Strong localization in suspended monolayer graphene by intervalley scattering

A gate-induced insulating behavior at zero magnetic field is observed in a high-mobility suspended monolayer graphene near the charge neutrality point. The graphene device initially cleaned by a current annealing technique underwent a thermopressure cycle to allow short-range impurities to be adsorbed directly by the ultraclean graphene surface. The adsorption process generated a strong temperature- and electric-field-dependent behavior on the conductance of the graphene device. The conductance around the neutrality point is observed to be reduced from around e(2)/h at 30 K to similar to 0.01 e(2)/h at 20 mK. A direct transition from an insulator to a quantum Hall conductor within approximate to 0.4 T accompanied by broken-symmetry-induced v = 0, +/- 1 plateaus confirms the presence of intervalley scatterers.