| We have studied NMR of a heavy-fermion superconductor CeCoIn5 which is believed to host a Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state. We direct our attention to newly-discovered SC state of CeCoIn5 in a perpendicular field (H\u2534ab-plane) as well as in a parallel field (H//ab), and present evidences for the FFLO state in both cases as well. NMR spectra at the Co, In(1), and In(2) sites have been measured in a wide frequency range for H\u2534ab. Upon entering the new SC state at high field and low temperature region, NMR spectra change dramatically below T(Hc) in the case of H\u2534ab as well as H//ab. NMR spectra at two separated- positions persist down to the lowest temperature (~100mK), which indicates the appearance of a nordal plane structure of superconducting gap. We find the critical field HFFLO separating the FFLO and the BCS state lies in a very narrow range between 4.65 T and 4.70 T below Tc(H). We will discuss also strong Pauli paramagnetic effects on the temperature and field dependences of the Knight shift in the vicinity of the first order transition at HC2. |
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