Anomalous superconductivity and field-induced magnetism in CeCoIn 5

In the heavy fermion superconductor ${\mathrm{CeCoIn}}_{5}$ ${(T}_{c}=2.3 \mathrm{K})$ the critical field is large, anisotropic, and displays hysteresis. The magnitude of the critical-field anisotropy in the $a\ensuremath{-}c$ plane can be as large as 7 T and depends on orientation. Critical-field measurements in the (110) plane suggest two-dimensional superconductivity, whereas conventional effective-mass anisotropy is observed in the (100) plane. Two distinct field-induced magnetic phases are observed: ${H}_{a}$ appears deep in the superconducting phase, while ${H}_{b}$ intersects ${\mathrm{Hc}}_{2}$ at $T=1.4 \mathrm{K}$ and extends well above ${T}_{c}.$ These observations suggest the possible realization of a direct transition from ferromagnetism to Fulde-Ferrel-Larkin-Ovchinnikov superconductivity in ${\mathrm{CeCoIn}}_{5}.$