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Colloquium:Possibilities for Novel Phases in Strongly Correlated Band Insulators

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H.R. Krishnamurthy, India Institute of Science, Bangalore
30 April 2015 from 4:00 PM to 5:00 PM
117 Osmond Laboratory
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I discuss possibilities for novel phases that can arise in simple models of strongly correlated band insulators such as the Ionic Hubbard Model with a strong onsite Coulomb repulsion energy, based on a Dynamical Mean-Field Theory treatment of the model*.  In particular, in the paramagnetic regime which can persist down to low temperatures in models with frustration, a metallic phase is induced by strong correlations! In the magnetically ordered regime, an antiferromagnetically ordered phase with different band gaps for the up and down spins ensues, including a line in parameter space where one of the spin gaps vanish, giving rise to a half-metallic antiferromagnet. Doping the band insulator in such regimes gives rise to a phase region in which the system is a half-metallic ferrimagnet. Such phases, if obtainable experimentally, would have valuable implications for spintronics.

* References:

Arti Garg, H. R. Krishnamurthy and Mohit Randeria  Can Correlations Drive a Band Insulator Metallic?  Phys. Rev. Lett. 97, 046403 (26 July 2006)

Arti Garg, H R Krishnamurthy, and Mohit Randeria   Doping a Correlated Band Insulator: A New Route to Half-Metallic Behavior    Phys. Rev. Lett. 112, 106406 (12 March 2014)

Soumen Bag, Arti Garg and H. R. Krishnamurthy  Phase Diagram of the Half-Filled Ionic Hubbard Model