By Dr. Samuel Magorrian, National Graphene Institute in Manchester, UK
We present the analysis of electronic band structure of InSe and GaSe films, from the stoichiometric mono- to N-layer films, and we describe the resulting optical properties of these 2D materials [1,2] and conduction/valence band parameters. This study is based on the ab initio DFT and related multi-orbital tight-binding model analysis of the electronic band structure and wave functions in the two-dimensional N-layer InSe crystals, and it is compared to the results of ARPES and luminescence spectroscopy of this material. We show [1-3] that the band gap in InSe (and GaSe) strongly depend on the number of layers, with a strong (more than twice) reduction from the monolayer to crystals with N>6. We find that the conduction-band-edge electron mass in few-layer InSe is quite light (comparable to Si), which suggests opportunities for high-mobility devices and the development of nanocircuits. In contrast, the valence band in mono-, bi- and trilayer InSe is flat, opening possibilities for strongly correlated hole gases in p-doped films. Using the band structure and wave functions, we analyse optical transitions in thin films of InSe and GaSe, identify their polarisation and compare the results of modelling to the measurements performed on hBN-encapsulated atomically thin InSe and GaSe crystals. Then, we show that the same materials have potential for optical functionality in the far infrared range, for which one can exploit the intersubband transitions in InSe and GaSe few-layer films.
 D. Bandurin, A. Tyurnina, G. Yu, A. Mishchenko, V. Zólyomi, S. Morozov, R. Kumar, R. Gorbachev, Z. Kudrynskyi, S. Pezzini, Z. Kovalyuk, U. Zeitler, K. Novoselov, A. Patanè, L. Eaves, I. Grigorieva, V. Fal’ko, A. Geim, Y. Cao, Nature Nanotechnology 12, 223–227 (2017)
 Magorrian, S., Zolyomi, V., Falko V. , Phys. Rev. B 94, 245431 (2016); S. J. Magorrian, V. Zolyomi, V. I. Fal’ko, Phys. Rev. B 96, 195428 (2017); Zolyomi, N Drummond, V.I. Fal’ko, Phys Rev B 89, 205416 (2014); V. Zolyomi, N. Drummond, V.I. Fal’ko, Phys. Rev. B 87, 195403 (2013)
 Mudd, G. W., Molas, M. R., Chen, X., Zólyomi, V., Nogajewski, K., Kudrynskyi, Z. R., Kovalyuk, Z. D., Yusa, G., Makarovsky, O., Potemski, M., Fal’ko, V. & Patanè, A., Scientific Reports. 6, 39619 (2016)
Dr. Samuel Magorrian is a theoretical physicist working in the field of Condensed Matter theory. He obtained his PhD from the University of Manchester, UK, and is based at the National Graphene Institute in Manchester. His current research interests focus on the theory of the electronic and optical properties of 2D materials in the family of III-VI hexagonal layered crystals, such as InSe and GaSe, and the development of scalable models to predict their properties and uses in new technologies.