Field Dependence of the Ground State in the Exotic Superconductor CeCoIn${}_5$: a Nuclear Magnetic Resonance Investigation

Abstract

We report ${}^{115}$In nuclear magnetic resonance (NMR) measurements in CeCoIn${}_5$ at low temperature ($T\approx 70$ mK) as a function of magnetic field ($H_0$) from 2 T to 13.5 T applied perpendicular to the $\hat{c}$-axis. NMR line shift reveals that below 10 T the spin susceptibility increases as $\sqrt{H_0}$. 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 (FFLO). 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.

4 pages, to appear in Phys. Rev. Lett

References in corpus (6)

• Calorimetric Evidence for a Fulde-Ferrell-Larkin-Ovchinnikov Superconducting State in the Layered Organic Superconductor κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$
• Unpaired Electrons in the Heavy-Fermion Superconductor CeCoIn_{5}
• Interacting Antiferromagnetic Droplets in Quantum Critical CeCoIn_5
• Observation of Spin Susceptibility Enhancement in the Possible FFLO State in CeCoIn${}_5$
• Vortex state in a Fulde-Ferrell-Larkin-Ovchinnikov superconductor based on the quasiclassical theory
• Phase Diagram of CeCoIn_5 in the Vicinity of H_{c2} as Determined by NMR

Cited by in corpus (2)

• Nuclear magnetic resonance in the heavy fermion superconductors
• Evolution of the spin resonance in CeCoIn${}_5$ under magnetic field