Time-Resolved Measurement of the Photoinduced Change in the Electrical Conductivity of the Organic Superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br

摘要

Photoinduced change in the electrical conductivity of a single crystal of k-(BEDT-TTF)2Cu[N(CN)2]Br (k-Br) has been examined at various temperatures in the vicinity of the metal-superconductor phase-transition temperature (T_c) with a nanosecond visible laser pulse. The transient change of the electric potential difference was measured following photoirradiation, and the time profile of the electrical conductivity was obtained in the current-biased sample. Upon photoirradiation, the bulk resistance increases at all the temperatures under the present study. However, the decay profile shows a marked temperature dependence, and a prolongation of the decay time is observed at temperatures just below T_c. The relaxation times below and above T_c are different from each other, and unconventional asymmetry of the critical slowing down about T_c is found. The presence of a nonthermal (nonbolometric) photoirradiation effect is confirmed in the superconducting phase of k-Br based on the analysis of the temperature dependence of the photoresponse in the conductivity.