Ginzburg-Landau theory of transport properties and fluctuations in Type-II superconductors

• Main Authors: Bui, Duc Tinh, 卜德廷
• Other Authors: Rosenstein, Baruch
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/01091803119012034230

博士 === 國立交通大學 === 電子物理系所 === 99 === The discovery of high-temperature superconductors (HTSC) has revived interest in thermal fuctuation effects in superconductors, both in thermodynamic properties and in transport properties, with emphasis on the heat transport. In this work we shall be concerned with the effect of fuctuations on the transport properties of a superconductor in a magnetic field. Under the influence of fuctuations at high temperature, the motions of vortices are responsible for the thermodynamic properties and transport properties of systems especially for those unconventional superconductors due to it's strong anisotropic magnetic properties. The Ginzburg-Landau (GL) phenomenological description of high superconductors has been remarkably successful in describing various thermodynamic and transport properties. In the mean field approximation, when the fuctuations are neglected, it is relatively simple. However when fuctuations are not negligible, even this effective description becomes very complicated. Some progress can be achieved when certain additional assumptions are added. An additional assumption, often made in analytical calculations, is that only the lowest Landau level significantly contributes to physical quantities of interest. However, in a large domain of external parameters (magnetic field, temperature) currently under experimental investigation, this approximation is not valid and now there is a need to generalize the theory to include all Landau levels. In the past only electric transport has been thoroughly developed theoretically. However recent experimental advance in observing various magnetocaloric coefficient and heat transport phenomena like the Nernst and thermoelectric power necessitate extension of the fuctuations theory to include these phenomena. When only the Gaussian fuctuations are considered, then the thermoelectric conductivity and the electrical conductivity were predicted to diverge at the mean-field transition temperature, in conflict with the experimental results. One of important conclusions is that interactions between the fluctuations must be considered in order to obtain even qualitative agreement with the experimental results. An early work on this subject was application of the Hartree-Fock approximation to treat the quartic term within the lowest Landau level approximation in the GL Hamiltonian for heat transport current by S. Ullah and A. T. Dorsey. In this thesis I have extended the work to include all Landau level, use more systematic Gaussian approximation and calculate physical quantities of current interest like the transverse thermoelectric conductivity and the Nernst signal, describing the Nernst effect, as well as ac conductivity in linear response in Type-II superconductor in the vortex-liquid regime. The time-dependent Ginzburg-Landau (TDGL) equation with thermal noise is used. Our results show a good agreement with several experiment and numerical simulation on HTSC. I also studied the transport properties in a layered Type-II superconductor under magnetic field beyond the linear response. By using TDGL equation with thermal noise is to obtain electrical conductivity and Hall conductivity. Our results are in good qualitative and even qualitative agreement with experimental data on HTSC in strong electric fields.