Photocurrent suppression near antiferromagnetic transition in an organic Mott‐insulator β′‐(BEDT‐TTF)(TCNQ) crystal

We measured the temperature dependence of the photocurrent in an organic Mott-insulator beta'-(bis(ethylenedithio)-tetrathiafulvalene)(7,7,8,8-tetracyanoquinodimethane) (BEDT-TTF)-(TCNQ) crystal with applied bias voltage along the c- and b-axis up to 12 V. A semiconductor laser with a wavelength of 405nm was used as the light source. We observed that with increasing bias voltage, the temperature at which the photocurrent starts to flow decreases down to 16 K, near the antiferromagnetic (AF) transition temperature of BEDT-TTF (T-N = 20K). This result indicates that the AF transition plays an important role in the suppression of photogenerated carrier conduction. The creation of strongly bound holon doublon clusters, which are expected to exist in the AF spin order states, is identified as one of the factors responsible for the photocurrent suppression. Above the T-N, it was confirmed that both the photogenerated electron and hole can be comparably detected as the photocurrent by changing the polarity of the bias voltage. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim