We propose an interpretation for the hump observed in the optical conductivity at or below a few hundreds of cm−1, in overdoped cuprates like the electron-doped Nd_{2-x}Ce_xCuO_{4-y} at x\gtrsim 0.15 and the hole-doped Bi_2Sr_2CuO_6 and La_{2-x}Sr_xCuO_4. This interpretation is based on the direct excitation of charge collective modes, which become nearly critical in the proximity to a charge-ordering instability. The nearly critical character of these excitations entails a peculiar temperature dependence and a pseudo-scaling form of the lineshapes, which are in agreement with the experimental data.
@article{arxiv.cond-mat/0108039,
title = {Anomalous optical absorption in overdoped cuprates near the charge-ordering instability},
author = {S. Caprara and C. Di Castro and S. Fratini and M. Grilli},
journal= {arXiv preprint arXiv:cond-mat/0108039},
year = {2009}
}