将经典的表示理论移动到附录

paper/appendix/representation/default.typ

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+== Symmetry Analysis of Phonons in 4H-SiC
+
+The phonons at the #sym.Gamma point in 4H-SiC (space group P6#sub[3]mc)
+  corresponds to four irreducible representations of C#sub[6v] point group
+  (4A#sub[1] + 4B#sub[1] + 4E#sub[1] + 4E#sub[2]),
+  including translational movement (1A#sub[1] + 1E#sub[1]), strong polar modes (1A#sub[1] + 1E#sub[1]),
+  and negligible-polar modes (2A#sub[1] + 4B#sub[1] + 2E#sub[1] + 4E#sub[2]).
+The form of the Raman tensors for each representation is well known and summarized in @table-rep.
+
+#include "table-rep.typ"
+
+By further decomposing the doubly degenerate modes (E#sub[1] and E#sub[2] of C#sub[6v] group)
+  into the C#sub[2v] point group,
+  the raman scattering corresponding to vibration along x and y directions could be distinguished.
+For example, the E#sub[2] peeks observed in the Raman experiment of z(yy)#overline[z]
+    correspond to phonons vibrating along the y direction,
+  while the E#sub[2] peeks observed in z(yx)#overline[z] correspond to phonons vibrating along the x direction.
+This is important when the x and y directions become inequivalent and the double degeneracies are slightly lifted.