Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effect of dimensionality on the charge-density-wave in few-layers
  2H-NbSe$_2$   We investigate the charge density wave (CDW) instability in single and double
layers, as well as in the bulk 2H-NbSe$_{2}$. We demonstrate that the density
functional theory correctly describes the metallic CDW state in the bulk
2H-NbSe$_{2}$. We predict that both mono- and bilayer NbSe$_{2}$ undergo a CDW
instability. However, while in the bulk the instability occurs at a momentum
$\mathbf{q}_{CDW}\approx{2/3}\mathbf{\Gamma M}$, in free-standing layers it
occurs at $\mathbf{q}_{CDW}\approx{1/2}\mathbf{\Gamma M}$. Furthermore, while
in the bulk the CDW leads to a metallic state, in a monolayer the ground state
becomes semimetallic, in agreement with recent experimental data. We elucidate
the key role that an enhancement of the electron-phonon matrix element at
$\mathbf{q}\approx\mathbf{q}_{CDW}$ plays in forming the CDW ground state.

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The categories of this paper are: quant-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: adap-org
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The categories of this paper are: stat
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: q-bio