Investigation of Iron-Based and Topological Superconductors via Point-Contact Spectroscopy

Abstract

I report results of point-contact spectroscopy (PCS) measurements preformed on a variety of superconductors which are predicted to exhibit unconventional Cooper pairing mechanisms. Point-contact spectra of the iron pnictide BaFe_{1-x}$Pt$_x$As$_2$ are consistent with a two-gap isotropic s-wave model. This conclusion is supported by previously published results from thermal conductivity, angle-resolved photoemission spectroscopy (ARPES), and Raman spectroscopy, which confirm a lack of nodes in the order parameter and the presence of a gap of magnitude 3 meV. Conductivity spectra were also measured for the half-Heusler materials YPtBi and LuPdBi using the soft point contact method. I argue that the repeated observation of a single peak in $dI/dV$ at zero bias is not consistent with a conventional $s$-wave model. Based on attempts to fit my data to the Blonder-Tinkham-Klapwijk theory and comparison to previous experimental and theoretical work, I conclude that my results are most consistent with a model of triplet Cooper pairs and an order parameter with an odd-parity component.