One-dimensional Kronig-Penney superlattices at the LaAlO$_3$/SrTiO$_3$ interface

TL;DR

This paper demonstrates the creation of one-dimensional superlattices at the LaAlO3/SrTiO3 interface using c-AFM lithography, revealing new electronic subbands, tunable conductance, and stable electron pairing, advancing quantum material design and simulation.

Contribution

It introduces a method to impose artificial superlattice potentials on 1D electron waveguides, enabling control over subband structure and electron pairing in solid-state systems.

Findings

Imposed superlattice potentials create new subbands with tunable fractional conductance.

The lowest conductance plateau indicates stable spin-singlet electron pairs up to high magnetic fields.

Engineered spin-orbit interaction enhances electron pairing in the superlattice.

Abstract

The paradigm of electrons interacting with a periodic lattice potential is central to solid-state physics. Semiconductor heterostructures and ultracold neutral atomic lattices capture many of the essential properties of 1D electronic systems. However, fully one-dimensional superlattices are highly challenging to fabricate in the solid state due to the inherently small length scales involved. Conductive atomic-force microscope (c-AFM) lithography has recently been demonstrated to create ballistic few-mode electron waveguides with highly quantized conductance and strongly attractive electron-electron interactions. Here we show that artificial Kronig-Penney-like superlattice potentials can be imposed on such waveguides, introducing a new superlattice spacing that can be made comparable to the mean separation between electrons. The imposed superlattice potential "fractures" the electronic subbands into a manifold of new subbands with magnetically-tunable fractional conductance (in units of $e^2/h$). The lowest $G=2e^2/h$ plateau, associated with ballistic transport of spin-singlet electron pairs, is stable against de-pairing up to the highest magnetic fields explored ($|B|=16$ T). A 1D model of the system suggests that an engineered spin-orbit interaction in the superlattice contributes to the enhanced pairing observed in the devices. These findings represent an important advance in the ability to design new families of quantum materials with emergent properties, and mark a milestone in the development of a solid-state 1D quantum simulation platform.