Spin excitations in the two-dimensional strongly coupled dimer system malachite

TL;DR

This study investigates the spin excitation spectrum of malachite, revealing a two-dimensional dimerized magnetic system with strong interdimer interactions, which may exhibit unconventional quantum criticality.

Contribution

It identifies a new two-dimensional dimerized coupling scheme in malachite with strong interdimer interactions, bridging different magnetic models and suggesting potential for unconventional quantum critical behavior.

Findings

Malachite exhibits dispersive gapped singlet-triplet excitations.

The coupling scheme has a strong interdimer interaction with J'/J1~0.3.

The interaction geometry resembles the staggered dimer lattice.

Abstract

The mineral malachite, Cu2(OD)2CO3, has a quantum spin-liquid ground state and no long-range magnetic order down to at least T=0.4 K. Inelastic neutron scattering measurements show that the excitation spectrum consists of dispersive gapped singlet-triplet excitations, characteristic of spin-1/2 dimer-forming Heisenberg antiferromagnets. We identify a new two-dimensional dimerized coupling scheme with strong interdimer coupling J'/J1~0.3 that places malachite between strongly coupled alternating chains, square lattice antiferromagnets, and infinite-legged ladders. The geometry of the interaction scheme resembles the staggered dimer lattice, which may allow unconventional quantum criticality.