Conductance spectroscopy of a correlated superconductor in a magnetic field in the Pauli limit: Evidence for strong correlations

Abstract

We study conductance spectroscopy of a two-dimensional junction between a normal metal and a strongly correlated superconductor (SC) in an applied magnetic field in the Pauli limit. Depending on the field strength, the SC is either in the Bardeen-Cooper-Schrieffer (BCS) or in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state of the Fulde-Ferrell type. The strong correlations are accounted for by means of the Gutzwiller method, which naturally leads to the emergence of the spin-dependent masses of quasiparticles when the system is spin polarized. The case without strong correlations (with the spin-independent masses) is analyzed for comparison. We consider both the s-wave and the d-wave symmetries of the SC gap and concentrate on the parallel orientation of the Cooper-pair momentum Q with respect to the junction interface. The junction conductance is presented for selected barrier strengths (i.e., in the contact, the intermediate, and the tunneling limits). The conductance spectra in the cases with and without strong correlations differ essentially. Thus, our analysis provides an experimentally accessible test for the presence of strong correlations in the SC state. Namely, correlations alter the distance between the conductance peaks (or related conductance features) for carriers with spin up and spin down. In the uncorrelated case, this distance is twice the Zeeman energy. In the correlated case, the corresponding distance is about 30%–50% smaller, but other models may provide even stronger differences, depending on the details of the system’s electronic structure. It turns out that the strong correlations manifest themselves most clearly in the case of the junction with the BCS, rather than the FFLO SC, what should make the experimental verification of the present results simpler.

Source-reported materials — not catalogue approval

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