2020/12/01 by Indranil Roy, Roy, Indranil
Physics and Astronomy · #Physics of Superconductivity and Magnetism
paper · pdf · doi:10.48550/arxiv.2012.00709
The work reported in my doctoral thesis is an experimental study of vortex\ndynamics and phase transitions in thin films of type II superconductors using\nscanning tunneling spectroscopy, low frequency ac susceptibility measurements\nand complimentary transport measurements. Chapter I and II cover basics of\nsuperconductivity and methodologies used in the thesis. Chapter III discusses\nthe effect of periodic pinning centers on the geometry and dynamics of vortex\nlattice in NbN thin films. Consequent study of dynamic transition of vortex\nMott-like to vortex metal-like state is described. In Chapter IV, effect of\nstrong disorder on vortex lattice in NbN thin films is studied. Here we show\nmagnetic field induced granularity gives rise to pseudogap phase which is\nutilized to explain superconductor to insulator-like transition in stronger\ndisorder. Chapter V contains the study of 2-dimensional vortex lattice melting\nin a-MoGe thin films. We discuss the observation of hexatic vortex fluid phase\nand the BKTHNY two-step melting in this scenario. Effect of sample thickness on\nthis phases is also described. In Chapter VI, we study the possibility of\nquantum fluctuation of vortices in weakly pinned a-MoGe thin films. Effect of\npinning on this fluctuation and a possibility of a quantum to thermal crossover\nis also explored.\n