Anomalous thermopower and Nernst effect in CeColn₅: Loss of entropy current in precursor state

The heavy-electron superconductor CeCoIn₅ exhibits a puzzling precursor state above its superconducting critical temperature at T _c≤2.3 K. The thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of the electrons undergoes a steep decrease reaching ∼0 at T_c. Concurrently, the off-diagonal thermoelectric current α_xy is enhanced. The delicate sensitivity of the zero-entropy state to field implies phase coherence over large distances. The prominent anomalies in the thermoelectric current contrast with the relatively weak effects in the resistivity and magnetization.