The paper by Oleg V. Yazyev and Steven G. Louie explores the electronic transport properties of polycrystalline graphene, focusing on the impact of grain boundaries on charge carrier transmission. Graphene, a two-dimensional form of carbon, is often found in polycrystalline form, and grain boundaries, as intrinsic topological defects, can significantly alter its electronic behavior. The authors develop a theory based on momentum conservation to predict two distinct transport behaviors: high transparency or perfect reflection of charge carriers over large energy ranges, depending on the grain boundary structure. They use first-principles quantum transport calculations to verify these predictions and investigate the effects of periodic grain boundaries with tunable transport gaps. The study highlights the potential for controlling charge currents in large-area graphene samples without introducing bulk band gaps, suggesting a pathway for practical graphene electronics. The research also discusses the importance of structural quality and disorder in grain boundaries, showing that moderate short-range charge defects can lead to low conductance in the transport gap, making it suitable for applications like field-effect transistors.The paper by Oleg V. Yazyev and Steven G. Louie explores the electronic transport properties of polycrystalline graphene, focusing on the impact of grain boundaries on charge carrier transmission. Graphene, a two-dimensional form of carbon, is often found in polycrystalline form, and grain boundaries, as intrinsic topological defects, can significantly alter its electronic behavior. The authors develop a theory based on momentum conservation to predict two distinct transport behaviors: high transparency or perfect reflection of charge carriers over large energy ranges, depending on the grain boundary structure. They use first-principles quantum transport calculations to verify these predictions and investigate the effects of periodic grain boundaries with tunable transport gaps. The study highlights the potential for controlling charge currents in large-area graphene samples without introducing bulk band gaps, suggesting a pathway for practical graphene electronics. The research also discusses the importance of structural quality and disorder in grain boundaries, showing that moderate short-range charge defects can lead to low conductance in the transport gap, making it suitable for applications like field-effect transistors.