Speaker-Vladimir Falko

Vladimir Falko
The University of Manchester, UK
Vladimir Falko is Director of the National Graphene Institute and Professor of Condensed Matter Theory at the University of Manchester. His career started with the PhD at the Institute for Solid State Physics RAS, followed by postdoctoral experience at Max-Planck-Institute in Stuttgart and Oxford University, and 19 years of service at Lancaster University. Falkowas responsible formany advances in the theory of localisation and quantum transport in mesoscopic systems,andhe made substantial contributions towards understanding of electronic and optical properties of graphene, including discovery of bilayer graphene.His current research interests include modelling of graphene-based electronic and optoelectronic systems and development of theories of electronic and optical properties of various atomically thin two-dimensional crystals and their heterostructures. His career has been marked by Humboldt Fellowship, EPSC Advanced Fellowship, ERC Advanced Investigator and Synergy Grants, and Royal Society Wolfson Foundation Research Merit Award.Falko played a pivotal role in building up the European research community in graphene and two-dimensional materials by setting the ‘Graphene Week’ conference series and by being one of the organisers and leaders of the European Graphene Flagship Project. From 2014, he is the founding Editor-in-Chief of the IoP Journal ‘2D Materials’ (with 2016 IF of 9.6).
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Abstract

Infraredand THz optics of atomically thin films of

transition-metaldichalcogenides

andpost-transition metal chalcogenides

Vladimir Fal’ko

National Graphene Institute, University of Manchester, Manchester, UK

Transition-metaldichalcogenides (TMD), MoS2, MoSe2, WS2 andWSe2 and post-transition metal chalcogenides (PTMC), InSe and GaSeare materials where a strong covalent bonding of atoms inside individual layerscoexists with a weak van der Waals coupling of the consecutive layer of thebulk crystal. Such peculiar bonding makes it possible to isolate mechanically,or to grow epitaxially atomically thin films of such compounds with a precise numberof atomic layers. At the same time, van der Waals nature of these crystalscoexists with strong hybridizations of – separately – conduction and valenceband orbitals in the consecutive monolayers in the film, making the bandstructure of few-layer atomically thin TMDs and PTMCs sensitive to the numberof layers in them. In particular, few-layer films acquire multiple subbands intheir electronic spectra, with a strong coupling of inter-subband transitionsof carriers (electrons in n-doped and holes in p-doped materials) without-of-plane polarised photons. Here, we show that, when n- or p-doped,few-layer films of TMDs and PTMCs become absorbers and emitters of infrared(IR) and THz light. Our density functional theory modelling and a speciallydesigned hybrid k·p theory for the monolayers of thesematerials, combined with the tight-binding model description of the interlayerhopping (HkpTB), predicts that optical activity of few-layer films of these twoclasses of compounds densely covers the range from IR (1.5 micron) for bilayerfilms to THz for the films with 3-10 layers. In a way, these thin films areanalogous to quantum wells in conventional semiconductors, and, by choosing thenumber of layers, and/or n- or p-doping in one of TMD and PTMC compounds, onecan tune such inter-subband transition energy to the desirable applicationrange, offering a new way how 2D materials can be harnessed for developing newtechnologies.


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