Electronic band structure and momentum dependence of the superconducting gap in (Ca, Na)Fe2As2 from angle-resolved photoemission spectroscopy

TL;DR

This study uses ARPES to explore the electronic structure and superconducting gap in doped CaFe2As2, revealing band-dependent gaps and deviations from expected BCS ratios, which suggest complex pairing mechanisms.

Contribution

It provides detailed ARPES measurements of the band structure and superconducting gaps in (Ca, Na)Fe2As2, highlighting non-trivial relationships between electronic dispersion and superconductivity.

Findings

Band dispersion agrees with theory but shows no Fermi surface nesting.

Superconducting gap is strongly band-dependent below Tc.

BCS ratio at optimal doping is 5.5, lower than related compounds.

Abstract

Electronic structure of newly synthesized single crystals of calcium iron arsenide doped with sodium with Tc ranging from 33 to 14 K has been determined by angle-resolved photoemission spectroscopy (ARPES). The measured band dispersion is in general agreement with theoretical calculations, nonetheless implies absence of Fermi surface nesting at antiferromagnetic vector. A clearly developing below Tc strongly band-dependant superconducting gap has been revealed for samples with various doping levels. BCS ratio for optimal doping, $2\Delta/k_{\rm B}T_{\rm c}=5.5$, is substantially smaller than the numbers reported for related compounds, implying a non-trivial relation between electronic dispersion and superconducting gap in iron arsenides.