We present the results of an infrared spectroscopy study of topological insulators Bi(2)Se(3), Bi(2)Te(3) and Sb(2)Te(3). Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi(2)Se(3), whereas in Bi(2)Te(3) and Sb(2)Te(3) it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature.

Literature describing X-ray photoelectron spectroscopy (XPS) generally assumes that the reader will understand why the method cannot detect hydrogen atoms. On the other hand, students struggle finding the answer even after extensive literature search and reading.

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We present results from light scattering experiments on tetragonal FeS with the focus placed on lattice dynamics. We identify the Raman active A1g and B1g phonon modes, a second order scattering process involving two acoustic phonons, and contributions from potentially defect-induced scattering. The temperature dependence between 300 and 20 K of all observed phonon energies is governed by the lattice contraction. Below 20 K the phonon energies increase by 0.5-1 cm −1 thus indicating putative short range magnetic order. Along with the experiments we performed latticedynamical simulations and a symmetry analysis for the phonons and potential overtones and find good agreement with the experiments. In particular, we argue that the two-phonon excitation observed in a gap between the optical branches becomes observable due to significant electronphonon interaction.

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When single crystals are probed by powder X-ray diffraction (PXRD) systems, the peak widths are smaller and signal intensities are greater than those from powdered samples. Instead of the expected single peak, a doublet can be observed, and undergraduate students face a big challenge explaining its origin. This activity is suitable as an inquiry-based, upper-level undergraduate laboratory activity. Students typically engage in an extensive literature search and reading in order to understand observed diffraction data. With a little bit of guidance from the instructor, students can learn how X-rays are generated, and which X-rays are used in PXRD experiments. They can also learn about the electronic transitions in the target electrode leading to characteristic X-rays and learn about the role of spin–orbit coupling.

We discuss how a powder X-ray diffraction (XRD) system can be used to probe large pyrite (FeS2) crystals to reveal a peak generally not documented in the literature. The ability to detect this peak is attributed to the use of a large crystal, which gives large signal intensities. This type of experiment provides a research-like experience and gives students the opportunity to deepen their understanding of diffraction orders. In this experiment students are first challenged to be creative and determine how to mount a mineral crystal in a powder XRD system and then practice critical thinking in order to determine the origin of the unknown XRD peak. This experiment may also be generalized to crystals other than pyrite.