Electronic Inhomogeneity in Organic Charge Transfer Salt κ-(BEDT-TTF)2Cu[N(CN)2]I Probed by Polarized Femtosecond Spectroscopy
In this study, to investigate the electronic state of organic molecular crystal κ-(BEDT-TTF)2Cu[N(CN)2]I (κ-I), polarized pump probe spectroscopy was conducted. From the observation of photoinduced carrier relaxation dynamics, we found that the carrier dynamics in κ-I are qualitatively different from those in other κ-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 TMI = 40 K, 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). Remarkably, this signal shows no clear changes at TMI = 40 K; instead, it shows an anomalous increase in the signal amplitude at T ∼ 8 K. A possible origin of this anomaly is the locally induced superconducting state.