Condensed-Matter Physics & Materials Science Seminar

We discuss the Feshbach shape resonance in the exchange-like interband pairing term as the possible mechanism for high Tc. It occurs in multiband superconductivity as a resonance in the configuration interaction between different pairing channels in different subbands. ARPES of curpates show the coexistence of two different subbands at the Fermi level due to nanoscale phase separation forming a superlattice of quantum stripes. In the superlattices the different spatial location and disparity of the wavefunction symmetry of the two components make possible the interband exchange pairing. The shape resonance occurs at dimensional electronic topological transitions. The high Tc maximum is reached at the Feshbach shape resonance for the 1D to 2D electronic topological transition (1D/2D ETT) in the electronic spectrum in the superlattice of quantum stripes. A BCS to BOSE-like transition occurs going from 2D to 1D side of the ETT. We report the evidence for Feshbach shape resonance in electron doped MgB{2}, a multiband superconductor in the clean limit that provides the simplest high Tc (40K) superconducting system (HTcS) playing the role of atomic hydrogen for HTcS. The exchange pairing at the 2D to 3D Lifshitz electronic topological transistion (2D/3D ETT) is shown to be the key term controlling the increase of the critical temperature from 0.3K to 40K as confirmed by recent Raman data.