Broken translational and rotational symmetries in LiMn1.5Ni0.5O4 spinel

TL;DR

This study reveals how long-range magnetic ordering in LiMn1.5Ni0.5O4 induces broken rotational and translational symmetries, affecting lattice vibrations and indicating coupled charge and magnetic transitions.

Contribution

It demonstrates the signatures of broken symmetries in LiMn1.5Ni0.5O4 through Raman scattering, linking magnetic order, charge ordering, and phonon behavior.

Findings

Sharp phonon frequency shifts near magnetic transition temperature

Anomalous phonon evolution indicating broken translational symmetry

Strong coupling between lattice vibrations and magnetic degrees of freedom

Abstract

In condensed matter physics broken symmetries and emergence of quasi-particles are intimately linked to each other. Whenever a symmetry is broken, it leaves its fingerprints, and that may be observed indirectly via its influence on the other quasi-particles. Here, we report the strong signature of broken rotational symmetry induced due to long range-ordering of spins in Mn - sublattice of LiMn1.5Ni0.5O4 below Tc ~ 113 K reflected with the marked changes in the lattice vibrations using Raman scattering. In particular, the majority of the observed first-order phonon modes show a sharp shift in frequency in the vicinity of long range magnetic-ordering temperature. Phonons exist in a crystalline system because of broken translational symmetry, therefore any renormalization in the phonon-spectrum could be a good gauge for broken translational symmetry. Anomalous evolution of the few modes associated with stretching of Mn/NiO6 octahedra in the intermediate temperature range (~ 60-260 K) marked the broken translational symmetry attributed to the charge ordering. Interestingly same modes also show strong coupling with magnetic degrees of freedom, suggesting that charge-ordering and magnetic transition may be linked to each other.