Physics

Dr. Vikram Tripathi
TIFR, Mumbai

Abstract :  

The central feature of strongly correlated systems is strong interparticle interactions that are comparable to or more significant than their kinetic energies. Strong-correlation governs much of the new paradigms of condensed matter physics over the past few decades – it is the key ingredient in the Kondo effect, fractional quantum Hall effect, high-temperature superconductivity, heavy fermion physics, double exchange and frustrated magnetism, Wigner crystallization, and Coulomb blockade (Mott insulators).

We currently face numerous challenges in the study of strongly correlated quantum systems. First, there are technical challenges. Since interparticle interactions are rather large, conventional many-body approaches based on perturbative expansions around a non-interacting model often fail. Strong correlation by definition imposes local constraints on particle number and spin, which frequently leads to gauge theories with no small parameter. New theoretical (analytical and nu-merical) approaches are thus needed. Second, the role of disorder is poorly understood in the presence of correlations even where a good understanding exists of the disordered non-interacting counterpart.

These aspects naturally come together in the study of disordered superconductors in the vicinity of metal-insulator transitions. Superconductivity in this regime can be degraded both by the breaking of Cooper pairs as well as from an inability to establish global phase coherence. We describe a number of phenomena governed by phase fluctuation effects and the insights we have obtained.