2 research outputs found
Impact of clustering of substitutional impurities on quasiparticle lifetimes and localization
Motivated by the observation and prediction of clustering behavior for
impurities substituted into the host lattice of a real material, and the
dramatic impact this can have on electronic properties, we develop a simple
approach to describe such an effect via the electron self-energy. We employ a
disorder averaged T-matrix expansion taken to second order, which we modify to
include a clustering probability parameter. This approach circumvents the need
for specific cluster probability distributions, simplifying greatly the
analysis of clustered impurities. To gain analytical insights, we study a
nearest-neighbor square lattice tight-binding Hamiltonian with clustered
impurity substitutions to investigate clustering of off-diagonal hopping
impurities. We find that our T-matrix approach is in excellent agreement with
exact numerical results from a tight-binding computation performed with the
KWANT package. We observe a variety of interesting impurity clustering-induced
effects in the self-energy such as the suppression of quasi-particle lifetimes
at certain momenta and an increase in localization, as indicated by the inverse
participation ratio. The KWANT results are reproduced in our modified T-matrix
approach. In addition, our method allows for a full analytical treatment of
clustering effects which can aid in physical insight.Comment: 8 pages, 6 figure
Deep learning of deformation-dependent conductance in thin films: nanobubbles in graphene
Motivated by the ever-improving performance of deep learning techniques, we
design a mixed input convolutional neural network approach to predict transport
properties in deformed nanoscale materials using a height map of deformations
(from scanning probe information) as input. We employ our approach to study
electrical transport in a graphene nanoribbon deformed by a number of randomly
positioned nano-bubbles. Our network is able to make conductance predictions
valid to an average error of 4.3\%. We demonstrate that such low average errors
are achieved by including additional inputs like energy in a highly redundant
fashion, which allows predictions that are 30-40\% more accurate than
conventional architectures. We demonstrate that the same method can learn to
predict the valley-resolved conductance, with success specifically in
identifying the energy at which inter-valley scattering becomes prominent. We
demonstrate the robustness of the approach by testing the pre-trained network
on samples with deformations differing in number and shape from the training
data. We employ a graph theoretical analysis of the structure and outputs of
the network and conclude that a tight-binding Hamiltonian is effectively
encoded in the first layer of the network. We confirm our graph theoretical
analysis numerically for different hopping processes in a trained network and
find the result to be accurate within an error of 1\%. Our approach contributes
a new theoretical understanding and a refined methodology to the application of
deep learning for the determination transport properties based on real-space
disorder information.Comment: 15 pages, 12 figure