Local characterization of a heavy-fermion superconductor via sub-Kelvin magnetic force microscopy

Abstract

Using magnetic force microscopy operating at sub-Kelvin temperatures, we characterize the heavy fermion superconductor CeCoIn5. We pinpoint the absolute London penetration depth of lambda ( 0 ) = 435 +/- 20 nm and report its temperature dependence, which is closely linked to the symmetry of the superconducting gap. In addition, we directly measure the pinning force of individual Abrikosov vortices and estimate the critical current density of j c = 9 x 10 4A/cm(2). In contrast to the related, well-established tunnel diode oscillator technique, our method is capable of resolving inhomogeneities locally on the micrometer scale at ultra-low temperature.