Thermodynamic Study of Nodal Structure and Multiband Superconductivity of KFe^sub 2^As^sub 2

The temperature, field, and field-orientation dependences of the electronic specific heat C... of the iron-pnictide superconductor KFe...As... have been investigated. Thermodynamic evidence of the presence of line nodes is obtained from the T and \(\sqrt{H} \) linear dependences of C.../T in the low-T and low-H region. Under a magnetic field rotated within the tetragonal ab-plane, a fourfold oscillation is observed in C... with a sign change at 0.08T... On the basis of the Doppler-shift analysis, the observed C... minima in H || [100] at low T indicate the presence of line nodes somewhere on the Fermi surface where the Fermi velocity is parallel to the [100] direction; this is consistent with the octet-line-node scenario proposed recently by a photoemission experiment. In addition, the low-T C.../T exhibits an unusual upturn on cooling at moderate fields only for H || ab, which is understood in terms of the strong Pauli paramagnetic effect on multiband superconductivity. (ProQuest: ... denotes formulae/symbols omitted.)