Schedule Jun 08, 2004
Landau Forbidden Transitions and Deconfined Criticality in Quantum Magnets
Ashvin Vishwanath (UC ~ Berkeley)

Our modern understanding of phase transitions is built on Landau's theory, which, among other things, dictates when it may be possible to have a continuous transition between two phases. For example, a continuous transition between two phases with unrelated orders is forbidden in this theory without special fine tuning. In this talk I will argue that in the case of quantum phase transition, precisely such `Landau forbidden' phase transition may occur. In particular, a theory for a direct continuous transition between the Neel and VBS phases of a two dimensional quantum magnet will be presented. This critical theory is naturally described in terms of fractionalized excitations (spinons) and a conserved flux that only emerges at the transition. The critical theory will be developed by starting from the Neel ordered phase and understanding precisely the role played by hedgehog defects in the Neel field. The possible relevance of this physics to phenomena in strongly correlated materials will be briefly discussed.

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