Measurement of c-axis optical absorptivity of La1.87Sr0.13CuO4

We have directly measured the c-axis optical absorptivity of a large single crystal of La1.87Sr0.13CuO4 between 9 and 80 cm-1 at 2 K using Fourier transform spectroscopy and an absorbed power technique. We seen an absorptivity onset at 41 cm-1, which is 2 - 3 cm-1 higher than that measured at 6 K with reflectance on the same sample, suggesting that a significant fraction of the electrons remain unpaired at 6 K. The absorption increases with frequency below the onset, increasing from 0.3% at 9 cm-1 to 8% at 40 cm-1. Our data are particularly significant at frequencies below the plasma edge, for which the reflectance is close to unity.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.