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Accueil du site > Séminaires > Séminaires 2010 > Phase transitions in some generalized "J-Q" type models in two dimensions

mardi 8 Juin — 14:00

Phase transitions in some generalized "J-Q" type models in two dimensions

Arnab Sen (Boston University)

par Pierre Pujol - 8 juin 2010

Senthil et al. [Science 303, 1490 (2004)] have proposed that subtle Berry phase effects in two dimensions can sometimes invalidate the well known Landau-Ginzburg-Wilson paradigm of critical phenomena and lead to a continuous phase transition between states that break different symmetries (instead of first order). The critical theory is then naturally expressed not in terms of the order parameter fields but their fractionalized versions. The S=1/2 J-Q model on the square lattice proposed by Sandvik [Phys. Rev. Lett. 98, 227202 (2007)], where spins interact with nearest-neighbor Heisenberg exchange J and a four-spin plaquette interaction Q, exhibits a transition between a Neel state (that breaks spin rotation symmetry) to a VBS state (that breaks lattice symmetries) on varying Q/J. There is strong evidence from recent numerics on large system sizes [Sandvik, Phys. Rev. Lett., 104, 177201 (2010)] that the phase transition may indeed be continuous.

We present results from a study of certain generalizations of the J-Q model on the square lattice, both in the SU(2) and U(1) case for S=1/2, with the aim to better understand the unusual critical properties of the Neel-VBS phase transition.