Giant Seebeck effect across the field-induced metal-insulator transition of InAs

TL;DR

This study demonstrates a giant Seebeck effect in InAs during a magnetic-field-induced metal-insulator transition, highlighting phonon drag as the primary mechanism behind the large thermoelectric response.

Contribution

It reveals a significant enhancement of the Seebeck coefficient linked to a magnetic-field-driven transition, emphasizing the role of phonon drag in low-density quantum limit systems.

Findings

Seebeck coefficient increases 200-fold near transition

Large thermoelectric response attributed to phonon drag

Transition caused by magnetic field reducing carrier density

Abstract

Lightly doped III-V semiconductor InAs is a dilute metal, which can be pushed beyond its extreme quantum limit upon the application of a modest magnetic field. In this regime, a Mott-Anderson metal-insulator transition, triggered by the magnetic field, leads to a depletion of carrier concentration by more than one order of magnitude. Here, we show that this transition is accompanied by a two-hundred-fold enhancement of the Seebeck coefficient which becomes as large as 11.3mV.K$^{-1}\approx 130\frac{k_B}{e}$ at T=8K and B=29T. We find that the magnitude of this signal depends on sample dimensions and conclude that it is caused by phonon drag, resulting from a large difference between the scattering time of phonons (which are almost ballistic) and electrons (which are almost localized in the insulating state). Our results reveal a path to distinguish between possible sources of large thermoelectric response in other low density systems pushed beyond the quantum limit.