PhD Project

Competition between Coulomb blockade and multiple Andreev reflection

Objectives: The goal of the project is to reveal the nature of particular superconducting charge transport processes, called multiple Andreev reflections (MAR) by setting them into competition with Coulomb blockade. Simultaneously I will explore the concept of Coulomb blockade on a microscopic level. Transport in Coulomb blockade-driven systems like single-electron transistors (SETs) requires energy proportional to the square of the charge of the carriers, while the necessary energy for MAR processes decreases with increasing number of carriers. I will use electron beam lithography and shadow evaporation to fabricate aluminum-based SETs comprising one oxide-tunnel junction and one tunable contact using a break-junction. The design will be such that the charging energy will be in the same order as the superconducting energy. MAR contributions will be in situ tuned by the break junction while Coulomb blockade is controlled by a side gate. I will study electron transport at very low temperature in the superconducting S and the normal N states to disentangle contributions originating from Coulomb blockade and from MAR. I will address the question which parameter determines the appearance of Coulomb blockade in the coherent situation, when the island is in the S state (SSS SET) as well, and the non-coherent situation with an N island (SNS-SET). The sample preparation needed to maintain the superconducting state in the junctions while having a normal island will be performed in collaboration with Early Stage Researcher 14 at RAITH (Germany). I will regularly discuss scientific questions and results with Early Stage Researchers 1, 2, 3 (CNRS, France) and 7 (ETH Switzerland), who work on related topics and I will profit from the expertise in mesoscopic superconductivity and Coulomb blockade from CNRS and ETH.