Spectroscopic imaging of Landau orbits in graphene using a scanning tunneling microscope

In strong magnetic fields, the kinetic energy is quenched and Dirac fermions in graphene form highly interacting quantized Landau levels. Spectroscopic mapping with the scanning tunneling microscope (STM) can be used to determine the orbital angular momentum for the non-degenerate Landau levels[1]. Following a similar approach, we examine lifting of the orbital degeneracy of the zeroth Landau level (ZLL) in the vicinity of charged impurities when the system is in an incompressible state. We observe that the orbital splitting in the single particle gaps follows a simple electrostatic model discussed in previous works[2], thereby allowing us to quantify the Coulomb potential induced by charged defects as well as the screening effect of the STM tip. Furthermore, we observe additional features in the symmetry breaking gaps of the ZLL that are not captured in the single-particle description and require further theoretical investigation. Our ability to image Landau orbits in a pristine graphene device paves the way for resolving the orbital splitting of the fractional quantum hall states and probing anyons in graphene in the quantum hall limit with the STM[3].

[1]B. Feldman et al. Science 354, 316–321(2016).

[2]A. Mayer et al. PRL 112, 036804(2014).

[3]Z. Papić et al. PRX 8, 011037(2018).