Superconducting Nanocircuits | Quantum Dissipative Systems | Quantum communication | Coherent control of quasiparticles in graphene | Further research lines |
Hybrid Nanosystems
A fascinating aspect
of mesoscopics is the possibility of fabricating hybrid
nanostructures formed from combinations of
normal-metals,
superconductors and ferromagnets.
This allows one to explore a rich variety of quantum
phenomena.
For example, normal-metal/ferromagnet interfaces
bring novel physics associated with the introduction of spin-dependent
transport, resulting in the
striking phenomenon of Giant
Magnetoresistance in magnetic multilayers and spin-valves.
As a result, a new field of research has opened, referred to as spintronics,
where the spin of electrons is exploited together with
their charge.
The potential application of spintronics is very broad, going from
magnetic
recording and position sensor technology, to the physical
implementation of quantum computation, which would exploit the
extremely long
spin coherence length.
As a second example,
the extra physics introduced by the presence of superconducting metals
has
driven a resurgence of interest in
Andreev scattering, an additional process consisting
of the coherent evolution of a particle-like excitation into a
hole-like
excitation and vice versa.
During the last few years the interplay between these two different
mechanisms
has been observed in
numerous experimental studies of electronic transport
properties in nanostructures containing both ferromagnets and
superconductors.
We have investigated the following topics:
- Spin filtering in ferromagnet/superconductor ballistic nanojunctions
- Correlations in multiterminal hybrid systems
Josephson Junction Arrays
Nano-scale superconducting networks and low-capacitance Josephson junction arrays display a wealth of novel physics, in particular in their dynamic behavior, the properties of their collective excitations, and their unusual classical or quantum phase transitions. Low-temperature and advanced measuring techniques allow the resolution of spatial structures and the study of the system dynamics. Recently quantum-mechanical properties of the collective excitations in arrays, namely charges and vortices, have been demonstrated. Josephson Junction arrays and networks are interesting as physical realizations with controllable parameters of statistical mechanics systems such as the XY and Bose-Hubbard models. Very general and universal concepts can be studied. A few of these phenomena are: vortex melting, Kosterlitz-Thouless(KT) and metal-insulator transitions, frustration, commensurability, etc. Apart from their importance for physics, superconducting circuits are interesting from a technological point of view. The fabrication of large arrays of mesoscopic units requires simultaneous control of processes on small and large scales.
Small Grains
Thermodynamic and
transport properties of small metallic systems depend
on the parity of the electron number. In normal
metal grains, these even-odd effects are observed when the temperature
is lowered below the average level spacing, which is inversely
proportional to the volume of the grain.
The possibility of experimental investigations of nanometre grains
has stimulated a lot of attention in understanding how collective
effects (superconductivity for instance) are modified by reducing the
system size. Properties of interacting systems in the canonical
ensemble
can differ substantially from bulk behaviour. Intensively investigated
systems are superconducting and ferromagnetic grains.
Research activities focussed on:
- Thermodynamic properties of superconducting grains
- Interplay between superconductivity and ferromagnetism in nanometer size grains