Asbjørn Drachmann

Enhancing transparent superconductor-semiconductor hybrids

Advances enabling future experiments in proximitized InAs(Sb) systems

Superconductor-semiconductor hybrids are studied, mainly due to the potential discovery of Majorana zero modes that could facilitate scalable quantum computers. Improving material quality and fabrication processes is believed necessary in order to realize Majorana zero mode applications. Important aspects of device processing include patterning and removal of superconducting material, which can lead to disorder/irregularities of the hybrid. This thesis investigates new techniques for superconductor patterning.

We demonstrate the prospects of using anodic oxidation on transparent superconductor-semiconductor hybrids, specifically on shallow InAs 2-dimensional electron gas (2DEG) heterostructures terminated with epitaxially grown Al. Partial oxidation of Al increases its superconducting critical temperature and critical magnetic fields. Compared to using a regular Al etch, a full Al oxidation passivates the underlying 2DEG, enhancing the carrier properties. The Quantum Hall effect is achieved one tesla below the highest achieved critical field of oxidized Al. Using a metal mask for lithography enables a lateral resolution <50 nm with anodic oxidation. The mask is used to construct a magnetic field resilient Josephson junction. The novel system of a disordered superconductor with transparent coupling to an underlying 2DEG, shows 1/B periodic magnetoresistivity oscillations both below and above the superconducting critical field. In particular, the oscillations below the critical field are studied as a function of magnetic field, temperature, and DC current. Lastly, suggestions for improvements of the anodic oxidation setup and for further material upgrades are elaborated.

Via zoom: https://ucph-ku.zoom.us/j/61631955239