Inhomogeneous ferroelectric polarization in α'-(BEDT-TTF)_2IBr_2 revealed by second-harmonic generation microscopy

摘要

This paper reports the observation of optical second-harmonic generation (SHG) in an organic conductor α'-(BEDT-TTF)_2IBr_2. The charge-transfer complex undergoes a semiconductor-to-semiconductor transition around 200K due to charge ordering. Activation of SHG manifested that the complex generates ferroelectric polarization in the charge ordered phase. The observation of the image of SHG revealed that the nonlinear optical signal was generated from limited regions of the single crystal. The inhomogeneous distribution of SHG signal is discussed in terms of the possible competition of ferroelectric and non-polar phases in the phase diagram of the compound.