Optical sum rule in multiband superconductors

Particular type of a gap in the spectrum of multiband superconductors

“…general mechanism of the composite gap opening, that qualitatively explains our previous results for slow increase of the conductivity spectral weight with frequency cutoff growing in the two-band model [23].…”

“…Since it is assumed that these bands are formed by the atomic orbitals of different types of symmetry, the matrix element of hybridization between them is a strongly anisotropic function of quasimomentum t ac (k) = t 0 ac (cos k x − cos k y ) [22]. (It is not crucial for the discussed effect but it is closely related to our previous results [23]). The calculations were performed with the following values of the parameters of the two-band model: t a = 30, t c = −1, t 0 ac = 5, ∆ a = −0.18, ∆ c = 0.81 (in units of |t c |).…”