多原子半无限晶体中极化子的激发能量

研究多原子半无限晶体中电子与表面光学SO声子和体纵光学LO声子强耦合的极化子的激发态的性质。采用线性组合算符和幺正变换方法导出强耦合情形下极化子的基态能量、第一内部激发态能量和激发能量。结果表明,多原子半无限晶体中强耦合极化子的基态能量、第一内部激发态能量和激发能量不仅包含不同支LO声子和不同支SO声子与电子耦合的能量,而且还包含不同支LO声子之间和不同支SO声子之间相互作用贡献的附加能量。

Excitation Energy of the Polaron in a Polyatomic Semi-infinite Crystals

With the development of the solid theory and experimental technology,the properties of the surface polaron in a crystal have been of considerable interest.Many investigators studied the properties of the surface polaron in many aspects by a variety of theoretical and experimental methods.Sak and Evans et al.studied theoretically the surface polaron in polar crystals for the first time.Gu et al.discussed ideal surface polaron and the weak,the intermediate and the strong coupling polaron in semi-infinite polar crystal.The properties of the surface polaron in polar crystal and the effective mass of a slow-moving surface polaron in a semi-infinite crystal are investigated using perturbation and linear combination operator methods by the present authors and co-workers,respectively.However,the research of these methods only was restricted to the case of crystals having only one mode of the longitudinal optical(LO) phonon.A large number of polar crystals,with several atoms per unit cell,have more than one LO phonon branch.For example,in cuprite such as CuO₂ there are two LO phonon modes and for SiO₂,GaAs_1-xP_x and a large number materials with perovskites structure(SrTiO₃,LiNbO₃,BaTiO₃…) there are more than two modes.The polaron problem with many LO phonon branches has been studied by Matsura and Lepine.The properties of the polaron and the magnetopolaron in a polyatomic polar crystals are investigated by the present authors.However,so far,research of the properties of surface polaron in polyatomic crystals considering both the electron-bulk-longitudinal-optical(LO)-phonon and electron-surface-optical(SO)-phonon interaction,has been very scarce.The properties of the excited state of polaron in polyatomic semi-infinite crystal,which are the strong-coupling with bulk longitudinal optical phonon and surface optical phonon,are studied by using a linear combination operator and unitary transformation.Results show that when the election is infinitely close to the surface of the crystal,we can neglect the contribution of the LO phonons,otherwise,the distance between the election and the surface of the crystals is far more than the semi-diameter of the polaron;we must take into account the SO phonons effect,the LO phonons can be omitted.More commonly,when the distance between the election and surface is at the same magnitude grade of polaron's radii LO and so phonon's contribution must be studied at the same time.