Anisotropic propagative excitations and quadrupolar effects in Tb$_2$Ti$_2$O$_7$

TL;DR

This study investigates magnetic excitations in Tb2Ti2O7 using polarized inelastic neutron scattering, revealing anisotropic dispersive modes, anomalies in crystal field and phonons, and evidence of strong spin-lattice coupling affecting quadrupolar interactions.

Contribution

It provides new insights into the collective excitations and spin-lattice interactions in Tb2Ti2O7, highlighting the role of anisotropic propagative modes and quadrupolar effects.

Findings

Dispersive excitations emerge from pinch points with anisotropic spectral weight.

Anomalies observed in crystal field and phonon spectra at zone centers.

Strong spin-lattice coupling influences quadrupolar interactions.

Abstract

The dynamical magnetic correlations in \tbti\, have been investigated using polarized inelastic neutron scattering. Dispersive excitations are observed, emerging from pinch points in reciprocal space and characterized by an anisotropic spectral weight. Anomalies in the crystal field and phonon excitation spectrum at Brillouin zone centers are also reported. These findings suggest that Coulomb phases, although they present a disordered ground state with dipolar correlations, allow the propagation of collective excitations. They also point out a strong spin-lattice coupling, which likely drives effective interactions between the $4f$ quadrupolar moments.