On the superconducting state of the organic conductor $(TMTSF{)}_{2}Cl{O}_4$

Abstract

$(TMTSF{)}_{2}Cl{O}_4$ is a quasi-one dimensional organic conductor and superconductor with $T_c=1.4$K, and one of at least two Bechgaard salts observed to have upper critical fields far exceeding the paramagnetic limit. Nevertheless, the ${}^{77}$Se NMR Knight shift at low fields reveals a decrease in spin susceptibility $\ddot{I}{‡}_s$ consistent with singlet spin pairing. The field dependence of the spin-lattice relaxation rate at 100mK exhibits a sharp crossover (or phase transition) at a field $H_s\sim 15$kOe, to a regime where $\ddot{I}{‡}_s$ is close to the normal state value, even though \hc2 $\gg H_s$.

4 pages, 4 figures, Version 2: 2 sentence ammendaments on the last page, changes in references, corrected untits in Fig. 3.