Electronic Inhomogeneity In Organic Charge Transfer Salt Kappa-(Bedt-Ttf)(2)Cu[N(Cn)(2)]I Probed By Polarized Femtosecond Spectroscopy

In this study, to investigate the electronic state of organic molecular crystal kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]I (kappa-1), polarized pump probe spectroscopy was conducted. From the observation of photoinduced carrier relaxation dynamics, we found that the carrier dynamics in kappa-I are qualitatively different from those in other kappa-type salts and inhomogeneous electronic states are realized in the single crystal. As temperature decreases, the transient polarization anisotropy along the c axis associated with a charge order develops below T-MI = 40K, which is consistent with the metal insulator transition observed in the resistivity measurement. Moreover, we found the position where the transient polarization anisotropy is enhanced along the 1/2 (a + c) direction. Remarkably, this signal shows no clear changes at T-MI = 40 K; instead, it shows an anomalous increase in the signal amplitude at T similar to 8 K. A possible origin of this anomaly is the locally induced superconducting state.