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Coexistence of Elastic Modulations in the Charge Density Wave State of 2H-NbSe2

Coexistence of Elastic Modulations in the Charge Density Wave State of 2H-NbSe2

Scientific Highlights Materials for information science and electronics 28 May 2019 574 hits icmabcsic
Bogdan GusterCarmen Rubio-VerdúRoberto RoblesJavier ZaldívarPaul DreherMiguel PrunedaJosé Ángel Silva-GuillénDeung-Jang ChoiJosé I. PascualMiguel M. Ugeda*Pablo Ordejón*, and Enric Canadell*.  Nano Lett., 2019, 19 (5), pp 3027–3032.

DOI: 10.1021/acs.nanolett.9b00268

Bulk and single-layer 2H-NbSe2 exhibit identical charge density wave order (CDW) with a quasi-commensurate 3 × 3 superlattice periodicity. Here we combine scanning tunnelling microscopy (STM) imaging at T = 1 K of 2H-NbSe2 with first-principles density functional theory (DFT) calculations to investigate the structural atomic rearrangement of this CDW phase. Our calculations for single-layers reveal that six different atomic structures are compatible with the 3 × 3 CDW distortion, although all of them lie on a very narrow energy range of at most 3 meV per formula unit, suggesting the coexistence of such structures. Our atomically resolved STM images of bulk 2H-NbSe2 unambiguously confirm this by identifying two of these structures. Remarkably, these structures differ from the X-ray crystal structure reported for the bulk 3 × 3 CDW which in fact is also one of the six DFT structures located for the single-layer. Our calculations also show that due to the minute energy difference between the different phases, the ground state of the 3 × 3 CDW could be extremely sensitive to doping, external strain or internal pressure within the crystal. The presence of multiphase CDW order in 2H-NbSe2 may provide further understanding of its low temperature state and the competition between different instabilities.

Coexistence of Elastic Modulations in the Charge Density Wave State of 2H-NbSe2

 

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