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T. Fabian, F. Libisch:
"Universal conductance and shot noise fluctuations in graphene";
Poster: IWEPNM 2020, Kirchberg in Tirol; 08.03.2020 - 13.03.2020.

The conductance in disordered quantum wires fluctuates with an universal value
of the order of e 2 /h, regardless of the size of the sample and the degree of disor-
der. Graphene samples show an unexpected increase of conductance fluctuations
explained by the additional presence of valley symmetry.
We simulate conductance and shot noise fluctuations in graphene at energies away
from the Dirac point. In a strongly disordered sample with broken valley symmetry
we recover the universal value of a disordered wire. The conductance fluctuations
increase when short-range scatterers are removed and only the long-range part of
the potential is kept, highlighting their sensitivity to valley symmetry. Conductance
fluctuations as a function of energy show a broad plateau at the predicted value. The
level spacing statistics of both systems show the Gaussian-orthogonal universality
class. In the presence of a magnetic field, the systems transitions into the Gaussian-
unitary universality class and the conductance fluctuations decrease. We find a
similar behavior for shot noise fluctuations, suggesting valley symmetry dependence
of universal values also in this case.