Collective orbital excitations in orbitally ordered YVO3 and HoVO3

TL;DR

This paper investigates the nature of a 0.4 eV orbital absorption band in YVO3 and HoVO3, attributing it to two-orbiton excitations rather than local crystal-field effects, supported by experimental and theoretical analysis.

Contribution

The study introduces a microscopic model identifying the 0.4 eV absorption band as a two-orbiton excitation, challenging previous local crystal-field interpretations.

Findings

The 0.4 eV band appears only in the monoclinic phase.

The band is attributed to two-orbiton exchange processes.

Spectral weight matches theoretical predictions.

Abstract

We study orbital excitations in the optical absorption spectra of YVO3 and HoVO3. We focus on an orbital absorption band observed at 0.4 eV for polarization E parallel c. This feature is only observed in the intermediate, monoclinic phase. By comparison with the local crystal-field excitations in VOCl and with recent theoretical predictions for the crystal-field levels we show that this absorption band cannot be interpreted in terms of a local crystal-field excitation. We discuss a microscopic model which attributes this absorption band to the exchange of two orbitals on adjacent sites, i.e., to the direct excitation of two orbitons. This model is strongly supported by the observed dependence on polarization and temperature. Moreover, the calculated spectral weight is in good agreement with the experimental result.