Dresden 2014 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 73: Scanning Probe Methods II
O 73.4: Vortrag
Donnerstag, 3. April 2014, 11:15–11:30, WIL A317
The STM as Microwave resonator: Josephson currents interacting with the environment — •Berthold Jäck1, Matthias Eltschka1, Maximilian Assig1, Markus Etzkorn1, Christian R. Ast1, and Klaus Kern1,2 — 1Max-Planck-Institute for Solid State Research, D-70569 Stuttgart — 2École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne
We investigated the Josephson Effect in Vanadium tunnel junctions by using an STM operating at a temperature of 15 mK [1]. As the STM junction geometry is of very small capacitance our measured current-voltage characteristics exhibit clear indications for Coulomb blockade dominated tunneling in the overdamped regime. Next to the supercurrent we observe harmonic sub-gap features at energies of about 100 *eV. By varying the STM tip length and the tip-sample geometry we are able to tune both resonance energy as well as its intensity. We explain these findings with photon-assisted tunneling of Cooper pairs driven by an electro-magnetic mode localized on the STM tip. The mode is excited by GHz radiation which is emitted from the Josephson junction driven in the AC regime. Our physical picture is substantiated with finite-element-method simulations on the electro-dynamic properties of our 3D tip-sample geometry. We will discuss these findings in the framework of Josephson junctions coupled to an electro-magnetic environment [2] and also give an outlook in view of possible applications as GHz-source on the atomic scale.
[1] M. Assig et al., Rev. Sci. Instrum. 84, 033903 (2013)
[2] G.-L. Ingold et al., Phys. Rev. B 50, 1 (1994)