UC San Diego

We report on the electromagnetic response of digital ferromagnetic heterostructures (DFH): systems with δ-doped MnAs layers separated by GaAs spacers of variable thickness (y). The gross features of the infrared conductivity of DFH samples are consistent with the notion that these digital structures are GaAs/Ga1-xMnxAs superlattices. This conclusion is supported by a combination of spectral weight analysis and effective medium theory. The optical properties of DFH also provide insights into the evolution of their critical temperature with GaAs spacing. In DFH a low-lying gap materializes in the energy dependent conductivity, which is interpreted as a mobility gap resulting from Anderson localization.