Tunable thermoelectricity in monolayers of MoS2 and other group-VI dichalcogenides

M Tahir,U Schwingenschlögl

doi:10.1088/1367-2630/16/11/115003

M Tahir, U Schwingenschlögl

Open Access

https://doi.org/10.1088/1367-2630/16/11/115003

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Abstract

We study the thermoelectric properties of monolayers of MoS2 and other group-VI dichalcogenides under circularly polarized off-resonant light. Analytical expressions are derived for the Berry phase mediated magnetic moment, orbital magnetization, as well as thermal and Nernst conductivities. Tuning of the band gap by off-resonant light enhances the spin splitting in both the valence and conduction bands and, thus, leads to a dramatic improvement of the spin and valley thermoelectric properties.

Highlights

Being the first truly two dimensional material [1], graphene has attracted remarkable attention, both due to its exotic transport behavior and technological applications in various fields [2]
Fundamental problems restrict its applicability, in particular the negligible band gap and weak spin orbit coupling (SOC). These limitations could be overcome by monolayer MoS2, which is interesting for generation nanoelectronics [3,4,5,6,7]
MoS2 combines the honeycomb structure of graphene with a large intrinsic direct band gap of 2Δ = 1.66 eV and a large SOC of λ = 74 meV, providing mass to the Dirac fermions [8,9,10]

Summary

Introduction

Being the first truly two dimensional material [1], graphene has attracted remarkable attention, both due to its exotic transport behavior and technological applications in various fields [2]. Of particular interest is the tuning of the spin and valley thermoelectric properties of MoS2 and other group-VI dichalcogenides, where a temperature gradient gives rise to transverse spin/ valley accumulation and spin/valley current In graphene this is difficult to realize due to the negligible band gap and weak SOC. In the present work we quantify the Berry phase mediated thermoelectric properties of MoS2 and other group-VI dichalcogenides by deriving analytical expressions for the key thermoelectric quantities in the presence of circularly polarized off-resonant light Gap opening by such light has been predicted for graphene and for the surface states of topological insulators [22], and has been confirmed experimentally for the latter [23]. We demonstrate in the following that by off-resonant light large spin and valley thermoelectric effects can be achieved

Model formulation

Orbital magnetic moment and temperature dependent orbital magnetization

Conclusion