title: Field dependence of the ground state in the exotic superconductor CeCoIn5: a nuclear magnetic resonance investigation.
abstract: We report 115In nuclear magnetic resonance (NMR) measurements in CeCoIn5 at low temperature (T approximately 70 mK) as a function of the magnetic field (H0) from 2 to 13.5 T applied perpendicular to the c axis. A NMR line shift reveals that below 10 T the spin susceptibility increases as sqrt[H0]. We associate this with an increase of the density of states due to the Zeeman and Doppler-shifted quasiparticles extended outside the vortex cores in a d-wave superconductor. Above 10 T a new superconducting state is stabilized, possibly the modulated phase predicted by Fulde, Ferrell, Larkin, and Ovchinnikov. This phase is clearly identified by a strong and linear increase of the NMR shift with the field, before a jump at the first order transition to the normal state.
authors.affiliation: Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: G
authors.initials: G
authors.lastname: Koutroulakis
authors.forename: V F
authors.initials: VF
authors.lastname: Mitrović
authors.forename: M
authors.initials: M
authors.lastname: Horvatić
authors.forename: C
authors.initials: C
authors.lastname: Berthier
authors.forename: G
authors.initials: G
authors.lastname: Lapertot
authors.forename: J
authors.initials: J
authors.lastname: Flouquet