Quasiparticle and Nonquasiparticle Transport in Doped Quantum Paraelectrics

TL;DR

This paper investigates charge transport in doped quantum paraelectrics, explaining the observed T^2 resistivity behavior through a model involving electron-phonon interactions and a non-quasiparticle regime at higher temperatures.

Contribution

It introduces a model of electrons coupled to soft TO phonons via a two-phonon mechanism, explaining the T^2 resistivity and non-quasiparticle behavior in doped quantum paraelectrics.

Findings

Resistivity scales as T^2 above the soft-mode frequency.

T^2 scattering rate is independent of carrier density.

The model fits experimental data well.

Abstract

Charge transport in doped quantum paralectrics (QPs) presents a number of puzzles, including a pronounced $T^2$ regime in the resistivity. We analyze charge transport in a QP within a model of electrons coupled to a soft transverse optical (TO) mode via a two-phonon mechanism. For $T$ above the soft-mode frequency but below some characteristic scale ($E_0$), the resistivity scales with the occupation number of phonons squared, i.e., as $T^2$. The $T^2$ scattering rate does not depend on the carrier number density and is not affected by a crossover between degenerate and non-degenerate regimes, in agreement with the experiment. Temperatures higher than $E_0$ correspond to a non-quasiparticle regime, which we analyze by mapping the Dyson equation onto a problem of supersymmetric quantum mechanics. The combination of scattering by two TO phonons and by a longitudinal optical mode explains the data quite well.