多原子半无限晶体中表面极化子的内部激发态

研究多原子半无限晶体中电子与表面光学(SO)声子耦合强,而与体纵光学(LO)声子耦合弱的极化子的激发态性质.采用线性组合算符和幺正变换方法导出与SO声子耦合强而与LO声子耦合弱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与SO声子耦合强,而与LO声子耦合弱的极化子的基态能量、第一内部激发态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,而且也包含不同支SO声子之间相互作用贡献的附加能量.激发能量与体纵光学声子无关.

Internal Excited State of Surface Polaron in Polyatomic Semi-infinite Crystals

With the development of the material science and experimental technology,the properties of the surface polaron in semi-infinite crystals have been of considerable interest.Many investigators studied the properties of surface polaron in semi-infinite crystals in many aspects by a variety of theoretical and experimental methods. Most polar crystals are diatomic and cubic and their crystal structure belongs to NaCl,CsCl or ZnS type. In these crystals there is one longitudinal optical (LO) phonon mode.The properties of crystals having only one LO phonon branch have been studied by a great variety of techniques.However,a large number of polar crystals,with several atoms per unit cell,have more than one LO phonon branch.For example,in cuprite compounds such as CuO₂/there are two LO phonon modes.SiO₂,GaAs_1-xP_x and a large number of perovskite’s crystals (SrTiO₃,LiNbO₃,BaTiO₃,etc) have more than two LO phonon modes.The pelaron problem with many LO phonon branches has been studied by Matsura and Lepine.The properties of the polaron and the magneto-pelaron in a polyatomic polar crystals are investigated by the present authors.However,so far,research of the properties of surface polaron in polyatomic semi-infinite crystals considering both the electron-bulk-longitudinal optical-phonon and electron-surface-optical-phonon interaction,has been very scarce.Recently,the properties of the excited state of surface polaron in polyatomic semi-infinite,which are the strong-coupling with surface optical phonon and the bulk longitudinal optical phonon,are studied by using a linear-combination operator and unitary transformation method by the present authors. For the bulk polaron,the weak and intermediate coupling theories are applicable for electron-bulk LO phonon coupling constant α_L<6,whereas for the surface polaron,this confinement is about 2.5.Hence, when the electron-SO phonon coupling constant satisfied α_s>2.5,the strong-coupling theory must be applied. There is a weak coupling between the electron and the bulk LO phonon,but a strong coupling between the electron and the SO phonon for many polar crystals.So far,the research of this aspect is very scarce. The properties of the excited state of surface polaron in polyatomic semi-infinite crystal,which are the strong-coupling with surface optical phonon and the weak-coupling with bulk longitudinal optical phonon,are studied by using a linear combination operator and unitary transformation method.Results show that the ground state energy and the first internal excited state energy of surface pelaron in polyatomic semi-infinite crystal, which are the strong-coupling with surface optical phonon and the weak-coupling with bulk longitudinal optical phonon not only includes the coupling contribution between electron with different LO phonon and SO phonon branches,but also exists only an extra contribution due to crossed terms between the different SO phonon bran-ches,and the excitation energy not only includes the coupling contribution between electron and different SO phonon branches,but also exists only an extra contribution due to crossed terms between the different SO phonon branches.The excitation energy is independent of the bulk longitudinal optical phonon.