Title: Structural and electronic properties of germanene on MoS$_2$,
Abstract: To date, germanene has only been synthesized on metallic substrates. A
metallic substrate is usually detrimental for the two-dimensional Dirac nature
of germanene because the important electronic states near the Fermi level of
germanene can hybridize with the electronic states of the metallic substrate.
Here we report the successful synthesis of germanene on molybdenum disulfide
(MoS$_2$), a band gap material. Pre-existing defects in the MoS$_2$ surface act
as preferential nucleation sites for the germanene islands. The lattice
constant of the germanene layer (3.8 $\pm$ 0.2 \AA) is about 20\% larger than
the lattice constant of the MoS$_2$ substrate (3.16 \AA). Scanning tunneling
spectroscopy measurements and density functional theory calculations reveal
that there are, besides the linearly dispersing bands at the $K$ points, two
parabolic bands that cross the Fermi level at the $\Gamma$ point.