Studies on hybrid superconducting junctions
Licentiatavhandling, 2009

In the field of nanoelectronics, one seeks to combine quantum mechanical effects with macroscopic entities such as currents in order to find new ways of storing and manipulating information. One possibility to accomplish this is to use the quantum correlations found in superconductors. Teaming superconductors with normal metals and magnetic systems, one can obtain novel correlation and fluctuation effects. In the first work of this thesis, we examine how charge correlations in a metallic dot are modified due to the presence of a capacitively coupled superconducting island. It is possible to overcome the Coulomb repulsion between electrons in a hybrid double-dot system consisting of a metallic island coupled capacitively to a Cooper-pair box. The superconducting island S acts as a dynamic gate on the metallic island N and in the strong coupling regime the electric charge of the Cooper pairs in S and their fluctuations are able to overscreen the repulsion between electrons in N. This produces an attractive interaction between two additional electrons in the metallic island and results in a non-monotonous charging curve of the metallic island. The second part of the thesis considers how the dynamics of a precessing molecular magnetic moment affects the Josephson current. The precession gives rise to a time-dependent tunnel potential which not only creates different tunneling probabilities for spin-up and spin-down quasiparticles, but also introduces a time-dependent spin-flip term. In particular, we study the effects of the spin-flip term alone on the Josephson current between two spin-singlet superconductors as a function of precession frequency and junction transparency. The system displays a nonequilibrium steady-state solution which depends on the precession frequency of the classical spin.

Critical Current

Single-Electron Box

Attractive Correlations

Josephson Junction

Negative Charging Energy

Quasiclassical Superconductivity

Josephson Current

Fasrummet, MC2
Opponent: Prof. Leonid Gorelik

Författare

Cecilia Holmqvist

Chalmers, Mikroteknologi och nanovetenskap (MC2), Tillämpad kvantfysik

Emergence of a negative charging energy in a metallic dot capacitively coupled to a superconducting island

Physical Review B - Condensed Matter and Materials Physics,; Vol. 77(2008)p. 054517-

Artikel i vetenskaplig tidskrift

Josephson current through a precessing classical spin

Physica B: Condensed Matter,; Vol. 404(2009)p. 527-

Paper i proceeding

Josephson current through a precessing spin

Journal of Physics: Conference Series,; Vol. 150(2009)p. 022027-

Paper i proceeding

Ämneskategorier

Fysik

Den kondenserade materiens fysik

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 149

Fasrummet, MC2

Opponent: Prof. Leonid Gorelik