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

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 ~2. The valley g-factor is highly tunable by vertical electric fields and reaches values in the range ~40-120. The results are quantitatively explained by a calculation considering topological magnetic moment and its dependence on confinement and the vertical displacement field.