闪锌矿结构链中的非线性表面局域模

利用数值计算研究了近邻原子质量和作用力常数均不同的一维链中的非线性表面局域模,该模型模拟闪锌矿结构晶体中〈111〉方向一列表面原子的非线性振动.在考虑近邻原子间相互作用势函数中的四次方非线性项后,在相应线性系统频带的禁带中和光学支上面发现了非线性表面局域模(S1模和S2模).在考虑近邻原子间相互作用势函数中的三次方和四次方非线性项时,非线性表面局域模中出现静态"直流"分量,表面局域模振动频率降低.结果还表明在相应线性系统频带的光学支上面和禁带中是否存在非线性表面局域模与三次方、四次方非线性项和最大的可能达到的位移有关.

Nonlinear Surface Modes in an Anharmonic Sphalerite-Structure Lattice

We study nonlinear vibrational localized surface modes in one dimensional diatomic chain with different masses and alternating force constants between nearest neighbors by numerical calculation. This model anharmonicity in the nearest-neighbor interaction potential produce localized surface mode (S1 mode) with frequency close to the acoustic branch in the gap and localized surface modes (S2 mode) with frequency above the top of the optical branch. With the cubic term, the frequency of the mode lowers and the static displacement appears. Our work also shown that whether localized surface excitations can be found in the range of the frequency of the gap or just above the top of the optical branch is related to the balance between the cubic and the quartic anharmonicity, and to the maximum attainable displacement.