## Abstract

The quantum phase transition between a spin gap state and an antiferromagnetic phase is investigated. We study S=1/2 antiferromagnetic Heisenberg chains coupled by antiferromagnetic interchain interaction. The intrachain exchanges have alternating strength. The phase boundary between the antiferromagnetically ordered phase and a spin gap phase is also obtained in a parameter space of the amplitude of the interchain coupling and the dimerization. The spin-wave approximation substantially overestimates the antiferromagnetic phase. The competition between the long range order and the spin gap is examined in detail. We estimate a variety of critical exponents at the transition, namely, exponents v, θ and z defined as the exponent of the correlation length, the magnetization curve and the dynamical exponent, respectively. From the quantum Monte Carlo simulation, the exponents v, θ and z are estimated to be unity. The exponents v and θ are different from the estimated values in one dimension. It suggests that the universality changes due to the dimensionality change. In our estimates, the exponent v does not agree with the prediction from three dimensional classical Heisenberg model. We also discuss the relevance of our result to spin-Peierls systems with lattice distortion.

Original language | English |
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Pages (from-to) | 4529-4541 |

Number of pages | 13 |

Journal | journal of the physical society of japan |

Volume | 63 |

Issue number | 12 |

DOIs | |

Publication status | Published - 1994 |

Externally published | Yes |

## Keywords

- antiferromagnetic long range order
- critical exponents
- dimerization
- interchain coupling
- quantum Monte Carlo simulation
- spin gap

## ASJC Scopus subject areas

- Physics and Astronomy(all)