1,504 research outputs found
Electrically Tunable Quantum Spin Hall State in Topological Crystalline Insulator Thin films
Based on a combination of theory, band topology analysis and
electronic structure calculations, we predict the (111) thin films of the SnTe
class of three-dimensional (3D) topological crystalline insulators realize the
quantum spin Hall phase in a wide range of thickness. The nontrivial topology
originates from the inter-surface coupling of the topological surface states of
TCI in the 3D limit. The inter-surface coupling changes sign and gives rise to
topological phase transitions as a function of film thickness. Furthermore,
this coupling can be strongly affected by an external electric field, hence the
quantum spin Hall phase can be effectively tuned under experimentally
accessible the electric field. Our results show that (111) thin films of
SnTe-class TCI can be an ideal platform to realize the novel applications of
quantum spin Hall insulators.Comment: Minor revision with updated reference
Post-Regularization Inference for Time-Varying Nonparanormal Graphical Models
We propose a novel class of time-varying nonparanormal graphical models,
which allows us to model high dimensional heavy-tailed systems and the
evolution of their latent network structures. Under this model, we develop
statistical tests for presence of edges both locally at a fixed index value and
globally over a range of values. The tests are developed for a high-dimensional
regime, are robust to model selection mistakes and do not require commonly
assumed minimum signal strength. The testing procedures are based on a high
dimensional, debiasing-free moment estimator, which uses a novel kernel
smoothed Kendall's tau correlation matrix as an input statistic. The estimator
consistently estimates the latent inverse Pearson correlation matrix uniformly
in both the index variable and kernel bandwidth. Its rate of convergence is
shown to be minimax optimal. Our method is supported by thorough numerical
simulations and an application to a neural imaging data set
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