220 research outputs found
Bulk effects on topological conduction on the surface of 3-D topological insulators
The surface states of a topological insulator in a fine-tuned magnetic field
are ideal candidates for realizing a topological metal which is protected
against disorder. Its signatures are (1) a conductance plateau in long wires in
a finely tuned longitudinal magnetic field and (2) a conductivity which always
increases with sample size, and both are independent of disorder strength. We
numerically study how these experimental transport signatures are affected by
bulk physics in the interior of the topological insulator sample. We show that
both signatures of the topological metal are robust against bulk effects.
However the bulk does substantially accelerate the metal's decay in a magnetic
field and alter its response to surface disorder. When the disorder strength is
tuned to resonance with the bulk band the conductivity follows the predictions
of scaling theory, indicating that conduction is diffusive. At other disorder
strengths the bulk reduces the effects of surface disorder and scaling theory
is systematically violated, signaling that conduction is not fully diffusive.
These effects will change the magnitude of the surface conductivity and the
magnetoconductivity
Artificial Neural Network Approach to the Analytic Continuation Problem
Inverse problems are encountered in many domains of physics, with analytic
continuation of the imaginary Green's function into the real frequency domain
being a particularly important example. However, the analytic continuation
problem is ill defined and currently no analytic transformation for solving it
is known. We present a general framework for building an artificial neural
network (ANN) that solves this task with a supervised learning approach.
Application of the ANN approach to quantum Monte Carlo calculations and
simulated Green's function data demonstrates its high accuracy. By comparing
with the commonly used maximum entropy approach, we show that our method can
reach the same level of accuracy for low-noise input data, while performing
significantly better when the noise strength increases. The computational cost
of the proposed neural network approach is reduced by almost three orders of
magnitude compared to the maximum entropy methodComment: 6 pages, 4 figures, supplementary material available as ancillary
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