Tunable topological Nernst effect in 2D transition metal dichalcogenides

TL;DR

This paper demonstrates that the valley Nernst effect in 2D transition metal dichalcogenides can be significantly enhanced and tuned via Rashba spin-orbit coupling and external gating, offering new avenues for caloritronics.

Contribution

It reveals that Rashba SOC and external gating can greatly amplify and control the valley Nernst signal in TMDs, highlighting a tunable topological thermoelectric effect.

Findings

Rashba SOC enhances the Nernst signal by 1-2 orders of magnitude.

The Nernst signal is dominated by anomalous geometrical contributions.

External gating and magnetic coupling can tune and amplify the Nernst response.

Abstract

Two dimensional semiconducting transition metal dichalcogenides (TMDs) exhibit an intrinsic Ising spin orbit coupling (SOC) along with a valley contrasting Berry curvature, which can generate a purely anomalous spin and valley Nernst signal driven by a thermal gradient. We show that a small Bychkov-Rashba coupling, which is present in gated TMDs, can enhance the valley Nernst signal by at least 1-2 orders of magnitude. We find that the Nernst signal in these materials is dominated by the anomalous geometrical contribution, and the conventional contribution is much weaker. Importantly, the Nernst signal is also highly tunable by external gating. Although the total Nernst signal vanishes due to time reversal (TR) symmetry, a small magnetic coupling lifts the valley degeneracy and generates an amplified Nernst response. Additionally, we also discuss the Nernst response of bilayer TMDs, and show a similar enhancement and modulation of the Nernst signal due to Rashba SOC. Our predictions are highly pertinent to ongoing experimental studies in TMDs. The generated large anomalous Nernst signal can directly probe the presence of a large Berry curvature in these materials, and may serve as a promising tunable platform for caloritronics applications.