Giant enhancement of cryogenic thermopower by polar structural instability in the pressurized semimetal MoTe2

TL;DR

This study reveals that polar structural instability in pressurized MoTe2 significantly enhances cryogenic thermopower, resulting in a giant thermoelectric power factor due to electron-phonon interactions.

Contribution

It demonstrates a large thermopower enhancement near the polar structural transition in pressurized MoTe2, highlighting the role of phonon softening and electron-phonon scattering.

Findings

Thermopower reaches 60 μV/K at 25 K under 0.75 GPa pressure.

Giant thermoelectric power factor of 300 μW/K^2·cm achieved.

Polar structural transition influences electron-phonon interactions.

Abstract

We found that a high mobility semimetal 1T'-MoTe2 shows a significant pressure-dependent change in the cryogenic thermopower in the vicinity of the critical pressure, where the polar structural transition disappears. With the application of a high pressure of 0.75 GPa, while the resistivity becomes as low as 10 {\mu}{\Omega}cm, thermopower reached the maximum value of 60 {\mu}VK-1 at 25 K, leading to a giant thermoelectric power factor of 300 {\mu}WK-2cm-1. Based on semiquantitative analyses, the origin of this behavior is discussed in terms of inelastic electron-phonon scattering enhanced by the softening of zone center phonon modes associated with the polar structural instability.