First principles analysis of the CDW instability of single-layer 1T-TiSe2 and its evolution with charge carrier density
Guster, Bogdan (Institut Català de Nanociència i Nanotecnologia)
Canadell Casanova, Enric 1950- (Institut de Ciència de Materials de Barcelona)
Pruneda, Miguel (Institut Català de Nanociència i Nanotecnologia)
Ordejon, Pablo (Institut Català de Nanociència i Nanotecnologia)

Data:	2018
Resum:	We present a density functional theory study of the electronic structure of single-layer TiSe, and focus on the charge density wave (CDW) instability present on this 2D material. We explain the periodicity of the CDW from the phonon band structure of the undistorted crystal, which is unstable under one of the phonon modes at the M point. This can be understood in terms of a partial band gap opening at the Fermi level, which we describe on the basis of the symmetry of the involved crystal orbitals, leading to an energy gain upon the displacement of the atoms following the phonon mode in a 2 × 1 structure. Furthermore, the combination of the corresponding phonons for the three inequivalent M points of the Brillouin zone leads to the 2 × 2 distortion characteristic of the CDW state. This leads to a further opening of a full gap, which reduces the energy of the 2 × 2 structure compared to the 2 × 1 one of a single M point phonon, and makes the CDW structure the most stable one. We also analyze the effect of charge injection into the layer on the structural instability. We predict that the 2 × 2 structure only survives for a certain range of doping levels, both for electrons and for holes, as doping reduces the energy gain due to the gap opening. We predict the transition from the commensurate 2 × 2 distortion to an incommensurate one with increasing wavelength upon increasing the doping level, followed by the appearance of the undistorted 1 × 1 structure for larger carrier concentrations.
Ajuts:	Agència de Gestió d'Ajuts Universitaris i de Recerca 2017/SGR-1506 European Commission 676598 Ministerio de Economía y Competitividad FIS2015-64886-C5-3-P Ministerio de Economía y Competitividad FIS2015-64886-C5-4-P Ministerio de Economía y Competitividad SEV-2015-0496 Ministerio de Economía y Competitividad SEV-2013-0295
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Matèria:	Charge density wave (CDW) ; Dichalcogenide ; Doping ; Phonon
Publicat a:	2D Materials, Vol. 5, Núm. 2 (March 2018) , art. 025024, ISSN 2053-1583

DOI: 10.1088/2053-1583/aab568

Post-print 13 p, 1.2 MB

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