Physical Review Letters
Magnetic Raman Scattering from 1D Antiferromagnets
Rajiv R. P. Singh, Peter Prelovšek, B. Sriram Shastry
Abstract
We study Raman scattering from 1D antiferromagnets within the Fleury-Loudon scheme by applying a finite temperature Lanczos method to a 1D spin-half Heisenberg model with nearest-neighbor ( ${J}_{1}$) and second-neighbor ( ${J}_{2}$) interactions. The low-temperature spectra are analyzed in terms of the known elementary excitations of the system for ${J}_{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ and ${J}_{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$. We find that the low- $T$ Raman spectra are very broad for $|{J}_{2}/{J}_{1}|\ensuremath{\le}0.3$. This broad peak gradually diminishes and shifts with temperature, so that at $T>{J}_{1}$ the spectra are narrower and peaked at low frequencies. The experimental spectra for ${\mathrm{CuGeO}}_{3}$ are discussed in light of our calculations.