Evolution of London penetration depth with scattering in single crystals of K1−x Nax

H. Kim

¹

,

M. A. Tanatar

²

,

Yong Liu

³

et al.

Abstract

London penetration depth, λ(T ), was measured in single crystals of K 1−x Na x Fe 2 As 2 , x = 0 and 0.07, down to temperatures of 50 mK, ∼ T c /50. Isovalent substitution of Na for K significantly increases impurity scattering, with ρ(T c ) rising from 0.2 to 2.2 μ cm, and leads to a suppression of T c from 3.5 to 2.8 K. At the same time, a close to T -linear λ(T ) in pure samples changes to almost T 2 in the substituted samples. The behavior never becomes exponential as expected for the accidental nodes, as opposed to T 2 dependence in superconductors with symmetry imposed line nodes. The superfluid density in the full temperature range follows a simple clean and dirty d-wave dependence, for pure and substituted samples, respectively. This result contradicts suggestions of multiband scenarios with strongly different gap structure on four sheets of the Fermi surface.

Orbital and Pauli limiting effects in heavily dopedBa0.05K0.95Fe2As2

“…Furthermore, laser-excited angle-resolved photoemission spectroscopy measurements 12 have revealed a highly unusual gap structure in KFe 2 As 2 with octet-line nodes on the middle hole Fermi sheet and nodeless gaps on inner and outer Fermi surfaces. In addition, while ARPES 12,24,25 , residual thermal conductivity 14 , and specific heat [26][27][28] results support an accidental nodes scenario, thermal conductivity 29,30 and measurements of the changes in the superconducting critical temperature with pressure P in KFe 2 As 2 13 , which reveal an evolution from a d-wave gap for P < P c to a s ± gap for P > P c , strongly support a symmetry protected nodes scenario; impurity scattering effect studied using thermal conductivity 29 , London penetration depth 31 , and specific heat 32 measurements also supports the scenario of symmetry-protected line nodes. Thus, the gap symmetry with nodes in this system is still an open question.…”

Unexpected impact of magnetic disorder on multiband superconductivity

“…Qualitatively these results were confirmed via the numerical solutions of the Bogoliubovde Gennes equations 14,15 . Several experiments show that the T c suppression is much weaker than expected in the framework of the AG theory for both non-magnetic [16][17][18][19][20][21] and magnetic disorder 16,[22][23][24][25] . Overall, there is no clear answer to whether the sign-changing order parameter symmetry is prevailing in FeBS.…”

Superconducting properties ofK1−xNaxFe2As2under pressure

“…10 However, in the present case the nature and the strength of these correlation effects as well as the symmetry of the superconducting order parameter are still under debate. Some experiments were interpreted in favor of s ± -wave SC with accidental nodes 9,11-13 whereas other favor d-wave SC 5,7,8,14,15 . Based on their theoretical calculations the authors of Ref.…”