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Tunable Valley Splitting due to Topological Orbital Magnetic Moment in Bilayer Graphene Quantum Point Contacts

In multivalley semiconductors, the valley degree of freedom can be potentially used to store, manipulate and read quantum information, but its control remains challenging. The valleys in bilayer graphene can be addressed by a perpendicular magnetic field which couples by the valley g-factor. However, control over the valley g-factor has not been demonstrated yet. We experimentally determine the energy spectrum of a quantum point contact realized by a suitable gate geometry in bilayer graphene. Using finite bias spectroscopy we measure the energy scales arising from the lateral confinement as well as the Zeeman splitting and find a spin g-factor of 2. The valley g-factor can be tuned by a factor of 3 using vertical electric fields, reaching values between 40 and 120. The results are quantitatively explained by a calculation considering topological magnetic moment and its dependence on confinement and the vertical displacement field.