Abstract：We establish a quantum field theory of phase transitions in gapless superconductor CeCoIn$_5$. It is found that uniform Cooper pair gases with pure gradient interactions with negative coefficient can undergo a Bardeen–Cooper–Schrieffer (BCS) condensation below a critical temperature. In the BCS condensation state, bare Cooper pairs with opposite wave vectors are bound into Cooper molecules, and uncoupled bare Cooper pairs are transformed into a new kind of quasiparticle, i.e., the dressed particles. The Cooper molecule system is a condensate or a superfluid, and the dressed particle system is a normal fluid. The critical temperature is derived analytically. The critical temperature of the superconductor CeCoIn$_5$ is obtained to be $T_{\rm c}=2.289$ K, which approaches the experimental data. The transition from the BCS condensation state to the normal state is a first-order phase transition.
. [J]. 中国物理快报, 2019, 36(10): 107401-.
Jiang Hong Man, Ze Cheng. Cooper Molecules: Second Pairing of Cooper Pairs in Gapless Superconductor CeCoIn$_5$. Chin. Phys. Lett., 2019, 36(10): 107401-.
2019, Vol. 36 
