When electrons meet ferroelastic domain walls in Strontium Titanate

TL;DR

This paper reviews how electrons interact with ferroelastic domain walls in SrTiO$_3$, revealing complex phenomena like polarity emergence, quantum fluctuations, and their effects on electronic transport.

Contribution

It synthesizes recent experimental and theoretical findings on the interplay between nanoscale polar order, quantum effects, and strain fields at ferroelastic domain walls in SrTiO$_3$.

Findings

Emergence of polarity at domain walls influences electron behavior.

Quantum fluctuations induce glass-like electron relaxations.

Strain fields modulate charge carrier dynamics.

Abstract

Strontium titanate (SrTiO$_3$), famously described by Nobel laureate K. A. M\"uller as the "drosophila of solid-state physics", has been extensively investigated over the last seventy five years for its intricate coupling of structural, electronic, and dielectric properties and continues to serve as a foundational platform for advancing oxide electronics. In its pristine form, SrTiO$_3$ exhibits quantum paraelectric behavior below 35 K and undergoes an antiferrodistortive phase transition near 105 K. This transition generates ferroelastic twin domains separated by a dense network of domain walls, which function as nanoscale structural defects with far-reaching consequences. While the static influence of ferroelastic domain walls on carrier transport in electron-doped SrTiO$_3$ is well established, recent experimental results show that the emergence of polarity at these walls, combined with strain fields and inherent quantum fluctuations, induces correlated dynamical phenomena such as glass-like relaxations of electrons and memory effects. In this review, we highlight these recent advances, focusing on the subtle interplay between the emergence of nanoscale polar order, quantum fluctuations, and long-range strain fields. We propose that understanding charge carrier dynamics in the background of these complex ferroelastic domain wall landscapes offers a new paradigm for exploring electronic transport in the presence of local polar order and quantum fluctuations, with broad implications for correlated oxides.