Probing scattering of Raman phonons on magnetic and electronic excitations in pyrochlores Nd$_2$Zr$_2$O$_7$ and Nd$_2$Ir$_2$O$_7$

TL;DR

This study uses Raman scattering spectroscopy to investigate phonon and crystal field excitations in Nd-based pyrochlores, revealing interactions between phonons, crystal fields, and electrons in different electronic states.

Contribution

It provides a comparative analysis of Raman scattering in Nd$_2$Zr$_2$O$_7$ and Nd$_2$Ir$_2$O$_7$, highlighting interactions between lattice vibrations, crystal field excitations, and electronic degrees of freedom.

Findings

Distinguished phonon interactions in insulating and semimetallic pyrochlores.

Identified scattering processes involving phonons, crystal field excitations, and electrons.

Highlighted differences in excitation interactions between Nd$_2$Zr$_2$O$_7$ and Nd$_2$Ir$_2$O$_7$.

Abstract

Magnetic rare earth atoms on pyrochlore lattice can produce such exotic magnetic states as spin ice and quantum spin ice. These states are a result of the frustration in the pyrochlore lattice, as well as crystal field degrees of freedom of rare earth atoms, and their interactions with the lattice. Raman scattering spectroscopy, which possess high spectral resolution and can easily access broad energy and temperature ranges, is an optimum tool to study these excitations and their interactions. In this work we follow Raman scattering of zone center phonons and crystal field excitations of Nd$^{3+}$ in Nd$_2$Zr$_2$O$_7$ and Nd$_2$Ir$_2$O$_7$ in the temperature range where these materials are paramagnetic. A comparison between an insulating Nd$_2$Zr$_2$O$_7$ and semimetallic Nd$_2$Ir$_2$O$_7$ materials allow us to distinguish between scattering of phonons on other phonons, crystal field excitations, and electrons, highlighting interactions between these degrees of freedom.