Date of Award
Doctor of Philosophy
Physics and Astronomy
The superconducting gap symmetry of the Fe-based superconductors was studied by measurements and analysis of London penetration depth and superfluid density. Tunnel diode resonator technique for these measurements was implemented in a dilution refrigerator allowing for the temperatures down to 50 mK. For the analysis of the superfluid density, we used both experimental studies of Al-coated samples and original thermodynamic approach based on Rutgers relation. In three systems studied, we found that the superconducting gap at the optimal doping is best described in multi-gap full gap scenario. By performing experiments on samples with artificially introduced disorder with heavy ion irradiation, we show that evolution of the superconducting transition temperature and of the superfluid density are consistent with full-gap sign changing s± superconducting state. The superconducting gap develops strong modulation both in the under-doped and the over-doped regimes. In the terminal hole-doped KFe2As2, both temperature dependence of the superfluid density and its evolution with increase of the scattering rate are consistent with symmetry imposed vertical line nodes in the superconducting gap. By comparative studies of hole-doped (Ba,K)Fe2As2 and electron-doped Ca10-3-8, we show that the superconducting gap modulation in the under-doped regime is intrinsic and is not induced by the coexisting static magnetic order.
Kim, Hyunsoo, "Low temperature London penetration depth and superfluid density in Fe-based superconductors" (2013). Graduate Theses and Dissertations. 13423.