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== Phonons in Perfect 4H-SiC
总共有 21 个声子模式。我们把它分成 18 个极性很小的和 3 个极性很强的两类
不同方向入射光的声子位置不同
声子的性质与它们在倒空间中的位置(即波矢)有关,而参与拉曼散射的声子波矢则由激光波长和拉曼入射配置(正入射、掠入射、边入射)决定。
在我们的实验(绿光)中,参与拉曼散射的声子都位于 Gamma 点附近(距离仅 xxx 埃),而与 Gamma 点的相对方向则根据入射配置而定。
对于正入射,声子大致位于 Gamma-A 线上;对于边入射,声子大致位于 Gamma-K 线上。对于掠入射,声子不位于任何高对称线上。
Properties of phonons depend on their positions in reciprocal space (i.e., wavevectors),
and the wavevectors of phonons participating in a Raman scattering process
are determined by the Raman experiment configuration.
In our experiments (back-scattering with 532 nm laser light),
phonons involved in Raman scattering are all located near the #sym.Gamma point
(about $5.13 times 10^(-3) angstrom$ from the #sym.Gamma point),
and their relative directions from the #sym.Gamma point depend on the incidence configurations.
For normal and edge incidence,
phonons participating in Raman process are approximately located along the #sym.GammaA and #sym.GammaK lines,
respectively, as illustrated in @figure-discont.
For grazing incidence, phonons are not located on any high-symmetry lines, and not shown in the figure.
#include "figure-discont.typ"
每个点都有 21 个声子模式。我们把它分成 18 个极性很小的和 3 个极性很强的两类。
对应于不同拉曼入射配置(正入射、掠入射、边入射)的声子位于倒空间中的不同位置。
它们都位于 Gamma 点附近,与 Gamma 点的距离由入射光波长决定,而与 Gamma 点的相对位置则由入射方向决定。
对于每一个 Gamma 附近的点,都有 21 个声子模式(简并模式按简并数计)。
我们将这 21 个声子模式分为两类18 个极性可以忽略的声子模式(即极性为零或非常弱的声子),在拉曼散射过程中它们的电极性造成的效应可以忽略;
3 个强极性声子模式,在拉曼光谱中电极性效应是可观测的。
@@ -24,6 +42,12 @@ These modes can be categorized into two groups:
这个分类是有意义的。从微观上讲,它也和原子的振动方向有关。
这个分类基于这样的事实:
4H-SiC 的原胞中,四个 Si 原子携带类似的正的 Born 有效电荷BEC
而四个 C 原子携带类似的负的 BEC @table-bec)。
18 个弱极性声子中,
两个 Si 原子的振动方向大致与另外两个 Si 原子相反,
C 原子也是如此,
导致宏观极性的抵消。
This classification is based on the fact that
the four Si atoms in the primitive cell of 4H-SiC carry similar positive Born effective charges (BECs),

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@@ -16,8 +16,6 @@ This approximation is widely adopted (cite) and justified by the fact that,
Therefore, negligible-polar phonons involved in Raman processes
have nearly indistinguishable properties from those at the #sym.Gamma point.
#include "figure-discont.typ"
gamma 点处 18 个声子的表示。它们的拉曼张量的形状可以确定,但大小无法确定。
// Representation of these 18 phonons, and the shape of their Raman tensors could be determined in advance.)

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- [ ] 英文
- [ ] 填充数据和引用
- [/] results
- [x] 总述
- [/] 总述
- [ ] 声子位置与实验对应
- [x] 中文
- [x] 英文
- [ ] 调整语言
- [ ] 调整画图
- [ ] 每个位置有 21 个模式
- [/] 无缺陷
- [ ] 总述
- [x] Gamma 附近有 21 个模式,我们将它们分为强极性和弱极性