APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022;
Chicago
Session Q65: Quantum Hall Effect: Transport Phenomena
3:00 PM–5:48 PM,
Wednesday, March 16, 2022
Room: Hyatt Regency Hotel -Grant Park C
Sponsoring
Unit:
DCMP
Chair: Frederic Joucken, Arizona State University
Abstract: Q65.00014 : Resonant States in Graphene QPCs in the Quantum Hall Regime
5:36 PM–5:48 PM
Abstract
Presenter:
Liam A Cohen
(University of California, Santa Barbara)
Author:
Liam A Cohen
(University of California, Santa Barbara)
Recent work has shown that bilayer graphene Van der Waals heterostructures host even denominator and other fractional quantum Hall states with energy gaps considerably larger than those observed in high mobility GaAs 2DEGs. However, a barrier to leveraging these intrinsic properties is the challenge of patterning local electrostatic potentials while preserving high mobility edge channels. In particular, both additive and subtractive nanofabrication processes tend to disorder the two dimensional electron layer in the regions of interest. In this talk, I will describe the fabrication and characterization of graphene quantum point contacts using pre-cut graphite split gates. By cutting the graphite top gate with AFM oxidation lithography, we are able to electrostatically define a highly tunable QPC that is directly integrated into a high mobility graphene based Van der Waals heterostructure. First, we demonstrate highly tunable transmission of multiple integer edge modes. We find that by increasing the electric field across these gates while keeping the bulk filing factor fixed, even split gate geometries with gaps as large as 180nm can pinch off all edge channels up to nu = 2. In addition, we observe resonant transmission deep in the pinch off regime. By studying the differential conductance of these resonant features we observe coulomb diamonds consistent with a quantum dot localized to the saddle point defined by the electrostatic gate potentials. These results suggest that resonant states can form in graphene QPCs via an entirely intrinsic mechanism in the absence of disorder in the channel. Understanding how these resonant states form, and how they may affect transmission in the fractional quantum Hall regime will be essential for future studies of edge state physics including Fabry-Perot interferometry, quasiparticle tunneling, and noise thermometry.