Field dependence of the ground state in the exotic superconductor CeCoIn5: a nuclear magnetic resonance investigation.
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.
Koutroulakis
G
G
Department of Physics, Brown University, Providence, Rhode Island 02912, USA.
Mitrović
V F
VF
Horvatić
M
M
Berthier
C
C
Lapertot
G
G
Flouquet
J
J