Two-particle decay and quantum criticality in dimerized antiferromagnets

TL;DR

This paper investigates how two-particle decay processes influence quantum criticality in dimerized antiferromagnets, revealing a cubic term in the critical theory and explaining deviations from standard universality through analytical and numerical methods.

Contribution

It identifies a non-trivial cubic term in the order-parameter field theory and analyzes its impact on critical behavior and scaling corrections in dimerized antiferromagnets.

Findings

Critical exponents match O(3) universality class

Large corrections to scaling observed

Two-particle decay influences leading corrections

Abstract

In certain Mott-insulating dimerized antiferromagnets, triplet excitations of the paramagnetic phase can decay into the two-particle continuum. When such a magnet undergoes a quantum phase transition into a magnetically ordered state, this coupling becomes part of the critical theory provided that the lattice ordering wavevector is zero. One microscopic example is the staggered-dimer antiferromagnet on the square lattice, for which deviations from O(3) universality have been reported in numerical studies. Using both symmetry arguments and microscopic calculations, we show that a non-trivial cubic term arises in the relevant order-parameter quantum field theory, and assess its consequences using a combination of analytical and numerical methods. We also present finite-temperature quantum Monte Carlo data for the staggered-dimer antiferromagnet which complement recently published results. The data can be consistently interpreted in terms of critical exponents identical to that of the standard O(3) universality class, but with anomalously large corrections to scaling. We argue that the two-particle decay of critical triplons, although irrelevant in two spatial dimensions, is responsible for the leading corrections to scaling due to its small scaling dimension.