Small gap or Nodal gap in Iron-based superconductors ?

Yunkyu Bang

In this talk, I will review the current experiments of the Fe-based superconductors and their compatibility with the +/-s-wave gap with small gap and nodal gap. First, I will discuss the field dependence of the thermal conductivity \kappa(T ,H)/T and specific heat coefficient \gamma(H) = C(T,H)/T data of Ba(Fe1-xCox)2As2 and their explanation by the +/-s-wave state. Then I will critically examine the experiments of LaFePO, BaFe2(AsP)2, and KFe2As2 for their compatibility with a nodal gap which is mostly claimed.