  We present ALMA continuum observations at a wavelength of 1.25 mm of the
debris disk surrounding the $\sim$ 100 Myr old solar analog HD 107146. The
continuum emission extends from about 30 to 150 AU from the central star with a
decrease in the surface brightness at intermediate radii. We analyze the ALMA
interferometric visibilities using debris disk models with radial profiles for
the dust surface density parametrized as i) a single power-law, ii) a single
power-law with a gap, and iii) a double power-law. We find that models with a
gap of radial width $\sim 8$ AU at a distance of $\sim 80$ AU from the central
star, as well as double power-law models with a dip in the dust surface density
at $\sim 70$ AU provide significantly better fits to the ALMA data than single
power-law models. We discuss possible scenarios for the origin of the HD 107146
debris disk using models of planetesimal belts in which the formation of
Pluto-sized objects trigger disruptive collisions of large bodies, as well as
models which consider the interaction of a planetary system with a planetesimal
belt and spatial variation of the dust opacity across the disk. If future
observations with higher angular resolution and sensitivity confirm the
fully-depleted gap structure discussed here, a planet with a mass of
approximately a few Earth masses in a nearly circular orbit at $\sim 80$ AU
from the central star would be a possible explanation for the presence of the
gap.
