Phenomenological theory of the s-wave state in superconductors without an inversion center

In materials without an inversion center of symmetry the spin degeneracy of the conducting band is lifted by an antisymmetric spin orbit coupling (ASOC). Under such circumstances, spin and parity cannot be separately used to classify the Cooper pairing states. Consequently, the superconducting order parameter is generally a mixture of spin singlet and triplet pairing states. In this paper we investigate the structure of the order parameter and its response to disorder for the most symmetric pairing state (A<Subscript>1</Subscript>). Using the example of the heavy Fermion superconductor CePt<Subscript>3</Subscript>Si, we determine characteristic properties of the superconducting instability. Depending on the type of the pairing interaction, the gap function is characterized by the presence of line nodes. We show that this line nodes move in general upon temperature. Such nodes would be essential to explain recent low-temperature data of thermodynamic quantities such as the NMR-T<Subscript>1</Subscript> <Superscript>-1</Superscript>, London penetration depth, and heat conductance. Moreover, we study the effect of (non-magnetic) impurity on the superconducting state. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006