Eur. Phys. J. B 54, 465-469 (2006)
https://doi.org/10.1140/epjb/e2007-00030-x

The oxygen isotope effect on the infrared photo-induced absorption spectra of La₂CuO₄

¹ Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
² Laboratory for Neutron Scattering, ETH Zürich and PSI, 5232 Villigen PSI, Switzerland
³ University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
⁴ Physik-Institut der Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland

Corresponding author: ^a Roman.Yusupov@ijs.si

Received: 8 November 2006
Revised: 11 December 2006
Published online: 3 February 2007

Abstract

The infrared photo-induced spectra of the isotope-substituted stoichiometric La₂CuO₄ samples were studied at T=20 K. Measured spectra were analyzed within the small polaron hopping theory. A small, but detectable shift of the effective phonon frequency on the substitution ¹⁶O to ¹⁸O is found for the high-energy surface carrier associated band (~4000 cm^-1) and has a value of α_O = 0.3 ±0.2. The low-energy band (~1500 cm^-1) originating from the bulk carriers doesn't show any difference within experimental error which is fully in agreement with theory predictions. The isotope shifts of the optically active oxygen-related phonon modes are described well by the harmonic approximation.