Local probing of superconductivity at oxide interfaces with atomic force microscopy

TL;DR

This study employs ultralow-temperature atomic force microscopy to locally detect and characterize superconductivity at patterned LaAlO3/SrTiO3 interfaces, revealing edge-confined superconducting regions and nonlinear bias signatures.

Contribution

It introduces atomic force microscopy as a local diagnostic tool for superconductivity in oxide nanostructures, enabling direct spatial and spectroscopic analysis.

Findings

Superconducting signatures are confined to edge channels approximately 200 nm wide.

Dissipation spectra show a nonlinear bias dependence characteristic of superconductivity.

Superconductivity persists up to the critical magnetic field in patterned oxide interfaces.

Abstract

Superconductivity in strontium titanate has remained enigmatic for more than 50 years. The LaAlO$_3$/SrTiO$_3$ (LAO/STO) heterointerface enables systematic dimensional confinement, from a two-dimensional electron gas to quasi-one-dimensional nanostructures, providing access to this quantum state. Transport measurements in patterned devices reveal puzzling phenomena, including width-independent critical currents and anomalous pairing suggestive of one-dimensional behavior, but direct local probes of the patterned interface and its superconducting response have been lacking. Here we use ultralow-temperature non-contact atomic force microscopy, dissipation spectroscopy, and Kelvin probe force microscopy to locally probe signatures of superconductivity in patterned LAO/STO devices. Spatially resolved energy-dissipation measurements reveal superconducting signatures, with features confined in some devices to edge channels approximately 200 nm wide. Dissipation spectra exhibit a characteristic nonlinear bias dependence that provides a local diagnostic of superconductivity, consistent with the intermediate carrier-density regime near the superconducting dome, and persisting up to the critical field. These results establish atomic force microscopy as a local probe of superconductivity in patterned LAO/STO structures and provide a route to addressing longstanding questions about quantum confinement and transport anomalies in correlated oxide nanostructures.