The paper by Rycer, Tworzydlo, and Beenakker explores the valley filter and valley valve in graphene. They demonstrate that a nonequilibrium valley polarization can be achieved in a graphene sheet by injecting current through a ballistic point contact with zigzag edges. The valley polarization can be inverted by applying a gate voltage to the point contact region. Two valley filters in series can function as an electrostatically controlled "valley valve," similar to a spin valve but without the need for magnetic fields. The authors use a tight-binding model to simulate the behavior of the valley filter and valley valve, showing that the valley polarization can be over 95% when the Fermi level lies above the Dirac point. This research highlights the potential of valleytronics in carbon electronics, where the valley degree of freedom can be used to control electronic devices.The paper by Rycer, Tworzydlo, and Beenakker explores the valley filter and valley valve in graphene. They demonstrate that a nonequilibrium valley polarization can be achieved in a graphene sheet by injecting current through a ballistic point contact with zigzag edges. The valley polarization can be inverted by applying a gate voltage to the point contact region. Two valley filters in series can function as an electrostatically controlled "valley valve," similar to a spin valve but without the need for magnetic fields. The authors use a tight-binding model to simulate the behavior of the valley filter and valley valve, showing that the valley polarization can be over 95% when the Fermi level lies above the Dirac point. This research highlights the potential of valleytronics in carbon electronics, where the valley degree of freedom can be used to control electronic devices.