Evaluation of nano-space modulated structure on Tl compounds using optical second harmonic genaration

点击翻译按钮获取中文摘要

Optical second harmonic generation (SHG) has been studied in TlMeX2 (Me=In,Ga, X=S,Se,Te) compounds with layered and chain crystalline structures. For layered TlInS2 and TlGaSe2, SHG signal has been observed in a range of temperatures below the point of phase transition into ferroelectric phase for which asymmetry is prominent. On the other hand, the chain TlInSe2 and TlGaTe2 have shown SHG signal at a temperature above 270 and 293K, respectively. Both the TlInSe2 and TlGaTe2 have symmetry centre at room temperature and second order optical nonlinearity is an artefact incompatible with their bulk structure.From the results of polarization properties on TlInS2 crystals, the point group coresponding to the crystal structure of ferroelectric phase is confirmed to be C3,2.