Negative Photoconductance in a Single Crystal of C₆₀

Abstract

In a single crystal of C₆₀, a decrease in conductance (negative photoconductance) with a response time of --0.01 s, followed by positive photoconductance with a longer response time, was observed upon irradiation with chopped light in a narrow energy region centered at 1.65 eV at room temperature. With decreasing temperature, the positive photoconductance is suppressed, but the negative photoconductance increases and has an increased response time. The dramatic relationship between the positive and negative photoconductances appears in a limited temperature range near that of the structural phase transition. The result can be interpreted by assuming the coexistence of traps with a slow thermal ejection rate and rapid recombination centers after Stöckmann.