# Two-Gap Superconductivity in CaFe_{0.88}Co_{0.12}AsF Revealed by Temperature Dependence of the Lower Critical Field H_{c1}^c(T)

## TL;DR

This study uncovers two-gap superconductivity in CaFe_{0.88}Co_{0.12}AsF through temperature-dependent measurements of the lower critical field, revealing key gap magnitudes and supporting an antiferromagnetic pairing mechanism.

## Contribution

It provides the first detailed analysis of the two-gap structure in CaFe_{0.88}Co_{0.12}AsF using $H_{c1}^c(T)$ data, advancing understanding of pairing mechanisms in this superconductor.

## Key findings

- Revealed two-gap feature via kink in $H_{c1}^c(T)$ curve
- Determined gap magnitudes: 0.86 meV and 4.48 meV
- Supported antiferromagnetic exchange pairing over Fermi surface nesting

## Abstract

Gap symmetry and structure are crucial issues in understanding the superconducting mechanism of unconventional superconductors. Here we report an in-depth investigation on the out-of-plane lower critical field $H_{c1}^{c}$ of fluorine-based 1111 system superconductor CaFe$_{0.88}$Co$_{0.12}$AsF with $T_c$ = 21 K. A pronounced two-gap feature is revealed by the kink in the temperature dependent $H_{c1}^c(T)$ curve. The magnitudes of the two gaps are determined to be $\Delta_1$ = 0.86 meV and $\Delta_2$ = 4.48 meV, which account for 74% and 26% of the total superfluid density respectively. Our results suggest that the local antiferromagnetic exchange pairing picture is favored compared to the Fermi surface nesting scenario.