PARAMAGNETIC-SUSCEPTIBILITY OF SEMICONDUCTING CDF2-IN CRYSTALS - DIRECT EVIDENCE OF THE NEGATIVE-U NATURE OF THE DX-LIKE CENTER

Paramagnetic susceptibility kappa(para) of CdF2 crystals with bistable In centers is measured in the temperature range T=4-300 K. For crysta ls cooled in the dark down to Liquid helium temperature, kappa(para) i s determined by the trace Mn2+ impurity. Illumination of the sample by the ultraviolet-visible light results in the appearance of the photoi nduced delta kappa(para) Signal due to formation of centers with the m agnetic moment J=1/2. This gives a clear evidence of an absence of par amagnetism in the deep state of the bistable In center and its presenc e in the shallow state, i.e., proves the negative-U nature of the deep state. (C) 1997 American Institute of Physics.