Third-order optical nonlinearities of lead halide perovskite single crystals*

Lead halide perovskite semiconductors, MAPbX₃ (MA = CH₃NH₃, X = I, Br, and Cl), have attracted much attention as a new class of photonic device materials because of their excellent optoelectronic properties. Recently, we found unique nonlinear optical responses such as large optical modulation [1] and efficient higher-order harmonic generation [2] in MAPbX₃ perovskites. However, the origin of large nonlinear optical responses remains unclear.
In this work, we determined the third-order nonlinear optical coefficients of the wide-gap semiconductor MAPbCl₃ single crystals by using the Z-scan method. We measured the excitation wavelength and polarization dependences of these coefficients. It is found that the absolute values of coefficients depended on the crystal orientation of perovskite single crystals. These excitation wavelength dependences can be quantitatively explained by a two-band model including the exciton effect and Kane’s kp theory. The Kane energy and the exciton reduced mass of MAPbCl₃ were determined [3].
[1] T. Handa et al., Sci. Adv. 5, eaax0786 (2019).
[2] H. Hirori et al., APL Mater. 7, 041107 (2019).
[3] K. Ohara et al., Phys. Rev. Mater. 3 (2019) in press.