Abstract
The thermoelectric response of 80 nm-thick strained HgTe films of a three-dimensional topological insulator (3D TI) has been studied experimentally. An ambipolar thermopower is observed where the Fermi energy moves from conducting to the valence bulk band. The comparison between theory and experiment shows that the thermopower is mostly due to the phonon drag contribution. In the region where the 2D Dirac electrons coexist with bulk hole states, the Seebeck coefficient is modified due to 2D electron–3D hole scattering.
Highlights
A three-dimensional topological insulator (3D TI) has a gapless surface state inside the bulk band-gap [1,2,3,4]
We found that thermopower in a 3DTI is due to phonon drag, which is similar to a 2D semimetal system in 20 nm HgTe wells
While our experiment offers an interesting outlook on thermopower in this region, more experimental and theoretical work is required to understand the behavior of the friction between 2D electron and 3D holes in a 3D topological insulator
Summary
A three-dimensional topological insulator (3D TI) has a gapless surface state inside the bulk band-gap [1,2,3,4]. The surface state energy spectrum has the form of a Dirac cone, which holds massless particles. The spin of surface Dirac electrons is locked perpendicular to the wave vector k in the 2D plane, which leads to the suppression of the electron scattering on impurities. The wide strain HgTe films are among of the best host. The thermoelectric measurements can probe the sign of the charge carriers and the transport mechanisms and are widely used to obtain complementary information about electron transport in metals and semiconductors. The value of the thermoelectric coefficient strongly depends on the energy spectrum and the mechanism of the time relaxation. An important relationship exists between the diffusive thermopower
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