Lattice dynamics and spin-phonon coupling in the kagome spin ice HoAgGe

TL;DR

This study uses Raman spectroscopy and first-principles calculations to explore lattice dynamics and spin-phonon interactions in HoAgGe, revealing finite coupling effects across magnetic phase transitions in this kagome spin ice compound.

Contribution

It provides the first detailed investigation of spin-phonon coupling in HoAgGe using combined experimental and theoretical approaches.

Findings

Detection of eight Raman-active phonon modes consistent with calculations

Observation of phonon mode hardening and softening across magnetic transitions

Identification of electron-phonon coupling via Fano lineshape in a high-energy mode

Abstract

We employ polarization-resolved Raman spectroscopy and first-principles phonon calculations to study the lattice dynamics and spin-phonon coupling in the kagome spin ice compound HoAgGe. Upon cooling, HoAgGe shows transitions from a nonmagnetic state at 300 K to a partially magnetic-ordered phase below T2 = 11.6 K, eventually reaching a fully-magnetic ordered phase below T1 = 7 K. We detect eight of ten Raman-active phonon modes at room temperature, with frequencies consistent with first-principles phonon calculations. We find that the low-energy phonon modes harden upon cooling, soften slightly below T2, and finally harden again below T1, suggesting finite spin-phonon coupling in HoAgGe. Furthermore, one high-energy mode at 185 cm-1 with E' symmetry exhibits a Fano lineshape due to electron-phonon coupling. Our Raman results establish finite spin-phonon coupling and electron-phonon coupling in the magnetic phase of HoAgGe, providing a foundation for future studies of the novel field-induced phases at low temperatures in HoAgGe.