  Dirac materials, which feature Dirac cones in the reciprocal space, have been
one of the hottest topics in condensed matter physics in the past decade. To
date, 2D and 3D Dirac Fermions have been extensively studied, while their 1D
counterparts are rare. Recently, Si nanoribbons (SiNRs), which are composed of
alternating pentagonal Si rings, have attracted intensive attention. However,
the electronic structure and topological properties of SiNRs are still elusive.
Here, by angle-resolved photoemission spectroscopy, scanning tunneling
microscopy/spectroscopy measurements, first-principles calculations, and
tight-binding model analysis, we demonstrate the existence of 1D Dirac Fermions
in SiNRs. Our theoretical analysis shows that the Dirac cones derive from the
armchairlike Si chain in the center of the nanoribbon and can be described by
the Su-Schrieffer-Heeger model. These results establish SiNRs as a platform for
studying the novel physical properties in 1D Dirac materials.
