Quantum enhancement of charge density wave in NbS$_2$ in the 2D limit

Raffaello Bianco; Ion Errea; Lorenzo Monacelli; Matteo Calandra; Francesco Mauri

doi:10.1021/acs.nanolett.9b00504

paper

Quantum enhancement of charge density wave in NbS $_{2}$ in the 2D limit

arXiv:1902.00662 · doi:10.1021/acs.nanolett.9b00504

Abstract

At ambient pressure, bulk 2H-NbS $_{2}$ displays no charge density wave instability at odds with the isostructural and isoelectronic compounds 2H-NbSe $_{2}$ , 2H-TaS $_{2}$ and 2H-TaSe $_{2}$ , and in disagreement with harmonic calculations. Contradictory experimental results have been reported in supported single layers, as 1H-NbS $_{2}$ on Au(111) does not display a charge density wave, while 1H-NbS $_{2}$ on 6H-SiC(0001) endures a $3 \times 3$ reconstruction. Here, by carrying out quantum anharmonic calculations from first-principles, we evaluate the temperature dependence of phonon spectra in NbS $_{2}$ bulk and single layer as a function of pressure/strain. For bulk 2H-NbS $_{2}$ , 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 $_{2}$ undergoes a $3 \times 3$ 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 $3 \times 3$ superstructure, deposition of 1H-NbS $_{2}$ on flexible substrates or a small charge transfer via field-effect could lead to devices with dynamical switching on/off of charge order.

Quantum enhancement of charge density wave in NbS $_{2}$ in the 2D limit

Abstract

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Quantum enhancement of charge density wave in NbS2​ in the 2D limit

Abstract

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Quantum enhancement of charge density wave in NbS $_{2}$ in the 2D limit