c-axis magnetotransport in CeCoIn5 -: art. no. 184506

We present the results of out-of-plane electrical transport measurements on the heavy fermion superconductor CeCoIn5 at temperatures from 40 mK to 400 K and in magnetic field up to 9 T. For T < 10 K transport measurements show that the zero-field resistivity rho(c) changes linearly with temperature and extrapolates nearly to zero at 0 K, indicative of non-Fermi-liquid (NFL) behavior associated with a quantum critical point (QCP). The longitudinal magnetoresistance (LMR) of CeCoIn5 for fields applied parallel to the c axis is negative and scales as B/(T+T-*) between 50 and 100 K, revealing the presence of a single-impurity Kondo energy scale T-*similar to 2 K. Beginning at 16 K a small positive LMR feature is evident for fields less than 3 T that grows in magnitude with decreasing temperature. For higher fields the LMR is negative and increases in magnitude with decreasing temperature. This sizable negative magnetoresistance scales as B-2/T from 2.6 K to roughly 8 K, and it arises from an extrapolated residual resistivity that becomes negative and grows quadratically with field in the NFL temperature regime. Applying a magnetic field along the c axis with B > B-c2 restores Fermi-liquid behavior in rho(c)(T) at T less than 130 mK. Analysis of the T-2 resistivity coefficient's field dependence suggests that the QCP in CeCoIn5 is located below the upper critical field, inside the superconducting phase. These data indicate that while high-T c-axis transport of CeCoIn5 exhibits features typical for a heavy-fermion system, low-T transport is governed both by spin fluctuations associated with the QCP and Kondo interactions that are influenced by the underlying complex electronic structure intrinsic to the anisotropic CeCoIn5 crystal structure.