Anomalous frequency and intensity scaling of collective and local modes in a coupled spin tetrahedron system

TL;DR

This study investigates the magnetic excitation spectrum of a coupled spin tetrahedral system, revealing anomalous scaling behaviors of collective and local modes through Raman scattering, highlighting complex magnetic interactions and fluctuations.

Contribution

It provides new insights into the temperature-dependent behavior of magnetic excitations in a coupled spin tetrahedron system, emphasizing the role of singlet fluctuations and mode localization.

Findings

Two modes shift significantly with temperature, resembling order parameters.

Two modes show negligible temperature dependence and dissolve above T_N.

Observation of a broad continuum indicating complex spin dynamics.

Abstract

We report on the magnetic excitation spectrum of the coupled spin tetrahedral system Cu$_{2}$Te$_{2}$O$_{5}$Cl$_{2}$ using Raman scattering on single crystals. The transition to an ordered state at T$_{N}^{Cl}$=18.2 K evidenced from thermodynamic data leads to the evolution of distinct low-energy magnetic excitations superimposed by a broad maximum. These modes are ascribed to magnons with different degree of localization and a two-magnon continuum. Two of the modes develop a substantial energy shift with decreasing temperature similar to the order parameter of other Neel ordered systems. The other two modes show only a negligible temperature dependence and dissolve above the ordering temperature in a continuum of excitations at finite energies. These observations point to a delicate interplay of magnetic inter- and intra-tetrahedra degrees of freedom and an importance of singlet fluctuations in describing a spin dynamics.