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

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 (${\hat{I}}_n^3$), the normal-state susceptibility ($\ddot{I}‡$), 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.