Temperature dependence of the superfluid density as a probe for multiple gaps inBa(Fe0.9Co0.1)2As2: Manifestation of three weakly interacting condensates

Abstract

The knowledge about the gap size and structure is of utmost importance for a theory of the superconducting pairing mechanism. The number of superconducting gaps is an important part of the description and modeling of multiband systems such as the iron-based superconductors. Here, we present a study on the temperature dependence of the superfluid density, ${\ensuremath{\rho}}_{\mathrm{s}}(T)$, in ${\mathrm{Ba}(\mathrm{Fe}}_{0.9}{\mathrm{Co}}_{0.1}){}_{2}{\mathrm{As}}_{2}$ obtained from terahertz spectra of conductivity and dielectric permittivity of thin film samples with critical temperatures ${T}_{\mathrm{c}}\ensuremath{\approx}20--22$ K. We demonstrate that the temperature dependence of the superfluid density, ${\ensuremath{\rho}}_{\mathrm{s}}(T)$, can be explained best by a model of three interacting superconducting condensates. Our results refine the standard two-band approach for Co-doped ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$.