Amperean Pairing Instability in the U(1) Spin Liquid State with Fermi Surface and Application toκ−(BEDT−TTF)2Cu2(CN)3

Recent experiments on the organic compound $\kappa \mathrm{\text{−}}(\mathrm{BEDT}\mathrm{\text{−}}\mathrm{TTF}{)}_2{\mathrm{Cu}}_2(\mathrm{CN}{)}_3$ raise the possibility that the system may be described as a quantum spin liquid. Here we propose a pairing state caused by the “Amperean” attractive interaction between spinons on a Fermi surface mediated by the U(1) gauge field. We show that this state can explain many of the observed low temperature phenomena and discuss testable consequences.