS ₂

TLDR

The Zeeman effect, normally detrimental to superconductivity, can instead protect superconductivity in gated MoS₂ because intrinsic spin–orbit coupling from broken in‑plane inversion symmetry generates an effective Zeeman field of up to ~100 T that pins electron spins out‑of‑plane and shields the superconducting state from in‑plane magnetic fields. Magnetotransport measurements on ionic‑gated MoS₂ transistors, where different carrier dopings create distinct superconducting states, reveal spin‑protected superconductivity with an in‑plane critical field Bc2 that far exceeds the Pauli paramagnetic limit. The gating‑enhanced Bc2 is more than an order of magnitude larger than in bulk phases, providing the first experimental evidence of an Ising superconductor in which the pairing electrons’ spins are strongly pinned by the effective Zeeman field.

Abstract

The Zeeman effect, which is usually considered to be detrimental to superconductivity, can surprisingly protect the superconducting states created by gating a layered transition metal dichalcogenide. This effective Zeeman field, which is originated from intrinsic spin orbit coupling induced by breaking in-plane inversion symmetry, can reach nearly a hundred Tesla in magnitude. It strongly pins the spin orientation of the electrons to the out-of-plane directions and protects the superconductivity from being destroyed by an in-plane external magnetic field. In magnetotransport experiments of ionic-gate MoS$_{2}$ transistors, where gating prepares individual superconducting state with different carrier doping, we indeed observe a spin- protected superconductivity by measuring an in-plane critical field $\textit{B}$$_{c2}$ far beyond the Pauli paramagnetic limit. The gating-enhanced $\textit{B}$$_{c2}$ is more than an order of magnitude larger compared to the bulk superconducting phases where the effective Zeeman field is weakened by interlayer coupling. Our study gives the first experimental evidence of an Ising superconductor, in which spins of the pairing electrons are strongly pinned by an effective Zeeman field.