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Séminaire MCBT

Mardi 4 juin à 11h00,
Salle Nevill Mott, D420.

Orateur : Julius Ranninger (Institut NEEL)
"The mechanism/material independent criteria that differentiate the cuprate from the BCS superconductors"

This is the first of a series of lectures I was asked to deliver. I will start by recalling how the electromagnetic gauge symmetry breaking - i.e. the ultimate cause for achieving superconductivity - manifests itself in the magnetic-field expulsion (Meissner-Ochsenfeld effect). The conjectured London equations explain this experimental finding by accounting for (i) the initially massless electromagnetic field being rendered massive by the flow of super-currents and (ii) the generation of a longitudinal massive helicity-0 component of the field, that assures the persistence of the super-current flow. Electromagnetic gauge symmetry breaking arises from the infinite polarizability of the normal state in both BCS and cuprate superconductors. It results in an interplay between fluctuations of the charge current and the accompanying electromagnetic field excitations - being monitored by generalized gauge transformations only ! Then I will show that the equations controlling this interplay are identical to the London equations, as illustrated by Ranninger and Thirring in 1963. On such a basis, Weinberg in 1986 illustrated how the robust macroscopic material/mechanism independent features of superconductors can be encoded in a simple generic Lagrangian that depends on the fundamental physical constants of nature only (e, \hbar, c).

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