Regensburg 2019 – scientific programme

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O: Fachverband Oberflächenphysik

O 3: New Methods and Developments I: Scanning Probe Techniques

O 3.8: Talk

Monday, April 1, 2019, 12:15–12:30, H5

Photon-Assisted Tunneling between Superconductors — •Maximilian Uhl, Piotr Kot, Robert Drost, and Christian R. Ast — Max-Planck-Institut für Festkörperforschung, Stuttgart

Microwaves radiated externally into a superconductor tunnel junction of a scanning tunneling microscope influence different kinds of tunneling processes. Here we use a superconducting vanadium tip and sample at a temperature of 300 mK. An external antenna has been designed to produce microwaves in a continuous range from 60 to 90 GHz [2]. It is powered through coaxial cables that are superconducting in the cooled part of the cryostat. The electric field distribution of the antenna radiation depends on the local geometry at the tunnel junction. By emitting and absorbing different numbers of photons, quasiparticles can start tunneling at energies different from the sum of the superconductors’ energy gaps [1, 3]. High resolution measurements of photon-assisted tunneling in dependency of bias voltage, microwave voltage and frequency show that there is a strong transmission of the signal to the antenna. The technique of photon-assisted tunneling measurement is applied to quasiparticle as well as Cooper pair tunneling. Furthermore, it opens up new possibilities for electron spin resonance measurements.

[1] G. Falci, V. Bubanja, G. Schön: Z. Phys. B 85, 451 (1991)

[2] J. Merkt: KIT, Bachelor thesis (2016)

[3] A. Roychowdhury et al.: Phys. Rev. Applied 4, 034011 (2015)