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Metal-insulator transitions (MIT), driven entirely by strong electron-electron interactions and/or disorder, continue to underpin many novel phenomena in quantum matter. We study disorder-driven MITs in the "strong disorder" category using a novel semi-analytic cluster adaptation of dynamical mean-field theory (CDMFT) for the simplest, binary-alloy disorder (also known as spinless Falicov-Kimball, or "simplified" Hubbard) model. Such an (oversimplified) model is a caricature for a disordered system where mobile electrons interact strongly with positionally random, localized charges. We uncover anomalous quantum criticality in the full dc conductivity tensor across the MIT which, remarkably, is reminiscent of "Mott quantum criticality" that obtains at the low-T end-point of the line of first-order transitions in the Hubbard model (experimentally best studied for 2D organics). Interestingly, such novel criticality is also found to underpin thermal transport (heat conductivity, Seebeck co-efficient, Lorenz number) across the MIT. Moreover, we also provide an explicit realization of the famed "universal dielectric response" (UDR) of Jonscher in optical responses across the MIT. The associated stretched-exponential relaxation in the long-time dielectric response strongly suggests anomalous diffusion, an emergent "electron glassy" dynamics and weak ergodicity breaking. These findings suggest that a truly novel type of carrier localization obtains in the "strong disorder" limit.

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Mukul Laad, IMSc, Chennai
Seminar Room 0.02, ETP
Contact: Simon Trebst