Multi-Valley Superconductivity In Ion-Gated MoS2 Layers

TL;DR

This study demonstrates that multi-valley Fermi surfaces, involving multiple electron pockets, are crucial for superconductivity in ion-gated MoS2 layers, highlighting the importance of FS topology and Lifshitz transitions.

Contribution

It provides experimental evidence linking multi-valley Fermi surfaces to superconductivity in MoS2, emphasizing the role of Lifshitz transitions and multiple electron pockets.

Findings

Superconductivity correlates with the filling of Q/Q' valleys.

SC transition occurs after crossing spin-orbit split sub-bands.

Fermi surface connectivity promotes superconductivity.

Abstract

Layers of transition metal dichalcogenides (TMDs) combine the enhanced effects of correlations associated with the two-dimensional limit with electrostatic control over their phase transitions by means of an electric field. Several semiconducting TMDs, such as MoS$_2$, develop superconductivity (SC) at their surface when doped with an electrostatic field, but the mechanism is still debated. It is often assumed that Cooper pairs reside only in the two electron pockets at the K/K' points of the Brillouin Zone. However, experimental and theoretical results suggest that a multi-valley Fermi surface (FS) is associated with the SC state, involving 6 electron pockets at the Q/Q' points. Here, we perform low-temperature transport measurements in ion-gated MoS$_2$ flakes. We show that a fully multi-valley FS is associated with the SC onset. The Q/Q' valleys fill for doping$\gtrsim2\cdot10^{13}$cm$^{-2}$, and the SC transition does not appear until the Fermi level crosses both spin-orbit split sub-bands Q$_1$ and Q$_2$. The SC state is associated with the FS connectivity and promoted by a Lifshitz transition due to the simultaneous population of multiple electron pockets. This FS topology will serve as a guideline in the quest for new superconductors.