Observation of Landau Levels in Moiré-Patterned Graphene on Ru(0001) with Ar Bubbles Underneath

Liang-Wei Lan^1*, Bheim M. Llona¹, Swati Konijia¹, Prakash Gautam¹, Meng-Fan Luo², Chien-Cheng Kuo¹

¹Department of physics, National Sun Yat-sen University, Kaohsiung, Taiwan
²Department of Physics, National Central University, Jhongli, Taiwan

* Presenter:Liang-Wei Lan, email:lanlw1990@gmail.com

In the search for materials to observe quantum phenomena, graphene serves as a testing ground both for quantum field theory and condensed matter physics. Pristine graphene, a monolayer of carbon atoms in a honeycomb configuration, hosts Dirac fermions that are considered a wonder material [1]. In the study of graphene, physical surface deformation is believed to give rise to pseudo-magnetic fields. Recent reports tackled separately graphene with oxygen nanobubbles [2] and graphene with Moiré patterns [3, 4], both of which can induce an intrinsic pseudo-magnetic field (PMF). Hence, it is imperative to perform experiments combining these structures in one system to see its effect on the strength of the pseudo-magnetic field. Here, we prepare graphene with combined structures of Moiré patterns together with argon nanobubbles trapped on Ru(0001) substrate, where we observe the varying strength of pseudo-magnetic fields with the surface curvature. Through scanning tunneling microscopy (STM) and spectroscopy (STS), we visualize and detect obtrusive Landau level peaks on graphene with Moiré patterns and on the Moiré structures on top of argon nanobubbles surface. The observed spectroscopic peaks follow the E n relation. We further map out to profile and characterize the origin of the observed pseudo-magnetic field (PMF) by comparing it to the numerically calculated curvature-induced and strain-induced PMF for the nanobubbles Moiré structure graphene as well as for the density functional theory (DFT)-relaxed atomic model. Results indicate that the observed varying strength of the pseudo-magnetic field is induced by the varying strain on the surface of curved Moiré graphene on the Ru(0001) system offering a new platform for exploring quantum physical phenomena.

References:
[1] The graphene times. Nat. Nanotechnol. 14, 903 (2019).
[2] J. Lu, et. al., Nature Communications 3, 823 (2012).
[3] H. Shi, et.al., Nature Communications 11, 371 (2020).
[4] M. T. Mahmud and N. Sandler, Phys. Rev. B 102, 235410 (2020).

Keywords: Graphene, Ruthenium, Argon nanobubbles, Pseudo-magnetic field, Landau level