Dependence of the absolute value of the penetration depth in (Ba1–x Kx) Fe2 As2 on doping

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Almoalem, Avior
Yagil, Alon
Cho, Kyuil
Teknowijoyo, Serafim
Tanatar, Makariy
Prozorov, Ruslan
Liu, Yong
Auslaender, Ophir
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Lograsso, Thomas
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We report magnetic force microscopy (MFM) measurements on the iron-based superconductor Ba1−xKxFe2As2. By measuring locally the Meissner repulsion with the magnetic MFM tip, we determine the absolute value of the in-plane magnetic penetration depth (λab) in underdoped, optimally doped, and overdoped samples. The results suggest an abrupt increase of λab as doping is increased from xopt, which is potentially related to the presence of a quantum critical point. The response of superconducting vortices to magnetic forces exerted by the MFM tip for x=0.19 and 0.58 is compatible with previously observed structural symmetries at those doping levels.