Hierarchical excitations from correlated spin tetrahedra on the breathing pyrochlore lattice

TL;DR

This study reveals hierarchical spin excitations in the breathing pyrochlore compound CuInCr$_4$S$_8$, demonstrating an effective cluster model and highlighting the interplay of spin and lattice dynamics through neutron scattering.

Contribution

It introduces an effective cluster approach to understand spin dynamics in breathing pyrochlore lattices, supported by neutron scattering data on CuInCr$_4$S$_8$.

Findings

Hierarchical spin excitations observed via neutron scattering.

Effective model of correlated tetrahedra at low energies.

Strong magnon-phonon coupling at higher energies.

Abstract

The hierarchy of the coupling strengths in a physical system often engenders an effective model at low energies where the decoupled high-energy modes are integrated out. Here, using neutron scattering, we show that the spin excitations in the breathing pyrochlore lattice compound CuInCr$_4$S$_8$ are hierarchical and can be approximated by an effective model of correlated tetrahedra at low energies. At higher energies, intra-tetrahedron excitations together with strong magnon-phonon couplings are observed, which suggests the possible role of the lattice degree of freedom in stabilizing the spin tetrahedra. Our work illustrates the spin dynamics in CuInCr$_4$S$_8$ and demonstrates a general effective-cluster approach to understand the dynamics on the breathing-type lattices.