Fig. 1: Experimental setup and Aharonov-Bohm oscillations.

a Schematic representation of the PN junction. The N region is depicted in blue, the P one in pink. Electrons are injected from the upper right ohmic contact by applying a bias voltage V_DC, and electron transmission T_MZ is measured at the lower left contact. b Left panel: T_MZ with respect to change ∆B of the magnetic field. Its oscillation period decreases as the interferometer length increases. Right panel: Schematic view of the Mach-Zehnder interferometer. At the beam splitters (dotted curves), mixing between the spin-up channels having opposite valley-isospin occurs. In the large interferometer, the beam splitters are formed at the intersections of the PN interface with the graphene edge. In the intermediate one, the top beam splitter is formed at the intersection with the edge, while the bottom splitter is at the intersection with the ν = 0 region in the bulk. In the small one, the two beam splitters are formed in the bulk. c T_MZ oscillations of the large interferometer plotted at different temperature. The absence of temperature dependence of the average T_MZ unambiguously ruled out the effect of the temperature on the intervalley scattering rate.