Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 55: Graphene and 2D Materials (joint session TT/HL)

HL 55.8: Talk

Thursday, March 20, 2025, 17:00–17:15, H33

Landau level mixing in moderately disordered graphene junctions — •Yu-Ting Hsiao and Ming-Hao Liu — Department of Physics,National Cheng Kung University,Tainan 70101,Taiwan

Landau levels are quantized eigenenergy levels in two-dimensional (2D) systems in the presence of an applied perpendicular magnetic field. They are the basic origin of the (integer) quantum Hall effect (QHE). To observe the QHE, i.e., electrical conductance quantized into a sequence of an integer multiple of the universal conductance quantum e²/h, the sample quality and the strength of the magnetic field typically play the most decisive roles. The cleaner the sample, the weaker the magnetic field required to form the Landau levels. Collaborating with the experiment group led by Prof. Wei Yang from the Institute of Physics(CAS), China, who observed phase shifts of quantized conductance plateaus in ultraclean two-terminal, single-gated graphene devices. From our quantum transport simulations with a systematic tuning of different parameters that could influence the conductance behavior of the graphene device, we found that the experimentally observed phase shift shall arise from the mixing of Landau levels across two neighboring regions with slightly different doping concentrations. Interestingly, we found that the Landau level mixing occurs only when the graphene sample is moderately disordered. In the purely ballistic regime or under strong disorder, the Landau levels mixing fails to form. Our finding reveals a counter-intuitive role played by disorder, possibly also required in other fundamental transport phenomena, such as the Shubnikov-de Haas oscillation.

Keywords: quantum transport; phase transition