Anomalous Photothermoelectric Transport Due to Anisotropic Energy Dispersion in WTe2

Abstract

© 2019 American Chemical Society. Band structures are vital in determining the electronic properties of materials. Recently, the two-dimensional (2D) semimetallic transition metal tellurides (WTe 2 and MoTe 2 ) have sparked broad research interest because of their elliptical or open Fermi surface, making distinct from the conventional 2D materials. In this study, we demonstrate a centrosymmetric photothermoelectric voltage distribution in WTe 2 nanoflakes, which has not been observed in common 2D materials such as graphene and MoS 2 . Our theoretical model shows the anomalous photothermoelectric effect arises from an anisotropic energy dispersion and micrometer-scale hot carrier diffusion length of WTe 2 . Further, our results are more consistent with the anisotropic tilt direction of energy dispersion being aligned to the b-axis rather than the a-axis of the WTe 2 crystal, which is consistent with the previous first-principle calculations as well as magneto-transport experiments. Our work shows the photothermoelectric current is strongly confined to the anisotropic direction of the energy dispersion in WTe 2 , which opens an avenue for interesting electro-optic applications such as electron beam collimation and electron lenses.