Browsing by Author "Tinh, Bui Duc"

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Electrical conductivity beyond a linear response in layered superconductors under a magnetic field
(2010-06-29)
Tinh, Bui Duc
;
Li, Dingping
;
Rosenstein, Baruch
;
電子物理學系
;
Department of Electrophysics
The time-dependent Ginzburg-Landau approach is used to investigate nonlinear response of a strongly type-II superconductor. The dissipation takes a form of the flux flow which is quantitatively studied beyond linear response. Thermal fluctuations, represented by the Langevin white noise, are assumed to be strong enough to melt the Abrikosov vortex lattice created by the magnetic field into a moving vortex liquid and marginalize the effects of the vortex pinning by inhomogeneities. The layered structure of the superconductor is accounted for by means of the Lawrence-Doniach model. The nonlinear interaction term in dynamics is treated within self-consistent Gaussian approximation and we go beyond the often used lowest Landau level approximation to treat arbitrary magnetic fields. The I-V curve is calculated for arbitrary temperature and the results are compared to experimental data on high-T-c. superconductor YBa2Cu3O7-delta.
Theory of Nernst effect in high-T(c) superconductors
(2009-01-01)
Tinh, Bui Duc
;
Rosenstein, Baruch
;
電子物理學系
;
Department of Electrophysics
We calculated, using the time-dependent Ginzburg-Landau equation with thermal noise, the transverse thermoelectric conductivity alpha(xy) and the Nernst signal e(N), describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree-Fock utilized by Ullah and Dorsey [Phys. Rev. Lett. 65, 2066 (1990)]. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The resulting values in two dimensions are significantly lower than the numerical simulation data of the same model but are in reasonably good quantitative agreement with experimental data on La(2)SrCuO(4) above the irreversibility line (below the irreversibility line at which alpha(xy) diverges and theory should be modified by including pinning effects). The values of e(N) calculated in three dimensions are also in good quantitative agreement with experimental data for temperature close to T(c) on YBa(2)Cu(3)O(7). For each of the materials we consider, the melting and the irreversibility lines are also fitted with the same set of parameters using a recent quantitative Ginzburg-Landau theory.
Theory of Nernst effect in high-T-c superconductors
(2009-01-01)
Tinh, Bui Duc
;
Rosenstein, Baruch
;
電子物理學系
;
Department of Electrophysics
We calculated, using the time-dependent Ginzburg-Landau equation with thermal noise, the transverse thermoelectric conductivity alpha(xy) and the Nernst signal e(N), describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The Gaussian method used is an elaboration of the Hartree-Fock utilized by Ullah and Dorsey [Phys. Rev. Lett. 65, 2066 (1990)]. An additional assumption often made in analytical calculations that only the lowest Landau level significantly contributes to physical quantities of interest in the high-field limit is lifted by including all the Landau levels. The resulting values in two dimensions are significantly lower than the numerical simulation data of the same model but are in reasonably good quantitative agreement with experimental data on La2SrCuO4 above the irreversibility line (below the irreversibility line at which alpha(xy) diverges and theory should be modified by including pinning effects). The values of e(N) calculated in three dimensions are also in good quantitative agreement with experimental data for temperature close to T-c on YBa2Cu3O7. For each of the materials we consider, the melting and the irreversibility lines are also fitted with the same set of parameters using a recent quantitative Ginzburg-Landau theory.