Non-Fermi-Liquid Behavior in CeCoIn₅ Near the Superconducting Critical Field

We measured specific heat and resistivity of heavy fermion CeCoIn5 at and above the superconducting critical field with field in [001] (Hc2 = 5 T) and [100] directions (Hc2 = 12 T), and at temperatures down to 50 mK. At the critical fields the data show Non Fermi Liquid (NFL) behavior down to the lowest temperatures. With increasing field the data exhibit crossover from NFL to Fermi liquid behavior at the lowest temperatures. Analysis of the scaling properties of the specific heat, and comparison of both resistivity and the specific heat with the predictions of a spinfluctuation theory suggest that the NFL behavior is due to incipient antiferromagnetism (AF) in CeCoIn5, with the quantum critical point in the vicinity of Hc2. Below Hc2 the AF phase which competes with the paramagnetic ground state is superseded by the superconducting transition. To separate the quantum critical point HQCP from the superconducting critical field Hc2 we performed a series of Sn-doping and hydrostatic pressure studies. Sn-doping appears not to be able to separate HQCP and Hc2. Preliminary resistivity in magnetic field measurements under hydrostatic pressure indicate that the QCP point moves inside the superconducting phase in the H-P plane with increasing field.