טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentZhuravlev Vladimir
SubjectConventional Extremely Type-II Superconductors under Strong
Magnetic Field
DepartmentDepartment of Chemistry
Supervisor Professor Emeritus Tsofar Maniv


Abstract

Type-II superconductors in sufficiently strong magnetic fields exist in a mixed state which has a flux line (vortex) structure. At low temperature vortices form triangular Abrikosov lattice. This periodic space structure of the superconducting order parameter is destroyed by thermal fluctuations, leading to a melting transition of the vortex crystal state at some finite temperature.

In this study an analytical model based on the Ginzburg-Landau theory is developed to describe the fluctuating vortex state in a 2D superconductor. It is shown that the low temperature fluctuations preserve the periodic structure along principal axes of the triangular lattice (chain structure). The model predicts a weak first order melting transition due to rearrangement of the  chain structure caused by thermal destruction of the small phase correlations between any three neighboring chains. In the crystal state the vortex position fluctuations are weak, whereas above the melting point the vortex state is described by  random configurations of the vortex chains.  The parameters of the transition are compared with recent Mote Carlo simulations.

An important part of the study is devoted to the effect of the vortex distribution on the quantum magnetic oscillations. The random vortex configurations corresponding to the vortex “liquid” state just below the superconducting transition lead to a strong quasi particle scattering which suppresses exponentially the amplitude of the de Haas - van Alphen oscillations. In the Abrikosov vortex lattice state the coherent scattering of the quasi particles by the periodic pair potential and the corresponding additional damping are much weaker. In quasi two dimensional superconductors, where phase fluctuation lead to the melting of the vortex lattice  below mean field upper critical field,  vortex freezing should be displayed as a sharp decrease of the slope in the Dingle plot.