High-critical-field superconducting heterostructures using anodic oxidation

In-situ growth of Al on top of shallow InAs 2DEG heterostructures gives close to perfect proximity effect [1-2]. The transparent super/semi interface combined with customizable 2DEG lithography hold promise to many interesting applications, e.g. topological quantum computation [3-4].
When the aluminum is chemically etched the underlying InAs is degraded by surface impurities. [2]
Instead of etching the aluminum, here we show that controllably oxidizing the Al through anodic oxidation (AO) gives up to a factor 2 increase in InAs mobility and Quantum Hall effect emerges before 3 Tesla.
We will also show how AO can be used to controllably thin down Al, thus increasing its superconducting properties [2,5-6], obtaining an in-plane critical field > 6 T and a perpendicular critical field > 3T on a mesoscopic structure.
Besides enhancing superconducting properties of established devices, this technique paves the way to new research topics, eg. Quantum Hall edge states proximitized by the surface Al with close to unity transparency.

[1] M. Kjærgaard et al. Nature commun. 12841
[2] J. Shabani et al. Phys. Rev. B 93, 159908
[3] F. Nichele et al. Phys. Rev. Lett. 119, 136803
[4] A. Fornieri et al. arXiv:1809.03037
[5] Y. Ivry et al. Phys. Rev. B 90, 214515
[6] P. Tedrow et al. Phys. Rev. B 25, 171