A new field combining spintronics and molecular electronics, molecular spintronics, is emerging due the development of the production of molecular magnetic materials. Even single-molecule magnets (SMM), which can be integrated into nanoscale electronic devices, have been produced. SMMs open up the prospect of storing information on a molecular level as well as utilizing quantum properties of matter to manipulate this information. One possibility is to use the quantum correlations found in superconducting devices. Investigating superconducting nanoscale systems combining quantum transport and spin interactions will become increasingly important as experimental research progresses.
In this project we study how the dynamics of a precessing molecular magnetic moment affects the Josephson current. The system can be realized e.g. by contacting a carbon nanotube to superconducting leads and placing a SMM on top of the nanotube. Application of a magnetic field causes the magnetic moment to perform Larmor precession, which 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. If the precession is confined to the xy plane, the spin-flip tunneling causes a π-shift in the current-phase relation of the Josephson current, as well as a non-equilibrium distribution of the Andreev scattering states leading to the abrupt steps in the current.
Reference: C. Holmqvist, S. Teber, M. Houzet, D. Feinberg, M. Fogelström, Journal of Physics: Conf. Ser. 150 022027 (2009) S. Teber, C. Holmqvist, M. Houzet, D. Feinberg, M. Fogelström, Physica B: Condensed Matter, 404 pp. 527 (2009) C. Holmqvist, Licentiate thesis (2009)