Quasiparticle Entropy in the High-Field Superconducting Phase ofCeCoIn5

Y. Tokiwa, E. D. Bauer, P. Gegenwart
2012 Physical Review Letters  
The heavy-fermion superconductor CeCoIn$_5$ displays an additional transition within its superconducting (SC) state, whose nature is characterized by high-precision studies of the isothermal field dependence of the entropy, derived from combined specific heat and magnetocaloric effect measurements at temperatures $T\geq 100$ mK and fields $H\leq 12$ T aligned parallel, perpendicular and $18^\circ$ off the tetragonal [100] direction. For any of these conditions, we do not observe an additional
more » ... rve an additional entropy contribution upon tuning at constant temperature by magnetic field from the homogeneous SC into the presumed Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) SC state. By contrast, for $H\parallel [100]$ a negative isothermal entropy contribution, compatible with spin-density-wave (SDW) ordering, is found. Our data exclude the formation of a FFLO state in CeCoIn$_5$ for out-of-plane field directions, where no SDW order exists.
doi:10.1103/physrevlett.109.116402 pmid:23005654 fatcat:fqj25fz2jrdbxfvcjhkcbj332u