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Global critical temperature in disordered superconductors with weak multifractality


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Authors

Mayoh, J 
García-García, AM 

Abstract

There is growing evidence, from experiments and numerical simulations, that a key feature of sufficiently disordered superconductors is the spatial inhomogeneity of the order parameter. However not much is known analytically about the details of its spatial distribution or the associated global critical temperature that signals the breaking of long-range order. Here we address this problem for disordered systems around an Anderson transition characterized by multifractal one-body eigenstates. In the limit of weak multifractality and for weakly coupled superconductors we compute the superconducting order parameter analytically, including its energy dependence and statistical distribution in space. The spatial distribution of the order parameter is found to be always log-normal. The global critical temperature, computed by percolation techniques and neglecting phase fluctuations, is enhanced with respect to the clean limit only for very weakly coupled superconductors. Some enhancement still persists even in the presence of moderate phase fluctuations crudely modelled by increasing the percolation threshold. Our results are also consistent with experiments, where enhancement of the critical temperature is observed in Al thin films, a very weakly coupled metallic superconductor, but not in more strongly coupled materials.

Description

Keywords

cond-mat.supr-con, cond-mat.supr-con, cond-mat.dis-nn

Journal Title

Physical Review B - Condensed Matter and Materials Physics

Conference Name

Journal ISSN

1098-0121
1550-235X

Volume Title

92

Publisher

American Physical Society (APS)
Sponsorship
Engineering and Physical Sciences Research Council (EP/I004637/1)
A.M.G. was supported by EPSRC, Grant No. EP/I004637/1, FCT, Grant PTDC/FIS/111348/2009, and a Marie Curie International Reintegration Grant PIRG07-GA-2010-268172. J.M. acknowledges the support of an EPSRC Ph.D. studentship.