Observation of Spatially Modulate Superconductivity

CeCoIn5 is a well-known d-wave superconductor heavy fermion presenting a unique phase diagram. For a certain orientation of the magnetic field, a second superconducting phase, called Q phase, appears only below 300 mK and for fields close to the upper critical field. This phase sees a coexistence of superconductivity and magnetic order. The nature of the superconductivity remains uncertain, and different theories have been proposed from FFLO to the influence of the nearby magnetic quantum critical point.

 

We present NMR measurements done on In sites at high field in the Q phase.  These measurements provide clear evidence of the coexistence of an exotic superconducting state and the incommensurate long-range magnetic order. We infer that this exotic superconducting phase that coexists with magnetic order is characterized by the Andreev bound states formed by spin-polarized quasiparticles spatially localized in the nodes of the order parameter.