Multiple Magnon Modes and Consequences for the Bose-Einstein Condensed Phase in BaCuSi2O6

TL;DR

This study reveals multiple magnon modes in BaCuSi2O6, showing complex spin dynamics and a unique Bose-Einstein condensate phase with spatial modulation, advancing understanding of quantum magnetism.

Contribution

It provides the first detailed inelastic neutron scattering analysis of multiple magnon modes and their impact on the BEC phase in BaCuSi2O6.

Findings

Multiple magnon modes observed, indicating inequivalent dimer sites

Complex spin Hamiltonian leads to a spatially modulated BEC phase

Higher energy resolution clarifies spin dynamics

Abstract

The compound BaCuSi2O6 is a quantum magnet with antiferromagnetic dimers of S = 1/2 moments on a quasi-2D square lattice. We have investigated its spin dynamics by inelastic neutron scattering experiments on single crystals with an energy resolution considerably higher than in an earlier study. We observe multiple magnon modes, indicating clearly the presence of magnetically inequivalent dimer sites. This more complex spin Hamiltonian leads to a distinct form of magnon Bose-Einstein condensate (BEC) phase with a spatially modulated condensate amplitude.