Metal-Insulator Transition of the LaAlO3-SrTiO3 Interface Electron System

TL;DR

This paper investigates the metal-insulator transition at the LaAlO3-SrTiO3 interface, showing how carrier density tuning via electric gating induces a transition with distinct electrical behaviors and critical thresholds.

Contribution

It demonstrates the electric-field-controlled metal-insulator transition in LaAlO3-SrTiO3 interfaces, revealing unique critical behavior and conductivity dependence not seen in semiconductor 2D systems.

Findings

Divergence of differential resistance at critical carrier density

Conductivity exhibits a threshold electric field below n_c

Conductivity follows a (n - n_c)/n_c dependence

Abstract

We report on a metal-insulator transition in the LaAlO3-SrTiO3 interface electron system, of which the carrier density is tuned by an electric gate field. Below a critical carrier density n_c ranging from 0.5-1.5 * 10^13/cm^2, LaAlO3-SrTiO3 interfaces, forming drain-source channels in field-effect devices are non-ohmic. The differential resistance at zero channel bias diverges within a 2% variation of the carrier density. Above n_c, the conductivity of the ohmic channels has a metal-like temperature dependence, while below n_c conductivity sets in only above a threshold electric field. For a given thickness of the LaAlO3 layer, the conductivity follows a sigma_0 ~(n - n_c)/n_c characteristic. The metal-insulator transition is found to be distinct from that of the semiconductor 2D systems.