Quantum enhancement of charge density wave in NbS$_2$ in the 2D limit
Abstract
At ambient pressure, bulk 2H-NbS displays no charge density wave instability at odds with the isostructural and isoelectronic compounds 2H-NbSe, 2H-TaS and 2H-TaSe, and in disagreement with harmonic calculations. Contradictory experimental results have been reported in supported single layers, as 1H-NbS on Au(111) does not display a charge density wave, while 1H-NbS on 6H-SiC(0001) endures a reconstruction. Here, by carrying out quantum anharmonic calculations from first-principles, we evaluate the temperature dependence of phonon spectra in NbS bulk and single layer as a function of pressure/strain. For bulk 2H-NbS, we find excellent agreement with inelastic X-ray spectra and demonstrate the removal of charge ordering due to anharmonicity. In the 2D limit, we find an enhanced tendency toward charge density wave order. Freestanding 1H-NbS undergoes a reconstruction, in agreement with data on 6H-SiC(0001) supported samples. Moreover, as strains smaller than in the lattice parameter are enough to completely remove the superstructure, deposition of 1H-NbS on flexible substrates or a small charge transfer via field-effect could lead to devices with dynamical switching on/off of charge order.
Keywords
Cite
@article{arxiv.1902.00662,
title = {Quantum enhancement of charge density wave in NbS$_2$ in the 2D limit},
author = {Raffaello Bianco and Ion Errea and Lorenzo Monacelli and Matteo Calandra and Francesco Mauri},
journal= {arXiv preprint arXiv:1902.00662},
year = {2019}
}