Optically Induced Gap in the Atomic Tunneling Spectrum ofAs2S3Glass

Irradiation of the amorphous semiconductor ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ with band-edge photons opens a metastable gap in the low-energy density of states of atomic tunneling systems. Electric resonance studies at temperatures below 1 K indicate the annihilation of ∼ ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ tunneling centers, close to the density of metastable paramagnetic electronic defects created by low-level optical excitation. These findings link low-energy atomic tunneling systems to localized midgap electronic states.