title: Pauli-limited multiband superconductivity in KFe2As2.
abstract: The upper critical field H(c2)(T) of the multiband superconductor KFe2As2 has been studied via low-temperature thermal expansion and magnetostriction measurements. We present compelling evidence for Pauli-limiting effects dominating H(c2)(T) for H || a, as revealed by a crossover from second- to first-order phase transitions to the superconducting state in the magnetostriction measurements down to 50 mK. Corresponding features were absent for H || c. To our knowledge, this crossover constitutes the first confirmation of Pauli limiting of the H(c2)(T) of a multiband superconductor. The results are supported by modeling Pauli limits for single-band and multiband cases.
authors: Institute for Solid State Physics, IFP, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany. diego.zocco@kit.edu
authors: D A
authors: DA
authors: Zocco
authors: K
authors: K
authors: Grube
authors: F
authors: F
authors: Eilers
authors: T
authors: T
authors: Wolf
authors: H V
authors: HV
authors: Löhneysen