Isotropic multi-gap superconductivity in BaFe1.9Pt0.1As2 from thermal transport and spectroscopic measurements

TL;DR

This study combines thermal transport, spectroscopic, and photoemission measurements to demonstrate isotropic multi-gap superconductivity in BaFe1.9Pt0.1As2, revealing a consistent 3 meV gap and a larger secondary gap, with no nodes or minima.

Contribution

The paper provides comprehensive multi-technique evidence for isotropic multi-gap superconductivity in BaFe1.9Pt0.1As2, highlighting the gap structure and its implications for the superconducting order parameter.

Findings

Absence of quasiparticle excitations at T=0 up to 15 T

Identification of a 3 meV isotropic gap on electron and hole pockets

Evidence for a second, larger superconducting gap

Abstract

Thermal conductivity, point contact spectroscopy, angle-resolved photoemission and Raman spectroscopy measurements were performed on BaFe1.9Pt0.1As2 single crystals obtained from the same synthesis batch in order to investigate the superconducting energy gap structure using multiple techniques. Low temperature thermal conductivity was measured in the superconducting state as a function of temperature and magnetic field, revealing an absence of quasiparticle excitations in the T=0 limit up to 15 T applied magnetic fields. Point-contact Andreev reflection spectroscopy measurements were performed as a function of temperature using the needle-anvil technique, yielding features in the conductance spectra at both 2.5 meV and 7.0 meV scales consistent with a multi-gap scenario. Angle-resolved photoemission spectroscopy probed the electronic band structure above and below the superconducting transition temperature of T_c=23 K, revealing an isotropic gap of magnitude ~3 meV on both electron and hole pockets. Finally, Raman spectroscopy was used to probe quasiparticle excitations in multiple channels, showing a threshold energy scale of 3 meV below T_c. Overall, we find strong evidence for an isotropic gap structure with no nodes or deep minima in this system, with a 3 meV magnitude gap consistently observed and a second, larger gap suggested by point contact spectroscopy measurements. We discuss the implications that the combination of these results reveal about the superconducting order parameter in the BaFe1-xPtxAs2 system and how this relates to similar substituted iron pnictides.