Understanding Disorder in Monolayer Graphene Devices with Gate-Defined Superlattices
arxiv(2024)
摘要
Engineering superlattices (SLs) - which are spatially periodic potential
landscapes for electrons - is an emerging approach for the realization of
exotic properties, including superconductivity and correlated insulators, in
two-dimensional materials. While moiré SL engineering has been a popular
approach, nanopatterning is an attractive alternative offering control over the
pattern and wavelength of the SL. However, the disorder arising in the system
due to imperfect nanopatterning is seldom studied. Here, by creating a square
lattice of nanoholes in the SiO_2 dielectric layer using nanolithography, we
study the superlattice potential and the disorder formed in hBN-graphene-hBN
heterostructures. Specifically, we observe that while electrical transport
shows distinct superlattice satellite peaks, the disorder of the device is
significantly higher than graphene devices without any SL. We use
finite-element simulations combined with a resistor network model to calculate
the effects of this disorder on the transport properties of graphene. We
consider three types of disorder: nanohole size variations, adjacent nanohole
mergers, and nanohole vacancies. Comparing our experimental results with the
model, we find that the disorder primarily originates from nanohole size
variations rather than nanohole mergers in square SLs. We further confirm the
validity of our model by comparing the results with quantum transport
simulations. Our findings highlight the applicability of our simple framework
to predict and engineer disorder in patterned SLs, specifically correlating
variations in the resultant SL patterns to the observed disorder. Our combined
experimental and theoretical results could serve as a valuable guide for
optimizing nanofabrication processes to engineer disorder in nanopatterned SLs.
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