Mechanical detection of sub-band mobilities of two-dimensional electron gas on reduced SrTiO$_3$(001) surface

TL;DR

This study introduces a non-invasive AFM-based method to measure sub-band mobilities and charge dynamics in 2DEG on reduced SrTiO₃, revealing bias and magnetic field effects.

Contribution

It combines atomic force microscopy and spectroscopy to quantify energy losses and carrier mobilities in 2DEG, advancing understanding of oxide electronics.

Findings

Confirmed 2DEG formation via Rydberg-like states.

Revealed bias-dependent dissipation peaks linked to charge redistribution.

Extracted carrier mobilities using Kohler's rule under magnetic fields.

Abstract

The two-dimensional electron gas (2DEG) in reduced strontium titanate offers a versatile platform for oxide electronics, yet its dissipation mechanisms under field driven charge fluctuations remain poorly understood. Here, we combine low-temperature atomic force microscopy with scanning tunnelling spectroscopy to probe the force and dissipation responses of a mechanical oscillator interacting with the STO 2DEG. The observation of Rydberg like image potential states by tunnelling experiments confirm the 2DEG formation, while dissipation spectroscopy reveals bias-dependent peaks linked to local electrostatic gating and charge redistribution within the 2DEG energy sub-bands. These features are quantitatively explained by variations in quantum capacitance as carrier density is tuned by electric fields. Under magnetic fields, dissipation peaks obey the Kohler's rule, allowing extraction of carrier mobilities in each sub-band. Our results establish a non-invasive AFM - based methodology for quantifying energy losses in quantum oxides, providing new insights into charge dynamics relevant for spintronic applications.