טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAvior Almoalem
SubjectLocal measurement of the penetration depth across the
superconducting dome in (Ba1-xKx)Fe2As2
DepartmentDepartment of Physics
Supervisor Dr. Auslaender Ophir
Full Thesis textFull thesis text - English Version


Abstract

I present magnetic force microscopy (MFM) measurements of the hole-doped iron-based superconductor (Ba1-xKx)Fe2As2 across the superconducting dome. Single crystals of  (Ba1-xKx)Fe2As2 have only recently been grown with high quality. This is important because the hole doping in (Ba1-xKx)Fe2As2 occurs by substitution away from the Fe-As planes. Consequently (Ba1-xKx)Fe2As2 is potentially less disordered than other members of its pnictide family. (Ba1-xKx)Fe2As2 exhibits a different superconducting behavior from other members of the iron-based superconductors, as well as new phases. I make use of the Meissner effect to measure the magnetic penetration depth λab as a function of doping (x). The measurements reveal a possible new feature in the dependence of magnetic penetration depth on doping: an abrupt change near optimal doping, on the overdoped side. This abrupt change seems to coincide with a change of the band structure, as revealed by previous measurements. In addition, we use the magnetic force microscope for vortex imaging and manipulation. Imaging and manipulation allows us to map defects and to acquire information about the pinning landscape in the samples. The way vortices move through the samples is consistent with broken structural symmetry on the underdoped side. This suggests the orthorhombic phase measured previously. On the overdoped side our measurements are consistent with a tetragonal crystal structure.