Twisted oxide membrane interface by local atomic registry design

TL;DR

This study demonstrates the design and fabrication of twisted oxide membranes with controlled moiré structures, revealing lattice-dependent charge states and predicting emergent electronic phases driven by moiré phenomena.

Contribution

We introduced a method to create and analyze moiré structures in complex oxide membranes, uncovering charge disproportionation and predicting new electronic phases at the twisted interface.

Findings

Ordered charge states at the moiré interface

Lattice-dependent charge disproportionation observed

Prediction of flat bands leading to new electronic phases

Abstract

Interplay of lattice, orbital, and charge degrees of freedom in complex oxide materials has hosted a plethora of exotic quantum phases and physical properties. Recent advances in synthesis of freestanding complex oxide membranes and twisted heterostructures assembled from membranes provide new opportunities for discovery using moir\'e design with local lattice control. To this end, we designed moir\'e crystals at the coincidence site lattice condition, providing commensurate structure within the moir\'e supercell arising from the multi-atom complex oxide unit cell. We fabricated such twisted bilayers from freestanding SrTiO3 membranes and used depth sectioning-based TEM methods to discover ordered charge states at the moir\'e interface. By selectively imaging SrTiO3 atomic planes at different depths through the bilayer, we clearly resolved the moir\'e periodic structure at the twisted interface and found that it exhibits lattice-dependent charge disproportionation in the local atomic registry within the moir\'e supercell. Our density-functional modelling of the twisted oxide interface predicts that these moir\'e phenomena are accompanied by the emergence of a two-dimensional flat band that can drive new electronic phases. Our work provides a novel guideline for controlling moir\'e periodicity in twisted oxides and opens pathways to exploit the new functionalities via moir\'e lattice-driven charge-orbital correlation.