Field-Induced Quantum Critical Point in CeCoIn₅

The resistivity of the heavy-fermion superconductor CeCoIn₅ was measured as a function of temperature, down to 25 mK and in magnetic fields of up to 16 T applied perpendicular to the basal plane. With increasing field, we observe a suppression of the non-Fermi liquid behavior, ρ∼T, and the development of a Fermi liquid state, with its characteristic ρ=ρ₀+AT² dependence. The field dependence of the T² coefficient shows critical behavior with an exponent of 1.37. This is evidence for a field-induced quantum critical point (QCP), occurring at a critical field which coincides, within experimental accuracy, with the superconducting critical field H_c2. We discuss the relation of this field-tuned QCP to a change in the magnetic state, seen as a change in magnetoresistance from positive to negative, at a crossover line that has a common border with the superconducting region below ∼1  K.