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The dependence of the absolute value penetration depth on doping in (Ba1−xKx)Fe2As2
Avior Almoalem [1] , Alon Yagil [1] , Kyuil Cho [2,3] , Serafim Teknowijoyo [2,3] , Makariy A. Tanatar [2,3] , Ruslan Prozorov [2,3] , Yong Liu [2] , Thomas A. Lograsso [2,4] , Ophir M. Auslaender [1]
[1] Department of Physics, Technion - Israel Institute of Technology
[2] Ames Laboratory, Ames
[3] Department of Physics and Astronomy, Iowa State University, Ames
[4] Department of Materials Science and Engineering, Iowa State University, Ames
We report magnetic force microscopy (MFM) measurements on the hole-doped iron-based superconductor Ba1-xKxFe2As2. By locally measuring the Meissner repulsion of the magnetic MFM tip we extract the in-plane magnetic penetration depth λab in underdoped (0.19<x<0.34), optimally-doped (xOPT = 0.34 ), and overdoped samples (0.34<x<0.58). This provides information on the superconducting phase, as λab is a measure of the superfluid density (ρS ∝ λ-2ab). Previous measurements of λab in closely related materials have shown both a minimum near (Ba(Fe1-xCox)2As2 [1]) and a peak (BaFe2(As1-xPx)2[2]). Our results show an abrupt increase of λab as doping is increased from xOPT. Additional measurements in the overdoped regime suggest an increase of both the effective mass and the pairing energy. Our results, combined with previous studies, indicate the presence of a new phase which reduces ρS and affects the effective mass by changing the particle-particle interactions in the overdoped regime.
[1] Lan Luan, T. M. Lippman, C. W. Hicks, J. A. Bert, O. M. Auslaender, J.-H. Chu, J. G. Analytis, I. R. Fisher, and K. A. Moler, Local measurement of the superfluid density in the pnictide superconductor Ba(Fe1-xCox)2As2 across the superconducting dome, Phys. Rev. Lett. 106, 067001 (2011).
[2] Y. Lamhot, A. Yagil, N. Shapira, S. Kasahara, T. Watashige, T. Shibauchi, Y. Matsuda, and O. M. Auslaender, Local characterization of superconductivity in BaFe2(As1-xPx)2, Phys. Rev. B 91, 060504 (2015).