J. Phys. IV France
Volume 131, December 2005
Page(s) 49 - 54
Published online 18 January 2006
International Workshop on Electronic Crystals
S. Brazovskii, P. Monceau and N. Kirova
J. Phys. IV France 131 (2005) 49-54

DOI: 10.1051/jp4:2005131010

Feshbach shape resonances in nanoscale multiband systems for high Tc superconductivity

M. Filippi1, A. Bianconi1 and A. Bussmann-Holder2

1  Department of Physics, University of Rome La Sapienza, Ple. A. Moro 2, 00185 Roma, Italy
2  Max-Planck-Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany

We show that electron doped MgB2, made of a superlattice of boron honeycomb layers, is a multiband superconductor in the clean limit that provides the simplest high T$_{\rm
c}$ superconducting system (HTcS) called also the atomic hydrogen for HTcS. The chemical potential has been tuned by atomic substitution keeping the superconductivity in the clean limit. This is a two component electronic system made of a first Fermi gas in the $\pi $ subband that coexists with a second low density electron fluid in the $\sigma
$ subband close the localization limit $5<{\rm r}_{\rm s}<30$. The Feshbach shape resonance of the interband exchange-like pairing term centered at the 2D to 3D Lifshitz electronic topological transition ($\rm 2D/3D$ ETT) is shown to be the key term controlling the critical temperature in the range from 0.3 K to 40 K.

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