A téma rövid leírása, a megoldandó legfontosabb feladatok felsorolása:

There is nowadays a vast interest in superconductor/semiconductor heterostrucrures both from fundamental research and application point of view. On the one hand, these structures could host novel states of matter, like topological superconductivity, which could enable the realization of quibits that are protected against perturbations. On the other hand they could be the building blocks of future ultra-fast superconducting electronics, where on of the current challenge is the interfacing of superconducting circuits with CMOS technology.  Moreover, tunable semiconducting Josephson junctions also have been incorporated in superconducting qubits, called gatemons, where the tunability of the qubit energy is achieved via electrostatic gating.

Gate tunable supercurrents can be realized in semiconducting Josephson junctions, where nowdays superconductors can be epitaxially grown on the semiconductors guaranteeing ideal superconducting properties. This was realized both for 2 dimensional electron gases and 1D nanowires also. Moreover a very recent and surprising discovery suggests that using intensive DC electric fields the supercurrent in metallic superconductors can also be tuned. Whereas the effect is clearly a game-changer in superconducting electronics, its physical origin is yet unclear.

During the PhD work the candidate will realize semiconducting/superconductor heterostructures and metallic superconducting structures using nanofabrication techniques. These systems will be studied using switching current measurements, current-phase relation and Shapiro measurements and will be integrated into larger superconducting circuits. The measurements will be done at ultra-low temperatures and in collaboration with several European universities.

 

Left: An Al coated InAs wire with local gates for supercurrent control. Right: Supercurrent gate control for different temperatures.

 

A jelentkezővel szemben támasztott elvárások:

Knowledge of solid state physics, motivation for experimental work, English knowledge, basic programming and measurement automation experience