Prof. Thierry Martin (CPT and Universite de la Mediterranee)
"Superconducting transport through a vibrating molecule"
I will discuss two topics associated with Cooper pair transport through a
molecular quantum dot with vibrational degrees of freedom. First, I will
study the subgap transport in the presence of a finite bias, in the
multiuple Andreev reflection (MAR) regime. Nonequilibrium Green functions
are used to compute the current in the weak coupling regime with phonons. In
the subgap regime, MAR processes are accompanied by phonon emission, and
thus give rise to an even-odd parity effect that can be interpreted in terms
of an inelastic MAR ladder picture. Second, I will show that at zero bias,
in the presence of strong phonon coupling, the Josephson current can operate
as a mechanism to compress the vibrational state of the molecule. The
ground-state solution is obtained "exactly" in the limit of a large
superconducting gap. Coherent charge fluctuations are entangled with
non-classical phonon states. The Josephson current thus induces squeezing of
the phonon mode, which is controlled by the superconducting phase difference
and by the junction asymmetry.
[1] Phonon Squeezing in a Superconducting Molecular Transistor, A. Zazunov,
D. Feinberg, and T. Martin, Phys. Rev. Lett. 97, 196801 (2006).
[2] Superconducting transport through a vibrating molecule, A. Zazunov, R.
Egger, C. Mora, and T. Martin, Phys. Rev. B 73, 214501 (2006).