43 lines
2.6 KiB
XML
43 lines
2.6 KiB
XML
== Phonons in Perfect 4H-SiC
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不同方向入射光的声子位置不同。我们只研究 Gamma 附近的那些。
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参与拉曼散射的声子的波矢等于入射光与散射光的波矢差。
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因此，在我们的实验（绿光和紫外光的背散射）中，参与拉曼散射的声子都位于 Gamma 点附近，且不同的入射方向对应的声子波矢不同。
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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。
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The wavevectors of phonons participating in Raman scattering
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equal to the difference between the wavevectors of the incident and scattered light.
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Thus, in our experiments (back-scattering with green and UV light),
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the phonons involved are located very close to the #sym.Gamma point,
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with various wavevectors determined by the incidence configurations.
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As illustrated in @figure-discont, in Raman experiments of normal and edge incidence,
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the relevant phonons lie approximately at the #sym.Gamma–A and #sym.Gamma–K lines, respectively.
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For grazing incidence,
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the relevant phonons do not reside on any high-symmetry lines and are therefore not depicted in the figure.
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#include "figure-discont.typ"
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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。
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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）。
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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；
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和 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。
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At each position near the #sym.Gamma point, there are 21 phonon modes with non-zero frequency (counting degeneracies).
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These phonons were categorized into two groups according to their electrical polarities:
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18 negligible-polar phonons (i.e., zero or very weak electrical polarity),
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where atoms of the same species vibrate in opposite directions,
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resulting in effective cancellation of electrical polarization during the Raman process
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(gray lines in @figure-discont);
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and three strong-polar phonons,
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where atoms of the same species vibrate in phase,
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resulting in strong electrical polarization and observable effects in Raman spectra
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(colored lines in @figure-discont).
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The categorized is also illustrated and compared with Raman experiment in @fig-raman.
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#include "figure-raman.typ"
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#include "non-polar/default.typ"
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#include "polar/default.typ"
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