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Phase fluctuation phenomena in superconductors
KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik, Statistisk fysik.
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2012. , s. ix, 65
Serie
Trita-FYS, ISSN 0280-316X ; 2012:28
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
URN: urn:nbn:se:kth:diva-95464ISBN: 978-91-7501-380-0 (tryckt)OAI: oai:DiVA.org:kth-95464DiVA, id: diva2:528515
Disputation
2012-06-14, FB42, Albanova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning
QC 20120530Tillgänglig från: 2012-05-30 Skapad: 2012-05-25 Senast uppdaterad: 2012-05-30Bibliografiskt granskad
Delarbeten
1. Anomalous Nernst effect and heat transport by vortex vacancies in granular superconductors
Öppna denna publikation i ny flik eller fönster >>Anomalous Nernst effect and heat transport by vortex vacancies in granular superconductors
2010 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, nr 6, s. 060508-1-060508-4Artikel i tidskrift (Refereegranskat) 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.

Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-19261 (URN)10.1103/PhysRevB.81.060508 (DOI)000274998100026 ()2-s2.0-77954832190 (Scopus ID)
Forskningsfinansiär
Vetenskapsrådet
Anmärkning
QC 20100525Tillgänglig från: 2010-08-05 Skapad: 2010-08-05 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
2. Influence of vortices and phase fluctuations on thermoelectric transport properties of superconductors in a magnetic field
Öppna denna publikation i ny flik eller fönster >>Influence of vortices and phase fluctuations on thermoelectric transport properties of superconductors in a magnetic field
2011 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 17, s. 174502-Artikel i tidskrift (Refereegranskat) 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.

Nyckelord
CONTINUOUS SYMMETRY GROUP; LONG-RANGE ORDER; TYPE-2 SUPERCONDUCTORS; 2-DIMENSIONAL SYSTEMS; MIXED-STATE; DESTRUCTION; DYNAMICS; ARRAYS; NERNST
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:kth:diva-33958 (URN)10.1103/PhysRevB.83.174502 (DOI)000290162000004 ()2-s2.0-79961148271 (Scopus ID)
Anmärkning
QC 20110609Tillgänglig från: 2011-06-09 Skapad: 2011-05-23 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
3. Scaling, Finite Size Effects, and Crossovers of the Resistivity and Current-Voltage Characteristics in Two-Dimensional Superconductors
Öppna denna publikation i ny flik eller fönster >>Scaling, Finite Size Effects, and Crossovers of the Resistivity and Current-Voltage Characteristics in Two-Dimensional Superconductors
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
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.

Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:kth:diva-96033 (URN)
Anmärkning
QS 2012Tillgänglig från: 2012-05-30 Skapad: 2012-05-30 Senast uppdaterad: 2012-05-30Bibliografiskt granskad
4. Modeling and simulations of quantum phase slips in ultrathin superconducting wires
Öppna denna publikation i ny flik eller fönster >>Modeling and simulations of quantum phase slips in ultrathin superconducting wires
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:kth:diva-96076 (URN)
Anmärkning
QS 2012Tillgänglig från: 2012-05-30 Skapad: 2012-05-30 Senast uppdaterad: 2012-05-30Bibliografiskt granskad

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