Quantum Enhancement of Charge Density Wave in NbS<sub>2</sub> in the Two-Dimensional Limit.
basic_science · Level V
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- Record sourced from PubMed, PMID 30932501.
- Also identified by DOI 10.1021/acs.nanolett.9b00504.
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Abstract
At ambient pressure, bulk 2H-NbS<sub>2</sub> displays no charge density wave instability, which is at odds with the isostructural and isoelectronic compounds 2H-NbSe<sub>2</sub>, 2H-TaS<sub>2</sub>, and 2H-TaSe<sub>2</sub>, and in disagreement with harmonic calculations. Contradictory experimental results have been reported in supported single layers, as 1H-NbS<sub>2</sub> on Au(111) does not display a charge density wave, whereas 1H-NbS<sub>2</sub> 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 NbS<sub>2</sub> bulk and single layer as a function of pressure/strain. For bulk 2H-NbS<sub>2</sub>, 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-NbS<sub>2</sub> 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-NbS<sub>2</sub> on flexible substrates or a small charge transfer via field-effect could lead to devices with dynamical switching on/off of charge order.