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Published May 8, 2019 | Accepted Version
Journal Article Open

Quantum Enhancement of Charge Density Wave in NbS₂ in the Two-Dimensional Limit

Abstract

At ambient pressure, bulk 2H-NbS₂ displays no charge density wave instability, which is at odds with the isostructural and isoelectronic compounds 2H-NbSe₂, 2H-TaS₂, and 2H-TaSe₂, and in disagreement with harmonic calculations. Contradictory experimental results have been reported in supported single layers, as 1H-NbS₂ on Au(111) does not display a charge density wave, whereas 1H-NbS₂ on 6H-SiC(0001) endures a 3 × 3 reconstruction. Here, by carrying out quantum anharmonic calculations from first-principles, we evaluate the temperature dependence of phonon spectra in NbS₂ bulk and single layer as a function of pressure/strain. For bulk 2H-NbS₂, we find excellent agreement with inelastic X-ray spectra and demonstrate the removal of charge ordering due to anharmonicity. In the two-dimensional limit, we find an enhanced tendency toward charge density wave order. Freestanding 1H-NbS₂ undergoes a 3 × 3 reconstruction, in agreement with data on 6H-SiC(0001) supported samples. Moreover, as strains smaller than 0.5% in the lattice parameter are enough to completely remove the 3 × 3 superstructure, deposition of 1H-NbS₂ on flexible substrates or a small charge transfer via field-effect could lead to devices with dynamical switching on/off of charge order.

Additional Information

© 2019 American Chemical Society. Received: February 3, 2019; Revised: March 20, 2019; Published: April 1, 2019. R.B. acknowledges the CINECA award under the ISCRA initiative (Grant HP10BLTB9A). Computational resources were provided by PRACE (Project No. 2017174186) and EDARI (Grant A0050901202). I.E. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (Grant FIS2016-76617-P). M.C. acknowledges support from Agence Nationale de la Recherche under the reference No. ANR-13-IS10-0003-01. We acknowledge support from the Graphene Flagship (Grant Agreement 696656-GrapheneCore1 and 785219-GrapheneCore2). The authors declare no competing financial interest.

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Accepted Version - acs.nanolett.9b00504

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August 19, 2023
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