Electric-field-induced pyroelectric order and localization of the confined electrons in LaAlO3/SrTiO3 heterostructures

TL;DR

This study reveals that electric fields induce pyroelectric order in SrTiO3, which strongly influences electron localization at LaAlO3/SrTiO3 interfaces, affecting their electronic and superconducting properties at low temperatures.

Contribution

It demonstrates that pyroelectric phase transitions in SrTiO3 under electric fields significantly impact electron localization and the quantum phase transition in LaAlO3/SrTiO3 heterostructures.

Findings

Electron localization is enhanced by pyroelectric order at low temperatures.

Pyroelectric and charge localization phenomena exhibit similar hysteresis loops.

Pyroelectric order influences the suppression of superconductivity under electric fields.

Abstract

With infrared ellipsometry, x-ray diffraction, and electric transport measurements we investigated the electric-field-effect on the confined electrons at the LaAlO3/SrTiO3 interface. We obtained evidence that the localization of the electrons at low temperature and negative gate voltage is induced, or at least strongly enhanced, by a pyroelectric phase transition in SrTiO3 which strongly reduces the lattice polarizability and the subsequent Coulomb screening. In particular, we show that the charge localisation and the polar order of SrTiO3 both develop below about 50 K and exhibit similar, unipolar hysteresis loops as a function of the gate voltage. Our findings suggest that the pyroelectric order also plays an important role in the quantum phase transition at very low temperatures where superconductivity is suppressed by an electric field.