20 Electric transport and superconductivity in TransitionMetal Dichalcogenides nanolayers


CALL: 2013

DOMAIN: MS - Materials, Physics and Engineering





HOST INSTITUTION: University of Luxembourg


START: 2014-02-01

END: 2019-01-31

WEBSITE: https://www.uni.lu

Submitted Abstract

Bulk transition metal dichalcogenides (TMD) are layered materials and have long been studied in the past due to their remarkable properties. The phase diagram of metallic transition metal dichalcogenides (NbSe2, TiSe2 , TaS2, …) displays an interplay of charge density wave and superconductivity. Semiconducting TMD (MoS2, WS2, …) are cheap, have high electronic mobilities, and are highly flexible. As such they are a primary choice for flexible electronic devices. Recently, it has been demostrated that few-layers TMD can be synthesized either by exfoliation techniques or by laser thinning. These major achievements pave the way to the development of nanoscale electronic flexible devices based on few layers semiconducting TMD. Furthermore, the synthesis of single layers metallic TMD permits the investigation of the interplay between charge and superconducting order in low dimension. TMD are then at the heart of modern research in the field of nanotechnology as they are the new frontier 2D crystals beyond graphene. In this proposal, by using first principles calculations based on density functional theory and the GW approximation, we investigate the evolution of electric transport properties, optical and Raman spectra in going from bulk to single layer TMD.In semiconducting TMD we will develop a complete transport theory based on the Boltzman equation to describe the mobility of TMD nanodevices. We will consider both intrinsic (electron-phonon scattering) and extrinsic (effect of substrate) mechanisms affecting the mobility. The determination of the intrinsic mobility of dichalcogenides is a major advance as it sets a limitation on the quality and efficiency of TMD nanodevices. In metallic TMDs we will investigate the occurrence of charge order and superconductivity in going from bulk to one layer. Indeed, while nowadays there seems to be a fairly big consensus on the fact that in bulk TMDs the dominant mechanism for charge density wave is the electron-phonon interaction, it is unclear if superconductivity is phonon-mediated. Furthermore it is unclear if these phenomena survive in reduced dimension.Finally, we will also investigate metallic samples obtained from electrochemical doping of insulating few-layers TMD. Very recently it has been shown that electrochemical doping of MoS2 leads to superconductivity (Tc = 11K) in a sharp doping region. However, it is not known what is the mechanism at the origin of this phenomena and if other TMD nanolayers display a similar behavior. In this project, by merging the efforts of the Paris and Luxembourg groups, and relying on their complementarity, we will provide a full theoretical description of the physical properties of TMD in going from the bulk to the single layer. The experience of the Paris group in the field of electronphonon and anharmonicity joined with the capability of the Luxembourg group to describe the electron-electron interaction at the GW level will provide a reference theoretical framework to study nanomaterials with moderate correlation effects.

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