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Characteristic properties of two-dimensional superconductors close to the phase transition in zero magnetic field
Umeå University, Faculty of Science and Technology, Physics.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis lies on the critical properties of twodimensional (2D) superconductors in zero magnetic field. Simulations based on variants of the 2D XY model are shown to give characteristic features close to the phase transition which agree qualitatively with experimental data. Thus, it is concluded that these common characteristic features are caused by two-dimensional vortices.

The thesis consists of an introductory part and five separate publications. In the introductory part of the thesis the basic results of the Ginzburg-Landau model, which gives a phenomenological description of superconductors, are described. In 2D systems, the superconductive phase transition in the absence of a magnetic field is governed by the unbinding of thermally created vortices and is called the Kosterlitz-Thouless (KT) phase transition. An introduction to this kind of transition is given. The important features of the current-voltage (IV) characteristics and the nonlinear conductivity, which can be used to study the KT transition, are discussed. The scaling analysis procedure, a powerful tool for the analysis of the properties of a system in the vicinity of phase transition, is reviewed. A scaling form for the nonlinear dc conductivity, which takes into account finite-size e ects, is discussed.

The static 2D XY model, which is usually used to describe superfluids, superconducting films as well as the high-Tc superconductors with high anisotropy, is introduced. Three different types of dynamic models, namely resistively shunted junction, relaxational, and Monte Carlo dynamics are superimposed on the 2D XY model for the evaluation of the dynamic properties. TheVillain model and a modifiedXY model using a p-type interaction potential exhibit different densities of the thermally created vortices. Since the dominant characteristic physical features close to the KT transition are associated with vortex pair fluctuations these two models are investigated.

The introductory part closes with a short introduction to each of the five published articles.

Place, publisher, year, edition, pages
2003. , 62 p.
Keyword [en]
Physics
Keyword [sv]
Fysik, superconductor, two dimensions, phase transition, vortex, currentvoltage characteristics, complex conductivity, scaling, critical exponents, XY-type models, dynamics
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-102ISBN: 91-7305-490-9 (print)OAI: oai:DiVA.org:umu-102DiVA: diva2:139987
Public defence
2003-10-03, Umeå, 10:00
Available from: 2003-09-15 Created: 2003-09-15Bibliographically approved
List of papers
1. Analysis of current-voltage characteristics of two-dimensional superconductors: Finite-size scaling behavior in the vicinity of the Kosterlitz-Thouless transition
Open this publication in new window or tab >>Analysis of current-voltage characteristics of two-dimensional superconductors: Finite-size scaling behavior in the vicinity of the Kosterlitz-Thouless transition
2000 In: Physical Review B, Vol. 62, no 21, 14531–14540- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2141 (URN)
Available from: 2003-09-15 Created: 2003-09-15Bibliographically approved
2. Ubiquitous finite-size scaling features in I-V characteristics of various dynamic XY models in two dimensions
Open this publication in new window or tab >>Ubiquitous finite-size scaling features in I-V characteristics of various dynamic XY models in two dimensions
2001 In: Physica C: Superconductivity, Vol. 355, no 1-2, 6-14 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2142 (URN)
Available from: 2003-09-15 Created: 2003-09-15Bibliographically approved
3. Splitting of the superconducting transition in the two weakly coupled 2D XY models
Open this publication in new window or tab >>Splitting of the superconducting transition in the two weakly coupled 2D XY models
2002 In: Physica C: Superconductivity, Vol. 369, no 1-4, 282-285 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2143 (URN)
Available from: 2003-09-15 Created: 2003-09-15Bibliographically approved
4. Comment on "Loss of superconducting phase coherence in YBa2Cu3O7 films: vortex-loop unbinding and Kosterlitz-Thouless phenomena"
Open this publication in new window or tab >>Comment on "Loss of superconducting phase coherence in YBa2Cu3O7 films: vortex-loop unbinding and Kosterlitz-Thouless phenomena"
2002 In: Physical Review Letters, Vol. 89, 149703- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2144 (URN)
Available from: 2003-09-15 Created: 2003-09-15Bibliographically approved
5. Dynamic critical behavior of the XY model in small-world networks
Open this publication in new window or tab >>Dynamic critical behavior of the XY model in small-world networks
2003 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 67, no 3, 036118- p.Article in journal (Refereed) Published
Abstract [en]

The critical behavior of the XY model on small-world network is investigated by means of dynamic Monte Carlo simulations. We use the short-time relaxation scheme, i.e., the critical behavior is studied from the nonequilibrium relaxation to equilibrium. Static and dynamic critical exponents are extracted through the use of the dynamic finite-size scaling analysis. It is concluded that the dynamic universality class at the transition is of the mean-field nature. We also confirm numerically that the value of dynamic critical exponent is independent of the rewiring probability P for P≳0.03.

Place, publisher, year, edition, pages
American Physical Society, 2003
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-2145 (URN)10.1103/PhysRevE.67.036118 (DOI)
Available from: 2003-09-15 Created: 2003-09-15 Last updated: 2017-12-14Bibliographically approved

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