Investigation of anisotropic π plasmon induced by the intrinsic crystallographic defects in topological crystalline insulator material-tin-substitutional lead selenide (Pb_1-xSn_xSe)

The presence of intrinsic defects in topological crystalline insulator materials has been predicted to improve the thermoelectric figure-of-merit values in the literature. Performing atomic-resolved high angle annular dark field imaging, momentum-resolved electron energy loss spectroscopy, and electron spectroscopic diffraction, we observed those intrinsic defects, including interstitial Se atoms and Se vacancies, to cause localized mirror symmetry breaking and further result in the anisotropic π-plasmon dispersion along the Γ X ¯ and Γ M ¯ directions in single-crystal Pb1-xSnxSe (x = 0 and 0.34). In addition to the anisotropic π plasmon dispersion, the splitting lines along the Γ X ¯ direction were revealed with selected π plasmon energy in the electron spectroscopic diffraction pattern.