Optical absorption of CuO3 antiferromagnetic chains at finite temperatures

We use a high-statistic quantum Monte Carlo and maximum entropy regularization method to compute the dynamical energy correlation function (DECF) of the one-dimensional (1D) S = 1/2 antiferromagnetic Heisenberg model at finite temperatures. We also present a finite-temperature analytical ansatz for the DE;CT; that is in very good agreement with the numerical data in the considered temperature range. From these results, and from a finite-temperature generalization of the mechanism proposed by Lorenzana and Sawatsky [Phys. Rev. Lett. 74, 1867 (1995)]. we compute the line shape for the optical absorption spectra of multimagnon excitations assisted by phonons for quasi-1D compounds. The line shape has two contributions analogous to the Stokes and anti-Stokes process of Raman scattering. Our low-temperature data are in good agreement with optical absorption experiments of CuO3 chains in Sr2CuO3. Out finite-temperature results provide a nontrivial prediction on the dynamics of the Heisenberg model at finite temperatures that is easy to verify experimentally.