| Abstract: | We present Magnetic Force Microscopy (MFM) measurements of the hole-doped iron-based superconductor (Ba1-xKx)Fe2As2 across the superconducting dome. We making use of the Meissner effect to measure the magnetic penetration depth (λ) as a function of doping (x). This reveals a possible new feature in the dependence of λ on x: an abrupt change near optimal doping. This change seems to coincide with the onset of a gap closing and the disappearing of an electron pocket from the band structure, as revealed by previous ARPES measurements. In addition, MFM vortex imaging and manipulation enable us to map defects and learn about the pinning landscape. The way vortices move suggests broken crystal symmetry on the underdoped side which suggests the orthorhombic phase measured in other studies. On the overdoped side we measure isotropic vortex motion that suggests a tetragonal crystal structure. |
