## Two-band parallel conductivity at terahertz frequencies in the superconducting state of MgB$_2$.

Ortolani, M.
Dore, P.
Di Castro, D.
Perucchi, A.
Lupi, S.
Ferrando, V.
Putti, M.
Pallecchi, I.
Ferdeghini, C.
Xi, X. X.
##### Description
The optical response of the two-band superconductor MgB$_2$ has been studied in the 0.7-4 THz range on films with very low impurity level. The effect of the high-energy $\sigma$-gap is observed in the ratio $R_S/R_N$ between the normal and superconducting state reflectance, while in a neutron irradiated film with a slightly higher impurity level mainly the effect of the $\pi$-gap is evident as reported in previous experiments. At terahertz frequencies, the electrodynamic of MgB$_2$ can be well described by the two-band parallel conductivity model and is dominated by the $\pi$-bands when the impurity level is only slightly higher than that of an ultra-clean sample.
Comment: 4 pages, 3 figures
##### Keywords
Condensed Matter - Superconductivity