Universal Heat Conduction in the Iron Arsenide SuperconductorKFe2As2: Evidence of ad-Wave State

Abstract

The thermal conductivity κ of the iron-arsenide superconductor KFe2As2 was measured down to 50 mK for a heat current parallel and perpendicular to the tetragonal c axis. A residual linear term at T → 0, κ0/T , is observed for both current directions, confirming the presence of nodes in the superconducting gap. Our value of κ0/T in the plane is equal to that reported by Dong et al. [Phys. Rev. Lett. 104, 087005 (2010)] for a sample whose residual resistivity ρ0 was ten times larger. This independence of κ0/T on impurity scattering is the signature of universal heat transport, a property of superconducting states with symmetry-imposed line nodes. This argues against an s-wave state with accidental nodes. It favors instead a d-wave state, an assignment consistent with five additional properties: the magnitude of the critical scattering rate Γc for suppressing Tc to zero; the magnitude of κ0/T , and its dependence on current direction and on magnetic field; the temperature dependence of κ(T ).

Comprehensive scenario for single-crystal growth and doping dependence of resistivity and anisotropic upper critical fields in (Ba1−xKx)FeLiu1, Tanatar2, Straszheim3 et al. 2014Phys. Rev. BSelf Cite6215722View full textAdd to dashboardCite

“…Broad crossover in the temperature-dependent resistivity is observed in in-plane transport in single crystals of BaK122 at doping close to optimal [38], similar to pure stoichiometric KFe 2 As 2 (K122) [39][40][41][42][43]. Explanation of the crossover was suggested as arising from multi-band effects [38], with contribution of two conductivity channels, as found in optical studies [44] with nearly temperature-independent and strongly temperature dependent resistivities, respectively.…”

Angular-dependent upper critical field of overdoped Ba(Fe1−xNix)2Murphy1, Tanatar2, Graf3 et al. 2013Phys. Rev. BSelf Cite235150View full textAdd to dashboardCite

“…The two angular data sets for profoundly multi-band iron pnictide superconductors, slightly underdoped, BaK122, 60 and heavily overdoped K122, 65 generally follow linear dependence despite profound difference in the superconducting gap structure, nodeless in the former case 69 and with vertical line nodes in the latter. 70 Considering that among all the materials for which we were able to find published H c2 (θ), only pure multi-band MgB 2 and NbSe 2 reveal clear deviations from Eq. (1), it is tempting to relate the observed deviations with the multi-band superconductivity in the clean limit.…”

Electronic origin of structural transition in 122 Fe based superconductors

“…It is popularly believed that an anti-s wave (s±) nodal superconducting pairing symmetry [1][2][3] is mediated through the fluctuations associated with the stripe SDW state. This cannot however be valid with certainties to many of the Fe-based superconducting families [4].…”