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Phase fluctuation phenomena in superconductors
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , ix, 65 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:28
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-95464ISBN: 978-91-7501-380-0 (print)OAI: oai:DiVA.org:kth-95464DiVA: diva2:528515
Public defence
2012-06-14, FB42, Albanova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120530Available from: 2012-05-30 Created: 2012-05-25 Last updated: 2012-05-30Bibliographically approved
List of papers
1. Anomalous Nernst effect and heat transport by vortex vacancies in granular superconductors
Open this publication in new window or tab >>Anomalous Nernst effect and heat transport by vortex vacancies in granular superconductors
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 6, 060508-1-060508-4 p.Article in journal (Refereed) Published
Abstract [en]

We study the Nernst effect due to vortex motion in two-dimensional granular superconductors using simulations with Langevin or resistively shunted Josephson-junction dynamics. In particular, we show that the geometric frustration of both regular and irregular granular materials can lead to thermally driven transport of vortices from colder to hotter regions, resulting in a sign reversal of the Nernst signal. We discuss the underlying mechanisms of this anomalous behavior in terms of heat transport by mobile vacancies in an otherwise pinned vortex lattice.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-19261 (URN)10.1103/PhysRevB.81.060508 (DOI)000274998100026 ()2-s2.0-77954832190 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Influence of vortices and phase fluctuations on thermoelectric transport properties of superconductors in a magnetic field
Open this publication in new window or tab >>Influence of vortices and phase fluctuations on thermoelectric transport properties of superconductors in a magnetic field
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 17, 174502- p.Article in journal (Refereed) Published
Abstract [en]

We study heat transport and thermoelectric effects in two-dimensional superconductors in a magnetic field. These are modeled as granular Josephson-junction arrays, forming either regular or random lattices. We employ two different models for the dynamics: relaxational model-A dynamics or resistively and capacitively shunted Josephson junction dynamics. We derive expressions for the heat current in these models, which are then used in numerical simulations to calculate the heat conductivity and Nernst coefficient for different temperatures and magnetic fields. At low temperatures and zero magnetic field the heat conductivity in the RCSJ model is calculated analytically from a spin wave approximation, and is seen to have an anomalous logarithmic dependence on the system size, and also to diverge in the completely overdamped limit C -> 0. From our simulations we find at low magnetic fields that the Nernst signal displays a characteristic "tilted hill" profile similar to experiments and a nonmonotonic temperature dependence of the heat conductivity. We also investigate the effects of granularity and randomness, which become important for higher magnetic fields. In this regime geometric frustration strongly influences the results in both regular and random systems and leads to highly nontrivial magnetic field dependencies of the studied transport coefficients.

Keyword
CONTINUOUS SYMMETRY GROUP; LONG-RANGE ORDER; TYPE-2 SUPERCONDUCTORS; 2-DIMENSIONAL SYSTEMS; MIXED-STATE; DESTRUCTION; DYNAMICS; ARRAYS; NERNST
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-33958 (URN)10.1103/PhysRevB.83.174502 (DOI)000290162000004 ()2-s2.0-79961148271 (Scopus ID)
Note
QC 20110609Available from: 2011-06-09 Created: 2011-05-23 Last updated: 2017-12-11Bibliographically approved
3. Scaling, Finite Size Effects, and Crossovers of the Resistivity and Current-Voltage Characteristics in Two-Dimensional Superconductors
Open this publication in new window or tab >>Scaling, Finite Size Effects, and Crossovers of the Resistivity and Current-Voltage Characteristics in Two-Dimensional Superconductors
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We revisit the scaling properties of the resistivity and the current-voltage characteristics at and below the Berezinskii-Kosterlitz-Thouless transition, both in zero and nonzero magnetic field. The scaling properties are derived by integrating the renormalization group flow equations up to a scale where they can be reliably matched to simple analytic expressions. The vortex fugacity turns out to be dangerously irrelevant for these quantities below $T_c$, thereby altering the scaling behavior. We derive the possible crossover effects as the current, magnetic field or system size is varied, and find a strong multiplicative logarithmic correction near $T_c$, all which is necessary to account for when interpreting experiments and simulation data. Our analysis clarifies a longstanding discrepancy between the finite size dependence found in many simulations and the current-voltage characteristics of experiments. We further show that the logarithmic correction can be avoided by approaching the transition in a magnetic field, thereby simplifying the scaling analysis. We confirm our results by large scale numerical simulations, and calculate the dynamic critical exponent $z$, for relaxational Langevin dynamics and for resistively and capacitively shunted Josephson junction dynamics.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-96033 (URN)
Note
QS 2012Available from: 2012-05-30 Created: 2012-05-30 Last updated: 2012-05-30Bibliographically approved
4. Modeling and simulations of quantum phase slips in ultrathin superconducting wires
Open this publication in new window or tab >>Modeling and simulations of quantum phase slips in ultrathin superconducting wires
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-96076 (URN)
Note
QS 2012Available from: 2012-05-30 Created: 2012-05-30 Last updated: 2012-05-30Bibliographically approved

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