Anomalous conductivity, Hall factor, magnetoresistance, and thermopower of accumulation layer in $\text{SrTiO}_3$

TL;DR

This paper investigates the unusual low-temperature electrical properties of the electron accumulation layer in SrTiO3, revealing how nonlinear dielectric response causes divergent conductivity contributions and results in anomalously large mobility and related effects.

Contribution

It demonstrates how the nonlinear dielectric response leads to a slowly decaying electron density tail, causing divergence in conductivity and related transport phenomena, with implications for understanding SrTiO3 surface layers.

Findings

Electron density decays as 1/x^{12/7} from the surface.

Conductivity divergence is truncated by sample width, bulk scattering, or dielectric crossover.

Anomalously large mobility and related effects depend on truncation physics.

Abstract

We study the low temperature conductivity of the electron accumulation layer induced by the very strong electric field at the surface of $\text{SrTiO}_3$ sample. Due to the strongly nonlinear lattice dielectric response, the three-dimensional density of electrons $n(x)$ in such a layer decays with the distance from the surface $x$ very slowly as $n(x) \propto 1/x^{12/7}$. We show that when the mobility is limited by the surface scattering the contribution of such a tail to the conductivity diverges at large $x$ because of growing time electrons need to reach the surface. We explore truncation of this divergence by the finite sample width, by the bulk scattering rate, or by the crossover to the bulk linear dielectric response with the dielectric constant $\kappa$. As a result we arrive at the anomalously large mobility, which depends not only on the rate of the surface scattering, but also on the physics of truncation. Similar anomalous behavior is found for the Hall factor, the magnetoresistance, and the thermopower.