Suppression of Superconductivity and Electrostatic Side Gate Tuning in High Mobility SrTiO$_3$ Surface Electron Gas

TL;DR

This study fabricates high-mobility SrTiO$_3$ 2DEGs, finds suppression of superconductivity, and demonstrates electrostatic side gate tuning, revealing new insights into oxide quantum device potential.

Contribution

It introduces a method to create high-mobility SrTiO$_3$ 2DEGs with suppressed superconductivity and explores electrostatic gating effects, advancing oxide electronics.

Findings

High electron mobility up to 7400 cm$^2$/V$ ext{s}$ achieved.

Superconductivity was suppressed down to 10 mK in these 2DEGs.

Electrostatic side gate modulation improves with larger gate-to-channel separation.

Abstract

We report on the fabrication and characterization of patterned high-mobility two-dimensional electron gases (2DEG) formed on SrTiO$_3$ (STO) substrate surfaces by hydrogen plasma exposure. The resulting devices consistently showed high electron mobilities up to 7400 cm$^2$/V$\cdot$s. A large range of electron density was systematically explored by controlled aging of the sample between cooldowns, including the expected range for the STO 2DEG superconducting dome. No superconducting transition was observed down to the base temperature of approximately 10 mK. This suggests suppression of superconductivity in high mobility quasi-two-dimensional SrTiO$_3$ electron gas, likely linked to vertical confinement and electronic orbital rearrangement. We systematically explored electrostatic gate modulation in this 2DEG system and its scaling with electron density and side gate geometry. In contrast with our initial expectation, we observed an improvement of achievable total modulation for larger side gate to channel separation. At low electron density, stochastic channel pinch-off events were observed, creating quasi-ballistic constrictions with irregular conductance quantization. This epitaxy-free and high mobility oxide material platform offers a promising new route towards patterning quantum devices.