Laboratory of Theoretical and Experimental Superconductive Tunnelling

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Fundamental study of unconventional superconductors
	Calculations within the Eliashberg theory The BCS theory describes well conventional superconductors in which the pairing is mediated by phonons and the electron-phonon coupling is rather weak. In most unconventional superconductors, the electron-boson coupling is strong and this has a series of consequences that cannot be explained within the BCS theory. The Eliashberg theory is more general than BCS and allows describing both weak-coupling and strong-coupling superconductors.  Moreover, it can be adapted to describe (at least in a semi-phenomenological way) systems in which the coupling is mediated by any kind of bosonic excitations. We use the Eliashberg theory to: test the consistency of the experimentally-determined critical temperature and gap amplitudes within a given microscopic model for the superconducting pairing determine the coupling strength and the dominant coupling channels (in multiband superconductors) calculate the density of states as a function of the electron-boson spectral function and of the symmetry of the order parameter analyze the strong electron-boson interaction (EBI) features in the point-contact spectra (from tunnelling to Andreev regime) calculate the energy-dependent complex gaps that can be inserted into the BTK model to fit the EBI in experimental point-contact spectra predict the effect of charge doping or chamical doping on the superconducting properties (critical temperature, gaps, critical field, etc) predict or analyze the effect of disorder or impurities (either magnetic or non-magnetic) on various superconducting properties (Tc, gap, critical fields, etc) calculate several quantities of experimental interest to be compared with results in literature. In particular, three- or four-band effective models, with dominant repulsive interband coupling, have been developed to describe iron-based compounds of the 1111, 122, 111 families. <back	Experimental (symbol) and theoretical (lines) behaviour of the gaps of Mn-doped MgB2 as a function of the critical temperature
		Effect of disorder induced by self-irradiation: Critical temperature as a function of the residual resisitivity in PuCoGa5 (symbols) compared to the predictions of Eliashberg theory for s-wave and d-wave order parameter.
		Gaps and critical temperature in Ba(Fe,Co)2As2, as a function of the Co content. Comparison of experimental values and predictions of the three-band Eliashberg model.

LaTEST - Department of Applied Science and Technology, Politecnico di Torino
corso Duca degli Abruzzi 24, 10129 Torino (TO) - Italy