New Far Infrared Vibrational Mode in Zn Doped CuGeO3

TL;DR

This study investigates the effects of Zn doping on the far infrared vibrational modes in CuGeO3, revealing new absorption lines linked to localized lattice modes and their temperature and doping dependence.

Contribution

It identifies and characterizes new far infrared absorption lines in Zn-doped CuGeO3, suggesting their origin as localized lattice modes associated with zinc ions.

Findings

Zn doping introduces new absorption lines between 5 and 55 cm-1.

Absorption intensity saturates above 2% Zn doping.

The lines are temperature and magnetic field independent, absent in Si-doped samples.

Abstract

We report on far infrared measurements on Zn and Si doped crystals of the spin-Peierls compound CuGeO3. Zn doping has the effect of introducing several new absorption lines, polarized in the ab-plane, between 5 and 55 cm-1. The intensity of the absorption grows with Zn concentration but saturates above 2% Zn. One line at 10 cm-1 loses intensity above 4K, and a second line at 20 cm-1 is absent at low temperatures but grows to peak at about 40K in agreement with a three level model with two excited states 10 and 30 cm-1 above the ground state. As the doping is increased these lines broaden, and a temperature independent absorption developes over the entire range from 5 to 55 cm-1. These features are magnetic field independent up to 16T and are absent in Si doped samples. We suggest the new absorption is due to localized lattice modes of the zinc ion and the surrounding GeO4 tetrahedra.