Strong Pauli-limiting behavior ofHc2and uniaxial pressure dependencies in KFe2As2

Abstract

KFe${}_{2}$As${}_{2}$ 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 of the upper critical field for magnetic fields parallel to the FeAs planes, suggesting that KFe${}_{2}$As${}_{2}$ may be a good candidate to search for the Fulde-Ferrell-Larkin-Ovchinnikov state. Using standard thermodynamic relations, the uniaxial pressure derivatives of the critical temperature ${T}_{c}$, the normal-state Sommerfeld coefficient ${\ensuremath{\gamma}}_{n}$, the normal-state susceptibility $\ensuremath{\chi}$, 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 KFe${}_{2}$As${}_{2}$.