Quantum Isotope Effect in Silicon at Low Temperatures

High-precision studies of Raman scattering in isotopically pure Si-28, Si-29, Si-30 single crystals have been performed in the temperature range from 8 to 300 K. It has been found that a difference of about (0.4 +/- 0.1) cm(-1) observed at temperatures T 100 K between the normalized Raman frequencies of the Si-28 and Si-30 isotopes measured with an accuracy of 0.1 cm(-1) is certainly due to quantum effects damping with increasing temperature. The possibility of observing quantum isotope effects in germanium has been estimated using experimental data on isotope effects in diamond and silicon.