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Seminars and Colloquia


Prospects of Anderson's theorem for strongly correlated disordered superconductors 
Wed, Apr 04, 2018,   04:00 PM at Physics Seminar Room 31, 2nd Floor, Main Building

Dr. Amit Ghoshal
IISER Kolkata

Abstract : 
When mutually repelling electrons wander through rugged land of impurities, fascinating properties emerge. While the complex teamwork of interactions and disorder has eluded physicists, it offers a simple and intuitive grasp of the intricate physics of disordered high temperature superconductors. Impurities impede conduction of electrons and thereby cause electrical resistance in materials. In a stark contrast, resistance-less transport in a metallic BCS superconductor is not affected by the presence of impurities! This inexplicable truism is Anderson's theorem. It arises from superconducting glue pairing up an 'up'- and a 'down'-spin electrons even when their wavefunctions include disorder -- as long as they are not strongly localized in space. The newer superconductors, whose survival is fast approaching the ambient temperatures of some parts of world, are believed to be extremely sensitive to dirts. But times are changing! Anderson's theorem is lurking in these 'high temperature' superconductors according to several recent studies. In this talk, we establish that the 'normal states', the electronic wavefunctions before the pairing glue is turned on, underpin non-trivial footprints of the delicate balance of strong electronic repulsions and disorder. In the process of forming 'Cooper-pairs' these 'dressed' electrons do not feel dirts at all. This is similar to the fact that Bloch electrons do not scatter off the lattice potential, as the lattice is a part of Bloch wavefunctions already! The anisotropic order parameter, the hallmark of high temperature superconductors, survives as long as `normal states' have some spatial overlaps among themselves. Our results explain some of the striking findings of recent experiments on high temperature cuprate superconductors.

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