Quantum Phase Transition of Randomly-Diluted Heisenberg Antiferromagnet on a Square Lattice

TL;DR

This study investigates the quantum phase transition in a diluted Heisenberg antiferromagnet on a square lattice, revealing that the critical concentration aligns with percolation theory but quantum fluctuations influence the critical exponents and their dependence on spin size.

Contribution

It demonstrates that the critical concentration matches the percolation threshold and shows how quantum fluctuations cause non-universal critical exponents depending on spin size.

Findings

Critical concentration equals the 2D percolation threshold.

Quantum fluctuations alter the critical exponents from classical values.

Critical exponents depend on the spin size S.

Abstract

Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.