Using the superlattice (SL) eigenvalues $E_{μ,ν}^{c,v}$ and eigenfunctions $φ_{μν}^{c,v}(z) $, obtained within the theory of finite periodic systems, where $μ$ indicates the subbands and $ν$ the intra-subband levels, we calculate optical transitions in SLs and periodic systems. Based on the eigenfunction parity symmetries, studied in the previous paper, new symmetry selection rules (SSR) are derived and photoluminescence and infrared spectra for different types of SLs are calculated. The narrow peaks clustered in groups that couldn't be explained before in Nakamura's et al. for blue emitting devices, are now fully understood. Among the various properties and differences that we discuss in the paper, we notice that many transitions that were experimentally observed but theoretically forbidden, are now perfectly possible. Since the number of matrix-elements allowed by the SSR is generally too large, we devote the second part of this paper to show that one can obtain the same spectra when, besides the SSR, other leading order selection rules closely related to intra-subband symmetries are introduced. These rules reduce the number of matrix evaluations from $\sim n^2$$n_cn_v/2$ to $\sim n$$n_cn_v/2$, i.e., depending on the SL, from about 1000 to 100. We comment also on a third rule, that picks up the contributions of the surface and edge states, and show that it reduces further the number of transitions to $N_s\leq n_cn_v$. With these rules, the main peaks are conserved and their number practically matches with that of the actual spectrum. Excellent agreements with experimental results are found.
All-optical detection of periodic structure of chalcogenide superlattice using coherent folded acoustic phonons
硫系超晶格（SL）由GeTe和Sb $_{2}$ Te $_{3}$层的交替堆叠组成。该结构可以根据组成层的厚度变成3D拓扑绝缘体，使得SL周期的设计成为推进硫属化物SL作为自旋器件的潜在候选以及优化当前一代相变存储器器件的中心问题。在这里，我们探索的周期性结构的硫属化物SL观察相干折叠纵向声学（FLA）声子激发飞秒激光脉冲照射。FLA模式的峰值频率被观察到的GeTe层的厚度，这是很好地再现通过一个弹性连续模型的变化时的变化。此外，一个新的SL结构的样品组成的薄GeTe和Sb $_{2}$ Te $_{3}$层，这表明混合的Ge原子。这种基于相干FLA模式观察的全光学技术提供了原子分辨率的超晶格结构的非破坏性表征。
Guidelines for band gap opening in graphene superlattices with periodic π-vacancy distribution
Technische Universität Dresden（德累斯顿工业大学）；Center for Advanced System Understanding CASUS, Helmholtz-Zentrum Dresden-Rossendorf e. V.（亥姆霍兹德累斯顿-罗斯多夫中心高级系统理解中心）；Yonsei University（延世大学）
