68 research outputs found
A Dirac-fermion approach and its application to design high Chern numbers in magnetic topological insulator multilayers
Quantum anomalous Hall (QAH) insulators host topologically protected
dissipationless chiral edge states, the number of which is determined by its
Chern number. Up to now, the QAH state has been realized in a few magnetic
topological insulators, but usually with a low Chern number. Here, we develop a
Dirac-fermion approach which is valuable to understand and design high Chern
numbers in various multilayers of layered magnetic topological insulators.
Based on the Dirac-fermion approach, we demonstrate how to understand and tune
high Chern numbers in ferromagentic MnBiTe films through the van
der Waals (vdW) gap modulation. Further, we also employ the Dirac-fermion
approach to understand the experimentally observed high Chern numbers and
topological phase transition from the Chern number to in the
[3QL-(Bi,Sb)CrTe]/[4QL-(Bi,Sb)Te]
multilayers. Our work provides a powerful tool to design the QAH states with a
high Chern number in layered magnetic topological insulator multilayers.Comment: 11 pages, 4 figure
Floquet engineering of magnetic topological insulator MnBiTe films
Floquet engineering is an important way to manipulate the electronic states
of condensed matter physics. Recently, the discovery of the magnetic
topological insulator MnBiTe and its family provided a valuable
platform to study magnetic topological phenomena, such as, the quantum
anomalous Hall effect, the axion insulator state and the topological
magnetoelectric effect. In this work, based on the effective model and
first-principles calculations in combination with the Floquet theory, we reveal
that the circularly polarized light (CPL) induces the sign reversal of the
Chern number of odd-septuple-layer (SL) MnBiTe thin films. In contrast,
the CPL drives the axion insulator state into the quantum anomalous Hall state
in even-SL MnBiTe thin films. More interestingly, if the topmost van
der Waals gap between the surface layer and the below bulk in MnBiTe
films is slightly expanded, a high Chern number can be realized under
the CPL. Our work demonstrates that the light can induce rich magnetic
topological phases in MnBiTe films, which might have potential
applications in optoelectronic devices.Comment: 7 pages, 4 figure
Frequency-domain criterion on the stabilizability for infinite-dimensional linear control systems
A quantitative frequency-domain condition related to the exponential
stabilizability for infinite-dimensional linear control systems is presented.
It is proven that this condition is necessary and sufficient for the
stabilizability of special systems, while it is a necessary condition for the
stabilizability in general. Applications are provided.Comment: 26 Page
Tunable dynamical magnetoelectric effect in antiferromagnetic topological insulator MnBiTe films
More than forty years ago, axion was postulated as an elementary particle
with a low mass and weak interaction in particle physics to solve the strong
(charge conjugation and parity) puzzle. Axions are also
considered as a possible component of dark matter of the universe. However, the
existence of axions in nature has not been confirmed. Interestingly, axions
arise as pseudoscalar fields derived from the Chern-Simons theory in condensed
matter physics. In antiferromagnetic insulators, the axion field can become
dynamical induced by spin-wave excitations and exhibits rich exotic phenomena,
such as, the chiral magnetic effect, axionic polariton and so on. However, the
study of the dynamical axion field is rare due to the lack of real materials.
Recently, MnBiTe was discovered to be an antiferromagnetic topological
insulator with a quantized axion field protected by the inversion symmetry
and the magnetic-crystalline symmetry . Here, we
studied MnBiTe films in which both the and
symmetries are spontaneously broken and found that the dynamical axion field
and largely tunable dynamical magnetoelectric effects can be realized through
tuning the thickness of MnBiTe films, the temperature and the element
substitution. Our results open a broad avenue to study axion dynamics in
antiferromagnetic topological insulator MnBiTe and related materials,
and also is hopeful to promote the research of dark matter.Comment: 6 pages, 4 figure
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