Patterning of superconducting two-dimensional electron gases based on AlO$_x$/KTaO$_3$(111) interfaces

TL;DR

This paper introduces three patterning techniques for superconducting AlO$_x$/KTaO$_3$(111) 2DEG devices, enabling nanoscale device fabrication and carrier density tuning, advancing research into exotic electromagnetic effects in oxide interfaces.

Contribution

It presents novel patterning methods for AlO$_x$/KTaO$_3$(111) 2DEGs, facilitating device fabrication and exploration of their properties at the nanoscale.

Findings

Devices exhibit superconducting transitions from 1.3 K to 1.78 K.

Patterning causes limited degradation of superconducting properties.

Techniques enable large range of device dimensions for nanoscale exploration.

Abstract

The versatility of properties displayed by two-dimensional electron gases (2DEGs) at oxide interfaces has fostered intense research in hope of achieving exotic electromagnetic effects in confined systems. Of particular interest is the recently discovered superconducting state appearing in (111)-oriented KTaO$_3$ interfaces, with a critical temperature $T_c \approx 2$ K, almost ten times higher than that of SrTiO$_3$-based 2DEGs. Just as in SrTiO$_3$-based 2DEGs, fabricating devices in this new system is a technical challenge due to the fragility of the 2DEG and the propensity of bulk KTaO$_3$ to become conducting outside the devices upon adventitious oxygen vacancy doping. Here, we present three different techniques for patterning Hall bars in AlO$_x$/KTaO$_3$~(111) heterostructures. The devices show superconducting transitions ranging from 1.3 K to 1.78 K, with limited degradation from the unpatterned thin film, and enable an efficient tuning of the carrier density by electric field effect. The array of techniques allows for the definition of channels with a large range of dimensions for the design of various kinds of devices to explore the properties of this system down to the nanoscale.