Hierarchical excitations from correlated spin tetrahedra on the breathing pyrochlore lattice

29 Jan 2021  ·  Shang Gao, Andrew F. May, Mao-Hua Du, Joseph A. M. Paddison, Hasitha Suriya Arachchige, Ganesh Pokharel, Clarina dela Cruz, Qiang Zhang, Georg Ehlers, David S. Parker, David G. Mandrus, Matthew B. Stone, Andrew D. Christianson ·

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.

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Strongly Correlated Electrons