7,134 research outputs found
Pole expansion of self-energy and interaction effect on topological insulators
We study effect of interactions on time-reversal-invariant topological
insulators. Their topological indices are expressed by interacting Green's
functions. Under the local self-energy approximation, we connect topological
index and surface states of an interacting system to an auxiliary
noninteracting system, whose Hamiltonian is related to the pole-expansions of
the local self-energy. This finding greatly simplifies the calculation of
interacting topological indices and gives an noninteracting pictorial
description of interaction driven topological phase transitions. Our results
also bridge studies of the correlated topological insulating materials with the
practical dynamical-mean-field-theory calculations.Comment: 4.2 pages, 3 figures, reference added, typos correcte
Floquet Majorana fermions in driven hexagonal lattice systems
We propose Floquet chiral topological superconducting systems hosting Floquet
Majorana fermions, which consist of hexagonal lattices in proximity to
superconductors with shining circularly polarized light. Specially for bilayer
graphene system, we demonstrate that there exist three topological phases
determined by certain parameters, namely, the amplitude and frequency of the
induced light. The number of chiral Floquet Majorana edge states is confirmed
by calculating Chern number analytically and energy spectrum in ribbon
geometry. Moreover, this proposal is generalized to other hexagonal lattice
systems, such as monolayer graphene and silicene. Notably, the parameter range
of induced light to achieve the chiral Floquet Majorana edge states is
experimentally feasible, and the corresponding Floquet Majorana fermions can be
probed based on differential conductance using scanning tunneling spectroscopy.Comment: 9 pages, 8 figure
Building topological device through emerging robust helical surface states
We propose a nonlocal manipulation method to build topological devices
through emerging robust helical surface states in Z_2=0 topological systems.
Specifically, in a ribbon of Z_2=0 Bernevig- Hughes-Zhang (BHZ) model with
finite-size effect, if magnetic impurities are doped on the top (bottom) edge,
the edge states on the bottom (top) edge can be altered according to the
strengths and directions of these magnetic impurities. Consequently, the
backscattering between the emerging robust helical edge states and gapped
normal edge states due to finite-size confinement is also changed, which makes
the system alternate between a perfect one-channel conductor and a perfect
insulator. This effect allows us to fabricate topological devices with high
on-off ratio. Moreover, it can also be generalized to 3D model and more
realistic Cd3As2 type Dirac semimetals.Comment: 7 pages, 6 figure
Power-Partible Reduction and Congruences
Based on the polynomial reduction, a holonomic (or, P-recursive) sequence
can be decomposed into a summable part and a reduced part. In this
paper, we show that when has a certain kind of symmetry, the reduced
part contains only odd or even powers. The reduction in this case is called a
power-partible reduction, which is then applied to obtain new series of
congruences for Ap\'ery numbers and central Delannoy polynomials
. In particular, when is a prime, we prove that for each
r\in\bN, there is a -adic integer such that \begin{equation*}
\sum_{k=0}^{p-1}(2k+1)^{2r+1}A_k\equiv c_r p \pmod {p^3}. \end{equation*
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Bioinspired Multifunctional Anti-icing Hydrogel
The recent anti-icing strategies in the state of the art mainly focused on three aspects: inhibiting ice nucleation, preventing ice propagation, and decreasing ice adhesion strength. However, it is has proved difficult to prevent ice nucleation and propagation while decreasing adhesion simultaneously, due to their highly distinct, even contradictory design principles. In nature, anti-freeze proteins (AFPs) offer a prime example of multifunctional integrated anti-icing materials that excel in all three key aspects of the anti-icing process simultaneously by tuning the structures and dynamics of interfacial water. Here, inspired by biological AFPs, we successfully created a multifunctional anti-icing material based on polydimethylsiloxane-grafted polyelectrolyte hydrogel that can tackle all three aspects of the anti-icing process simultaneously. The simplicity, mechanical durability, and versatility of these smooth hydrogel surfaces make it a promising option for a wide range of anti-icing applications
Spin current through an ESR quantum dot: A real-time study
The spin transport in a strongly interacting spin-pump nano-device is studied
using the time-dependent variational-matrix-product-state (VMPS) approach. The
precession magnetic field generates a dissipationless spin current through the
quantum dot. We compute the real time spin current away from the equilibrium
condition. Both transient and stationary states are reached in the simulation.
The essentially exact results are compared with those from the Hartree-Fock
approximation (HFA). It is found that correlation effect on the physical
quantities at quasi-steady state are captured well by the HFA for small
interaction strength. However the HFA misses many features in the real time
dynamics. Results reported here may shed light on the understanding of the
ultra-fast processes as well as the interplay of the non-equilibrium and
strongly correlated effect in the transport properties.Comment: 5 pages, 5 figure
Disorder and metal-insulator transitions in Weyl semimetals
The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has
Weyl nodes in bulk excitations and Fermi arcs surface states. We study the
effects of disorder and localization in WSMs and find three exotic phase
transitions. (I) Two Weyl nodes near the Brillouin zone boundary can be
annihilated pairwise by disorder scattering, resulting in the opening of a
topologically nontrivial gap and a transition from a WSM to a three-dimensional
(3D) quantum anomalous Hall state. (II) When the two Weyl nodes are well
separated in momentum space, the emergent bulk extended states can give rise to
a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (III)
Two Weyl nodes can emerge near the zone center when an insulating gap closes
with increasing disorder, enabling a direct transition from a normal band
insulator to a WSM. We determine the phase diagram by numerically computing the
localization length and the Hall conductivity, and propose that the exotic
phase transitions can be realized on a photonic lattice.Comment: 7 pages with appendix, 6 figure
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