Spin dynamics of coupled spin ladders near quantum criticality in Ba2CuTeO6

TL;DR

This study investigates the magnetic excitations in Ba2CuTeO6 using neutron scattering, revealing its proximity to a quantum critical point between gapped and ordered magnetic phases, and provides detailed exchange parameters.

Contribution

It offers the first detailed characterization of spin dynamics in Ba2CuTeO6, establishing its position near quantum criticality and determining exchange interactions through combined experimental and theoretical analysis.

Findings

Ba2CuTeO6 is close to the quantum critical point between gapped and magnetic order phases.

Exchange parameters for intra- and interladder couplings are quantitatively determined.

High field magnetization data agree with quantum Monte Carlo predictions.

Abstract

We report inelastic neutron scattering measurements of the magnetic excitations in Ba2CuTeO6, proposed by ab initio calculations to magnetically realize weakly coupled antiferromagnetic two-leg spin-1/2 ladders. Isolated ladders are expected to have a singlet ground state protected by a spin gap. Ba2CuTeO6 orders magnetically, but with a small Neel temperature relative to the exchange strength, suggesting that the interladder couplings are relatively small and only just able to stabilize magnetic order, placing Ba2CuTeO6 close in parameter space to the critical point separating the gapped phase and Neel order. Through comparison of the observed spin dynamics with linear spin wave theory and quantum Monte Carlo calculations, we propose values for all relevant intra- and interladder exchange parameters, which place the system on the ordered side of the phase diagram in proximity to the critical point. We also compare high field magnetization data with quantum Monte Carlo predictions for the proposed model of coupled ladders.