Seminar by Thomas Aref – University of Copenhagen

Seminar by Thomas Aref

Single Electron Turnstiles and NIS Coolers: Andreev tunneling and Phonon Heating Effects

Superconductor-Insulator-Normal-Insulator-Superconductor (SINIS) tunnel junctions can function both as single electron turnstiles and as electronic coolers. As a turnstile, the goal is to allow electrons through one at a time as a gate is swept. This directly relates current (via frequency of the signal applied to the gate) to the fundamental constant of electron charge, a key goal in metrology. I will discuss how second order Andreev tunneling effects appear in the turnstile measurements and how they are suppressed to enable improvement in accuracy. As a cooler, the bandgap in the superconductor can be used as an energy filter, allowing hot electrons to escape from the normal island and cold electrons to enter the island from the superconductor. This SINIS cooling has potential for replacing other cryogen based refrigeration techniques at low temperatures. One primary aim is to produce a solid-state, cooling platform that cools small devices from 300 to 100 mK.  My most recent research has helped illuminate phonon heating effects that adversely affect the performance of these coolers.