Infrared absorption measurements in the range of 125 to 700 cm^(-1) have been carried out as a function of temperature upto 5 K in MgB2. The absorption spectrum is characterised by a broad band centred at 485 cm^{-1}, with shoulders at 333 and 387 cm^{-1}. Studies on the temperature dependence of absorption, indicate that these modes initially harden with the lowering of temperature, and this trend is arrested at ~ 100 K, below which they soften. Further, in the case of the mode at 333 cm^{-1}, there is a distinct softening associated with the superconducting transition at 39 K. The implications of these experimental results in the context of superconductivity in MgB2 are discussed.
@article{arxiv.cond-mat/0104354,
title = {Infrared absorption in superconducting MgB2},
author = {C. S. Sundar and A. Bharathi and M. Premila and T. N. sairam and S. Kalavathi and G. L. N. Reddy and V. S. Sastry and Y. Hariharan and T. S. Radhakrishnan},
journal= {arXiv preprint arXiv:cond-mat/0104354},
year = {2007}
}