Local probing of superconductivity at oxide interfaces with atomic force microscopy

Abstract

Abstract Superconductivity in strontium titanate has remained enigmatic for over 50 years. The LaAlO 3 /SrTiO 3 (LAO/STO) heterointerface enables systematic dimensional confinement, from two-dimensional electron gas to quasi-one-dimensional nanostructures, providing unprecedented access to this quantum state. While transport measurements in patterned devices reveal puzzling phenomena, including width-independent critical currents and anomalous pairing, suggesting one-dimensional behavior, direct local probes for the patterned interface and its superconducting response have remained lacking. Here, we use ultra-low temperature non-contact atomic force microscopy with dissipation spectroscopy and Kelvin probe force microscopy to locally probe signatures of superconductivity in patterned LAO/STO devices. Spatially resolved energy dissipation measurements reveal signatures of superconductivity with some features confined to edge channels of order ≈200 nm in width. Dissipation spectra exhibit a characteristic nonlinear bias dependence that provides a local diagnostic of superconductivity consistent with the intermediate carrier density near the superconducting dome, which persists up to the critical field. These results demonstrate the ability of atomic force microscopy to probe superconductivity in patterned LAO/STO structures, potentially addressing fundamental, longstanding questions about quantum confinement and transport anomalies in these correlated nanostructures.