Nonlinear Optical Phenomena in Cyclotron Resonanceof Positive Holes and Electrons in Cu2O*

Abstract

Nonlinear optical phenomena have been observed for the first time in a new cyclotron resonance experiment on the photoexcited positive holes and/or electrons in Cu 2 O at f =35 GHz, T =4.2 K and at high density excitation P ex ≥100 kW/cm 2 of λ ex =460-750 nm. Unexpectedly, we have observed a nonlinear optical growth of the cyclotron resonance absorption of both holes and electrons at the mid-gap high-density excitation of λ ex ≥690 nm. New experimental results reveal so far unknown specific characters of the conduction and valence electrons in detail and of deep levels as well. Here, we tentatively ascribe these phenomena to a possible condensation of polarons and excitons into a new state in Cu 2 O such as into a bipolaron state via a specific type of double acceptor states.