Field-tuned quantum critical point in CeCoIn5 near the superconducting upper critical field

We report a systematic study of high-magnetic-field specific heat and resistivity in single crystals of CeCoIn5 for the field oriented in the basal plane (H parallel to ab)of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T-2 law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H parallel to c), the emergent picture is that of a magnetic-field-tuned quantum critical point which exists in the vicinity of the superconducting H-c2(0) despite a variation of a factor of 2.4 in H-c2(0) for different field orientations. This suggests that an underlying physical reason exists for the superconducting H-c2(0) to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi-liquid ground state with increasing magnetic field is more!
gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in plane. Together with the close proximity of the quantum critical point and H-c2(0) in CeCoIn5 for both field orientations, the anisotropy in the recovery of the Fermi-liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical.