极性晶体中极化子效应对界面强耦合激子性质的影响

在Huybrechts关于强耦合极化子的模型基础上,采用LLP变分法研究了极性晶体中激子与IO声子强耦合、与LO声子弱耦合体系的基态能量,推导出了激子的自陷能和诱生势的表达式,并以AgCl/AgBr晶体为例进行了数值计算,结果表明,激子的自陷能不仅与激子的坐标z有关,而且电子-空穴间距离ρ对激子自陷能的影响也十分显著;激子的诱生势不仅与电子-空穴间距离ρ有关,而且激子距离晶体界面的位置z对诱生势的影响也十分显著.

The Influence of Polaron Effects on the Properties of the Strong-coupling Interface Exciton in Polar Crystals

Based on model of Huybrechts strong-coupling polaron, the ground state energy of the system, in which the excitons interact with both the weak-coupling bulk longitudinal-optical (LO) phonons and strong-coupling interface-optical (IO) phonons in a polar crystal, is studied by using the Lee-Low-Pines variational method, the self-trapping energy and the induced potential of the excitons are derived. The results are shown as following:1. The self-trapping energy of the excitons is composed of two parts. One part is the polaron effects resulting from the exciton-LO phonon interaction, the other part is induced by the exciton-IO phonon interaction. The self-trapping energy Etre,h-LO, which is produced by the interaction between the exciton and LO-phonon, will increase with increasing the coordinate z, it tends to a constant finally. The self-trapping energy Etre,h-IO, which is induced by the interaction between the exciton and IO-phonon, will increase with decreasing the coordinate, especially near the interface, the decrease in z will lead to drastic increase in Etre,h-IO. It is indicated that near the interface, the contribution of the electron-IO phonon interaction to the self-trapping energy of the excitons is dominant, whereas the exciton in the bulk far from the interface, the contribution of the electron-LO phonon interaction to the self-trapping energy of exciton is dominant. The influence of the distance ρ between the electron and hole on the self-trapping energy Etre,h-IO is also remarkable. Etre,h-IO will increase with increasing ρ. With ρ increasing, the decrease in coordinate z will lead to drastic increase in Etre,h-IO. 2. The induced potential of the excitons is also composed of two parts, one part is the polaron effects produced by the interaction between the exciton and LO phonons, the other part is induced by the exciton-IO phonon interaction. The variation law of the induced potential Ve,h-LO and Ve,h-IO resulting from the exciton-LO phonon and exciton-IO phonon interaction, respectively, is agreement with the variation law of the induced potential produced by the weak-coupling exciton-LO phonon interaction in 3D polar crystal and the strong-coupling exciton-SO phonon interaction in 2D polar crystal respectively. The influence of the coordinate of the exciton on the induced potential Ve,h-IO and Ve,h-IO is notable.Ve,h-LO increases with increasing the coordinate z. With z increasing, the increase in the distance ρ between the electron and hole will lead to drastic decrease in Ve,h-LO. The induced potential Ve,h-IO decreases with increasing z. With z decreasing, the decrease in ρ will lead to drastic increase in induced potential Ve,h-IO. The results show that the influence of the surface and interface phonon in polar crystal can not be neglected. It is especially important for the polar slab, quantum well and heterostructures, in which the carriers are both strong-coupling with surface or interface optical phonon and weak-coupling with bulk longitudinal optical phonon.