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Dissipative quantum phase transitions and high-temperature superconductorsPrimeFaces.cw("AccordionPanel","widget_formSmash_some",{id:"formSmash:some",widgetVar:"widget_formSmash_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_all",{id:"formSmash:all",widgetVar:"widget_formSmash_all",multiple:true});
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PrimeFaces.cw("AccordionPanel","widget_formSmash_responsibleOrgs",{id:"formSmash:responsibleOrgs",widgetVar:"widget_formSmash_responsibleOrgs",multiple:true}); 2012 (English)Doctoral thesis, comprehensive summary (Other academic)
##### Abstract [en]

##### Place, publisher, year, edition, pages

NTNU, 2012.
##### Series

Doctoral theses at NTNU, ISSN 1503-8181 ; 2012:229
##### National Category

Physics
##### Identifiers

URN: urn:nbn:no:ntnu:diva-17523ISBN: 978-82-471-3760-4 (printed ver.)ISBN: 978-82-471-3761-1 (electronic ver.)OAI: oai:DiVA.org:ntnu-17523DiVA: diva2:559413
##### Public defence

2012-09-12, 00:00
#####

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Available from: 2012-10-09 Created: 2012-10-09 Last updated: 2012-10-10Bibliographically approved
##### List of papers

This thesis presents seven research papers on topics in condensed-matter theory. Five of the papers report on Monte Carlo studies of quantum phase transitions in various (*d*+1)-dimensional statistical mechanics models featuring Caldeira-Leggettlike dissipation. The principal motivation for these studies was to investigate a particular bond-dissipative (2+1)-dimensional *XY* model of circulating currents in cuprate high-temperature superconductors. It has been proposed that quantum critical fluctuations associated with a local quantum critical point described by this model can explain the marginal-Fermi-liquid behaviour of the normal state of these compounds. We present simulation results for this model for both compact and noncompact phase variables and show unambiguously that the quantum critical point in the compact case is not local. If the phases are taken to be noncompact variables, the model is also a model of resistively shunted Josephson junction arrays. The results in this case reveal a more complicated phase diagram, but we have not been able to establish critical behaviour consistent with the scenario of local quantum criticality.

The study of extended quantum dissipative models is also motivated by the general effect on condensed-matter systems of the coupling to environmental degrees of freedom. Their influence on quantum critical phenomena is characterized by the dynamical critical exponent *z*, a measure of spatiotemporal anisotropy, the value of which can be estimated by naive scaling arguments. We confirm by numerical means that such scaling estimates give correct results to a good approximations (with a few reservations), irrespective of system dimensionality, order parameter symmetry, or whether the variables are compact or noncompact. Corrections to the naive scaling estimates have to be invoked for strongly super-Ohmic dissipation for *d* = 1 due to relatively large values of the anomalous scaling dimension *η*.

The two last research papers are concerned with the superconducting pairing state of the recently discovered class of iron-based high-temperature superconductors. Here, we calculate possible signatures of the proposed *s*±-wave pairing state in conductance-spectroscopy and Josephson-effect experiments.

1. Monte Carlo simulations of dissipative quantum Ising models$(function(){PrimeFaces.cw("OverlayPanel","overlay555829",{id:"formSmash:j_idt432:0:j_idt436",widgetVar:"overlay555829",target:"formSmash:j_idt432:0:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

2. Quantum criticality in spin chains with non-Ohmic dissipation$(function(){PrimeFaces.cw("OverlayPanel","overlay555863",{id:"formSmash:j_idt432:1:j_idt436",widgetVar:"overlay555863",target:"formSmash:j_idt432:1:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

3. Criticality of compact and noncompact quantum dissipative Z(4) models in (1+1) dimensions$(function(){PrimeFaces.cw("OverlayPanel","overlay555833",{id:"formSmash:j_idt432:2:j_idt436",widgetVar:"overlay555833",target:"formSmash:j_idt432:2:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

4. Quantum criticality in a dissipative (2+1)-dimensional XY model of circulating currents in high-T-c cuprates$(function(){PrimeFaces.cw("OverlayPanel","overlay555831",{id:"formSmash:j_idt432:3:j_idt436",widgetVar:"overlay555831",target:"formSmash:j_idt432:3:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

5. Three distinct types of quantum phase transitions in a (2+1)-dimensional array of dissipative Josephson junctions$(function(){PrimeFaces.cw("OverlayPanel","overlay555830",{id:"formSmash:j_idt432:4:j_idt436",widgetVar:"overlay555830",target:"formSmash:j_idt432:4:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

6. 0-pi phase shifts in Josephson junctions as a signature for the s(+/-)-wave pairing state$(function(){PrimeFaces.cw("OverlayPanel","overlay559526",{id:"formSmash:j_idt432:5:j_idt436",widgetVar:"overlay559526",target:"formSmash:j_idt432:5:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

7. Quantum transport in ballistic s(+/-)-wave superconductors with interband coupling: Conductance spectra, crossed Andreev reflection, and Josephson current$(function(){PrimeFaces.cw("OverlayPanel","overlay559525",{id:"formSmash:j_idt432:6:j_idt436",widgetVar:"overlay559525",target:"formSmash:j_idt432:6:partsLink",showEvent:"mousedown",hideEvent:"mousedown",showEffect:"blind",hideEffect:"fade",appendToBody:true});});

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