Momentum-resolved superconducting gap in the bulk of Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ from combined ARPES and $\mu$SR measurements

TL;DR

This study combines ARPES and $$SR measurements to accurately model the superconducting gap and penetration depth in Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$, confirming ARPES as a bulk-sensitive technique and revealing two nearly isotropic gaps in hole-doped iron superconductors.

Contribution

It provides a parameter-free calculation of the temperature-dependent London penetration depth using ARPES data and validates ARPES as representative of bulk properties in BKFA.

Findings

Calculated $$L(T)$$) matches experimental data.

Identified two nearly isotropic superconducting gaps in hole-doped iron superconductors.

Established ARPES as a bulk-representative measurement technique.

Abstract

Here we present a calculation of the temperature-dependent London penetration depth, $\lambda(T)$, in Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ (BKFA) on the basis of the electronic band structure [1,2] and momentum-dependent superconducting gap [3] extracted from angle-resolved photoemission spectroscopy (ARPES) data. The results are compared to the direct measurements of $\lambda(T)$ by muon spin rotation ($\mu$SR) [4]. The value of $\lambda(T=0)$, calculated with \emph{no} adjustable parameters, equals 270 nm, while the directly measured one is 320 nm; the temperature dependence $\lambda(T)$ is also easily reproduced. Such agreement between the two completely different approaches allows us to conclude that ARPES studies of BKFA are bulk-representative. Our review of the available experimental studies of the superconducting gap in the new iron-based superconductors in general allows us to state that all hole-doped of them bear two nearly isotropic gaps with coupling constants $2\Delta/k_{\rm B}T_{\rm c}=2.5\pm1.5$ and $7\pm2$.