Strong Pauli-limiting behavior of $H_{c2}$ and uniaxial pressure dependencies in KFe2As2

TL;DR

This study investigates the strong Pauli-limiting effects on the upper critical field in KFe2As2 and explores how uniaxial pressure influences its superconducting and normal-state properties, revealing unique pressure dependencies.

Contribution

It provides detailed thermodynamic analysis of KFe2As2, highlighting its strong Pauli-limiting behavior and distinct pressure effects, which differ from other Fe-based superconductors.

Findings

Strong Pauli-limiting effects for magnetic fields parallel to FeAs planes.

Uniaxial pressure derivatives of $T_c$, $eta_n$, $ ext{susceptibility}$, and $H_c$ calculated.

Doping and pressure relationships in KFe2As2 differ from other Fe-based systems.

Abstract

KFe2As2 single crystals are studied using specific-heat, high-resolution thermal-expansion, magnetization, and magnetostriction measurements. The magnetization and magnetostriction data provide clear evidence for strong Pauli limiting effects for magnetic fields parallel to the FeAs planes, suggesting that KFe2As2 may be a good candidate to search for the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. Using standard thermodynamic relations, the uniaxial pressure derivatives of the critical temperature ($T_{c}$), the normal-state Sommerfeld coefficient ($\gamma_{n}$), the normal-state susceptibility ($\chi$), and the thermodynamic critical field ($H_{c}$) are calculated from our data. We find that the close relationship between doping and pressure as found in other Fe-based systems does not hold for KFe2As2.