Nodelessd-wave superconductivity in a quasi-one-dimensional organic superconductor under anion order

Abstract

We propose a mechanism of nodeless d-wave superconductivity in a quasi-one-dimensional organic superconductor under anion order. It is shown that a split of the Fermi surfaces due to the anion order eliminates the line nodes of a d-wave gap function on the Fermi surfaces, and a small finite energy gap appears in the quasiparticle excitations of superconductivity. We discuss that temperature dependences of thermal conductivity and the NMR relaxation rate observed in a quasi-one-dimensional organic superconductor $(\mathrm{TMTSF}{)}_{2}{\mathrm{ClO}}_{4}$ can be explained consistently by the small energy gap.