Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Layer-dependent anisotropic electronic structure of freestanding
  quasi-two-dimensional MoS$_2$   The anisotropy of the electronic transition is a well-known characteristic of
low-dimensional transition-metal dichalcogenides, but their layer-thickness
dependence has not been properly in- vestigated experimentally until now. Yet,
it not only determines the optical properties of these low-dimensional
materials, but also holds the key in revealing the underlying character of the
elec- tronic states involved. Here we used both angle-resolved electron
energy-loss spectroscopy and spectral analysis of angle-integrated spectra to
study the evolution of the anisotropic electronic transition involving the low
energy valence electrons in the freestanding MoS$_2$ layers with different
thicknesses. We are able to demonstrate that the well-known direct gap at 1.8
eV is only excited by the in-plane polarized field while the out-of-plane
polarized optical gap is 2.4$\pm$0.2 eV in monolayer MoS$_2$. This contrasts
with the much smaller anisotropic response found for the indirect gap in the
few-layer MoS$_2$ systems. In addition, we determined that the joint density of
states associated with the indirect gap transition in the multilayer systems
and the corresponding indirect transition in the monolayer case has a
characteristic three-dimensional-like character. We attribute this to the
soft-edge behavior of the confining potential and it is an important factor
when considering the dynamical screening of the electric field at the relevant
excitation energies. Our result provides a logical explanation, for the large
sensitivity of the indirect transition to thickness variation compared with
that for the direct transition, in terms of quantum confinement.

23
The categories of this paper are: solv-int
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The categories of this paper are: eess
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: stat
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom