KFe2As2: coexistence of superconductivity and local moment derived spin-glass

TL;DR

This study investigates KFe2As2 single crystals, revealing the coexistence of superconductivity with disordered magnetic phases like spin-glass, influenced by local magnetic moments and sample inhomogeneity, and provides a phenomenological explanation for their electronic behavior.

Contribution

It offers a new phenomenological model explaining the coexistence of superconductivity and magnetic disorder in KFe2As2, linking local moments to non-Fermi-liquid behavior and specific heat anomalies.

Findings

Superconductivity coexists with spin-glass and Griffiths magnetic phases.

The intrinsic Sommerfeld coefficient gamma_el is about 60 mJ/mol K^2.

The electron-boson coupling constant lambda is approximately 1.

Abstract

High-quality KFe2As2 single crystals have been studied by transport, magnetization and low-T specific heat measurements. Their analysis shows that superconductivity occurs (in some cases coexists) in the vicinity of disordered magnetic phases (Griffiths and spin-glass type) depending of the amount of local magnetic moments (probably excess Fe derived)and sample inhomogeneity. The achieved phenomenological description of our data including also data from the literature provides a consistent explanation of the observed non-Fermi-liquid behavior and of the nominally large experimental Sommerfeld coefficient gamma_n about 94 mJ/mol K^2. We suggest that the intrinsic value (directly related to the itinerant quasi-particles) gamma_el about 60(10)mJ/mol K^2 is significantly reduced compared with gamma_n. Then an enhanced relative jump of the electronic specific heat Delta C_el/gamma_el T_c about 0.8 and a weak total electron-boson coupling constant lambda less or about 1 follow.