Orbital Magnetism in Moiré Superlattices as revealed by Landau Level spectroscopy

Speaker: Paul Haney – NIST Gaithersburg

Host: Rembert Duine

Abstract:

A material’s response to magnetic fields provides a wealth of information about its properties, from the shape of its Fermi surface to detailed information about the topological properties of its electronic structure. Moiré materials offer a particularly interesting case study in this response, owing to their large lattice constant. In this work, we utilize local measurements of magnetic oscillations together with theoretical analysis of the magnetic response to determine the orbital magnetic properties of small-angle twisted double bilayer graphene (TDBG).

We perform gate-tuned scanning tunneling spectroscopy of the narrow Moiré minibands in TDBG in magnetic fields up to B = 15 T to fully map the bands with varying displacement fields. The high-resolution Landau level spectra reveal tunable electron- and hole-like pockets that deviate significantly in their magnetic response from the semiclassical model. This deviation is also analyzed by comparing the Hofstadter spectrum with the semiclassical result. The first-order correction in B is derived from the valley-contrasting orbital magnetic moment, and manifests as valley splitting of Landau levels. The second-order correction encodes the orbital magnetic susceptibility and is anomalously large – exceeding the first order correction for certain displacement fields. We show that the substantial contribution from the magnetic susceptibility is due to the large superlattice constants typical for Moiré materials.