  Mn$_{1-x}$Ga$_x$ (MnGa) with the $L1_0$ structure is a ferromagnetic material
with strong perpendicular magneto-crystalline anisotropy. Although MnGa thin
films have been successfully grown epitaxially and studied for various
spintronics devices, fundamental understandings of its electronic structure are
still lacking. To address this issue, we have investigated $L1_0$-MnGa thin
films using angle-resolved photoemission spectroscopy (ARPES). We have observed
a large Fermi surface with a rhombic shape in the $k_x$-$k_y$ plane overlapping
neighboring Fermi surfaces. The $k_z$ dependence of the band structure suggests
that the band dispersion observed by ARPES comes from the three-dimensional
band structure of MnGa folded by a $\sqrt{2} \times \sqrt{2}$ reconstruction.
The band dispersion across the corner of the rhombic Fermi surface forms an
electron pocket with a weak $k_z$ dependence. The effective mass and the
mobility of the bands crossing the Fermi level near the corner are estimated
from the ARPES images. Based on the experimental findings, the relationship
between the observed band structure and the spin-dependent properties in
MnGa-based heterostructures is discussed.
