Microscopic evidence of the FFLO state in CeCoIn₅ probed by NMR

We found an anomalous temperature dependence of ¹¹⁵In-NMR spectrum in the newly discovered high field and low-temperature superconducting phase of CeCoIn₅. The anomalies near the upper limit of H_{c 2} are attributed to spatially distributed local density of states of quasiparticles. From a simulation model with sinusoidally modulated superconducting order parameter, the present NMR study at a microscopic point of view provides a direct evidence that the Fulde-Ferrell-Larkin-Ovchinikov (FFLO) state is realized at the high-field phase in CeCoIn₅.