Emergence of orbital angular moment at van Hove singularity in graphene/h-BN moire superlattice

Bloch electrons lacking inversion symmetry exhibit orbital magnetic moments owing to the rotation around their center of mass; this moment induces a valley splitting in a magnetic field. For the graphene/h-BN moire superlattice, inversion symmetry is broken by the h-BN. The superlattice potential generates a series of Dirac points (DPs) and van Hove singularities (vHSs) within an experimentally accessible low energy state, providing a platform to study orbital moments with respect to band structure. In this work, theoretical calculations and magnetothermoelectric measurements are combined to reveal the emergence of an orbital magnetic moment at vHSs in graphene/h-BN moire superlattices. The thermoelectric signal for the vHS at the low energy side of the hole-side secondary DP exhibited significant magnetic field-induced valley splitting with an effective g-factor of approximately 130; splitting for other vHSs was negligible. This was attributed to the emergence of an orbital magnetic moment at the second vHS at the hole-side. An orbital magnetic moment emerges as a result of inversion symmetry broken at the graphene/h-BN moire superlattice. Here, Moriya et al. report thermoelectric evidence of magnetic field induced valley splitting for a van Hove singularity in this superlattice, suggesting the emergence of an orbital magnetic moment.