Far-Infrared Spectroscopy in Spin-Peierls Compound CuGeO_3 under High Magnetic Fields

TL;DR

This study uses far-infrared spectroscopy to investigate the spin-Peierls compound CuGeO_3 under high magnetic fields, revealing phonon mode splitting and magnetic excitations related to phase transitions.

Contribution

First observation of phonon mode splitting in the incommensurate phase and identification of a magnetic excitation in CuGeO_3 using polarized FIR spectroscopy.

Findings

Splitting of folded phonon mode in IC phase

Detection of magnetic excitation at 63 cm$^{-1}$

Assignment of phonon and magnetic modes in different phases

Abstract

Polarized far-infrared (FIR) spectroscopic measurements and FIR magneto-optical studies were performed on the inorganic spin-Peierls compound CuGeO_3. An absorption line, which was found at 98 cm$^{-1}$ in the dimerized phase (D phase), was assigned to a folded phonon mode of B$_{3u}$ symmetry. The splitting of the folded mode into two components in the incommensurate phase (IC phase) has been observed for the first time. A new broad absorption centered at 63 cm$^{-1}$ was observed only in the ${\bf E}\parallel b$ axis polarization, which was assigned to a magnetic excitation from singlet ground state to a continuum state.