Finite-Temperature Transition in the Spin-Dimer Antiferromagnet BaCuSi2O6

TL;DR

This paper investigates the finite-temperature phase transition in a frustrated spin-dimer antiferromagnet, revealing a crossover from 3D XY universality to a different critical behavior due to fluctuation-induced interactions.

Contribution

It introduces a new scenario for the critical behavior in frustrated antiferromagnets, showing instability of the 3D XY fixed point caused by fluctuation-induced biquadratic interactions.

Findings

Monte Carlo simulations support the existence of a transient 3D XY critical region.

Scaling arguments show the decoupled fixed point is unstable against biquadratic interactions.

A crossover to nontrivial critical phenomena with different exponents occurs near the critical point.

Abstract

We consider a classical XY-like Hamiltonian on a body-centered tetragonal lattice, focusing on the role of interlayer frustration. A three-dimensional (3D) ordered phase is realized via thermal fluctuations, breaking the mirror-image reflection symmetry in addition to the XY symmetry. A heuristic field-theoretical model of the transition has a decoupled fixed point in the 3D XY universality, and our Monte Carlo simulation suggests that there is such a temperature region where long-wavelength fluctuations can be described by this fixed point. However, it is shown using scaling arguments that the decoupled fixed point is unstable against a fluctuation-induced biquadratic interaction, indicating that a crossover to nontrivial critical phenomena with different exponents appears as one approaches the critical point beyond the transient temperature region. This new scenario clearly contradicts the previous notion of the 3D XY universality.