Negative-U superconductivity on the surface of topological insulators
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 10, 104517- p.Article in journal (Refereed) Published
We study the effects of a finite density of negative-U centers (NUCs) on the surface of a three-dimensional topological insulator. The surface Dirac fermions mediate a power-law interaction among the local Cooper pairs at the NUCs, and the interaction remains long-ranged for weak disorder. Superconductivity can be generated in the presence of a random distribution of NUCs. The NUCs play dual roles as both pair creators and pair breakers, and the competition of the two effects results in a nonmonotonic dependence of the mean-field superconducting transition temperature on the density of NUCs. Global phase coherence is established through coupling the locally superconducting puddles via Josephson coupling. Rare fluctuations play important roles, and a globally superconducting phase can only be achieved at large enough concentration of NUCs. The p-wave component of the superconducting order parameter gives rise to frustration among the superconducting grains, which is captured by a Potts-XY type model. New phases with chiral order, glass order, and, possibly, topological order can then emerge in the system of superconducting grains.
Place, publisher, year, edition, pages
2014. Vol. 90, no 10, 104517- p.
IdentifiersURN: urn:nbn:se:su:diva-108533DOI: 10.1103/PhysRevB.90.104517ISI: 000342497200003OAI: oai:DiVA.org:su-108533DiVA: diva2:764644