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Phase transitions with critical loop disorder
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.ORCID iD: 0000-0003-1164-0831
(English)Manuscript (preprint) (Other academic)
##### National Category
Physical Sciences
##### Identifiers
OAI: oai:DiVA.org:kth-160965DiVA, id: diva2:793050
##### Note

QS 2015

Available from: 2015-03-06 Created: 2015-03-06 Last updated: 2015-03-06Bibliographically approved
##### In thesis
1. Phase transitions in novel superfluids and systems with correlated disorder
Open this publication in new window or tab >>Phase transitions in novel superfluids and systems with correlated disorder
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
##### Abstract [en]

Condensed matter systems undergoing phase transitions rarely allow exact solutions. The presence of disorder renders the situation  even worse but collective Monte Carlo methods and parallel algorithms allow numerical descriptions. This thesis considers classical phase transitions in disordered spin systems in general and in effective models of superfluids with disorder and novel interactions in particular. Quantum phase transitions are considered via a quantum to classical mapping. Central questions are if the presence of defects changes universal properties and what qualitative implications follow for experiments. Common to the cases considered is that the disorder maps out correlated structures. All results are obtained using large-scale Monte Carlo simulations of effective models capturing the relevant degrees of freedom at the transition.

Considering a model system for superflow aided by a defect network, we find that the onset properties are significantly altered compared to the $\lambda$-transition in $^{4}$He. This has qualitative implications on expected experimental signatures in a defect supersolid scenario.

For the Bose glass to superfluid quantum phase transition in 2D we determine the quantum correlation time by an anisotropic finite size scaling approach. Without a priori assumptions on critical parameters, we find the critical exponent $z=1.8 \pm 0.05$ contradicting the long standing result $z=d$.

Using a 3D effective model for multi-band type-1.5 superconductors we find that these systems possibly feature a strong first order vortex-driven phase transition. Despite its short-range nature details of the interaction are shown to play an important role.

Phase transitions in disordered spin models exposed to correlated defect structures obtained via rapid quenches of critical loop and spin models are investigated. On long length scales the correlations are shown to decay algebraically. The decay exponents are expressed through known critical exponents of the disorder generating models. For cases where the disorder correlations imply the existence of a new long-range-disorder fixed point we determine the critical exponents of the disordered systems via finite size scaling methods of Monte Carlo data and find good agreement with theoretical expectations.

##### Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. 12, 111
##### Series
TRITA-FYS, ISSN 0280-316X ; 2015:09
##### Keyword
condensed matter physics, phase transitions, critical phenomena, spin models, quantum phase transitions, quantum fluids, superfluidity, superconductivity, disordered systems, Bose glass, dirty bosons, vortex pinning, statistical mechanics, Monte Carlo simulation, Wolff algorithm, classical worm algorithm, Wang-Landau algorithm
##### National Category
Condensed Matter Physics
Physics
##### Identifiers
urn:nbn:se:kth:diva-160929 (URN)978-91-7595-467-7 (ISBN)
##### Public defence
2015-03-27, sal FB42, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
##### Note

QC 20150306

Available from: 2015-03-06 Created: 2015-03-04 Last updated: 2016-12-06Bibliographically approved

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Wallin, Mats

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