Quantum Monte Carlo approach to the quantum phase transition in low-dimensional antiferromagnets in terms of the Berry phase

Anders W. Sandvik, Elbio R. Dagotto, Douglas J. Scalapino

Munehisa Matsumoto, Hajime Takayama

Matthias Troyer, Masatoshi Imada, Kazuo Ueda

We have performed a large scale quantum Monte Carlo study of the quantum phase transition in a planar spin-1/2 Heisenberg antiferromagnet with CaV4O9 structure. We obtain a dynamical exponent z=1.018+/-0.02. The critical exponents beta, nu and eta agree within our errors with the classical 3D O(3) exponents, expected from a mapping to the nonlinear sigma model. This confirms the conjecture of Chubukov, Sachdev and Ye [Phys. Rev. B 49, 11919 (1994)] that the Berry phase terms in the planar Heisenberg antiferromagnet are dangerously irrelevant.

Anders W. Sandvik, Marco Vekić

Steinar Kragset, E. Smørgrav, J. Hove +2 more

Quantum phase transitions in Mott insulators do not fit easily into the Landau-Ginzburg-Wilson paradigm. A recently proposed alternative to it is the so-called deconfined quantum criticality scenario, providing a new paradigm for quantum phase transitions. In this context it has recently been proposed that a second-order phase transition would occur in a two-dimensional spin 1/2 quantum antiferromagnet in the deep easy-plane limit. A check of this conjecture is important for understanding the phase structure of Mott insulators. To this end we have performed large-scale Monte Carlo simulations on an effective gauge theory for this system, including a Berry-phase term that projects out the S=1/2 sector. The result is a first-order phase transition, thus contradicting the conjecture.

Steinar Kragset, E. Smørgrav, J. Hove +2 more

Quantum phase transitions in Mott insulators do not fit easily into the Landau-Ginzburg-Wilson paradigm.A recently proposed alternative to it is the so-called deconfined quantum criticality scenario, providing a new paradigm for quantum phase transitions.In this context it has recently been proposed that a second-order phase transition would occur in a two-dimensional spin 1=2 quantum antiferromagnet in the deep easy-plane limit.A check of this conjecture is important for understanding the phase structure of Mott insulators.To this end we have performed large-scale Monte Carlo simulations on an effective gauge theory for this system, including a Berry-phase term that projects out the S 1=2 sector.The result is a first-order phase transition, thus contradicting the conjecture.