LaBella et al. (Reports, 25 May 2001, p. 1518) reported that "a large spin-polarized (~92%) current can be injected into GaAs [gallium arsenide] at high temperatures (100 K)," using a "100% spin-polarized" scanning tunneling microscope (STM) tip as the electron source. Egelhoff et al. comment that, in relating the measured polarization in the light emitted from the GaAs to the spin polarization of the injected electrons, LaBella et al. neglected to corrrect for refraction as the light left the sample; suggest that the group did not measure the spin-relaxation lifetime value of the sample used, which bears on the relationship between the electron spin polarization at recombination and the injected-current polarization; and argue that it is unlikely that the electrons emitted from the STM were indeed 100% spin polarized. Thus, Egelhoff et al. conclude, "an electron spin polarization at recombination of 25.2% can be inferred from these experiments," not the 92% cited in the original report. LaBella et al., in their response, agree that their analysis did not adequately account for refraction and acknowledge that they did not measure the spin-relaxation lifetime for the sample studied, although they used a published value for GaAs of a similar hole density and temperature.The full text of these comments can be seen at www.sciencemag.org/cgi/content/full/296/5571/1195a
