Phonon drag thermopower and weak localization

TL;DR

This paper investigates how weak localization affects phonon drag thermopower and conductivity in low mobility 2D electron gases, revealing that thermopower is less sensitive to localization effects than conductivity, supported by experiments and theory.

Contribution

It provides new experimental data and a theoretical model explaining the insensitivity of phonon drag thermopower to weak localization in 2D and 3D semiconductors.

Findings

Thermopower changes due to weak localization are much smaller than conductivity changes.

Experimental results show minimal impact of weak localization on thermopower in low mobility 2D gases.

A theoretical framework explains the physical reasons for the insensitivity of $S^g$ to weak localization.

Abstract

Previous experimental work on a two-dimensional (2D) electron gas in a Si-on-sapphire device led to the conclusion that both conductivity and phonon drag thermopower $S^g$ are affected to the same relative extent by weak localization. The present paper presents further experimental and theoretical results on these transport coefficients for two very low mobility 2D electron gases in $\delta-$doped GaAs/Ga$_x$Al$_{1-x}$As quantum wells. The experiments were carried out in the temperature range 3-7K where phonon drag dominates the thermopower and, contrary to the previous work, the changes observed in the thermopower due to weak localization were found to be an order of magnitude less than those in the conductivity. A theoretical framework for phonon drag thermopower in 2D and 3D semiconductors is presented which accounts for this insensitivity of $S^g$ to weak localization. It also provides transparent physical explanations of many previous experimental and theoretical results.