Probing and Tuning the Spin Textures of the K and Q Valleys in Few‐Layer MoS2

Abstract

The strong spin–orbit coupling along with broken inversion symmetry in transition metal dichalcogenides (TMDs) results in spin polarized valleys, which are the origins of many interesting properties such as Ising superconductivity, circular dichroism, valley Hall effect, etc. Herein, it is shown that encapsulating few‐layer MoS2 between hexagonal boron nitride (h‐BN) and gating the electrical contacts by ionic liquid pronounce Shubnikov–de Haas (SdH) oscillations in magnetoresistance. Notably, the SdH oscillations remain unchanged in tilted magnetic fields, demonstrating that the spins of the Q/Q′ valleys are firmly locked to the out‐of‐plane direction; therefore, Zeeman energy is insensitive to the in‐plane magnetic field. Ionic liquid gating induces superconductivity on the surface of unencapsulated MoS2. The spins of Cooper pairs are strongly pinned to the out‐of‐plane direction by the effective Zeeman field, hence are protected from being realigned by an in‐plane magnetic field, namely, Ising protection. As a result, superconductivity persists in an in‐plane magnetic field up to 14 T, in which Tc only decreases by ≈0.3 K from Tc0 as ≈7 K. By applying back gate, the strength of Ising protection can be effectively tuned, where an increase in 70% is observed when back gate changes from +90 to −90 V.