1,176 research outputs found
Negative-Index Refraction in a Lamellar Composite with Alternating Single Negative Layers
Negative-index refraction is achieved in a lamellar composite with
epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively.
Based on the effective medium approximation, simultaneously negative effective
permittivity and permeability of such a lamellar composite are obtained
theoretically and further proven by full-wave simulations. Consequently, the
famous left-handed metamaterial comprising split ring resonators and wires is
interpreted as an analogy of such an ENG-MNG lamellar composite. In addition,
beyond the effective medium approximation, the propagating field squeezed near
the ENG/MNG interface is demonstrated to be left-handed surface waves with
backward phase velocity.Comment: 18 pages, 6 figure
Robustness of Half-Integer Quantized Hall Conductivity against Disorder in an Anisotropic Dirac Semimetal with Parity Anomaly
Two-dimensional Dirac semimetals with a single massless Dirac cone exhibit
the parity anomaly. Usually, such a kind of anomalous topological semimetallic
phase in real materials is unstable where any amount of disorder can drive it
into a diffusive metal and destroy the half-integer quantized Hall conductivity
as an indicator of parity anomaly. Here, based on low-energy effective model,
we propose an anisotropic Dirac semimetal which explicitly breaks time-reversal
symmetry and carries a half-integer quantized Hall conductivity. This
topological semimetallic phase can be realized on a deformed honeycomb lattice
subjected to a magnetic flux. Moreover, we perceptively investigate the
disorder correction to the Hall conductivity. The results show that the effects
of disorder can be strongly suppressed and thereby the nearly half-integer
quantization of Hall conductivity can exist in a wide region of disorder,
indicating that our proposed anisotropic Dirac semimetal is an exciting
platform to investigate the parity anomaly phenomena.Comment: 7 pages, 4 figure
The One-dimensional Chiral Anomaly and its Disorder Response
The condensed-matter realization of chiral anomaly has attracted tremendous
interest in exploring unexpected phenomena of quantum field theory. Here, we
show that one-dimensional (1D) chiral anomaly (i.e., 1D nonconservational
chiral current under a background electromagnetic field) can be realized in a
generalized Su-Schrieffer-Heeger model where a single gapless Dirac cone
occurs. Based on the topological Thouless pump and anomalous dynamics of chiral
displacement, we elucidate that such a system possesses the half-integer
quantization of winding number. Moreover, we investigate the evolution of 1D
chiral anomaly with respect to two typical types of disorder, i.e., on-site
disorder and bond disorder. The results show that the on-site disorder tends to
smear the gapless Dirac cone. However, we propose a strategy to stabilize the
half-integer quantization, facilitating its experimental detection.
Furthermore, we demonstrate that the bond disorder causes a unique crossover
with disorder-enhanced topological charge pumping, driving the system into a
topological Anderson insulator phase
Photoinduced High-Chern-Number Quantum Anomalous Hall Effect from Higher-Order Topological Insulators
Quantum anomalous Hall (QAH) insulators with high Chern number host multiple
dissipationless chiral edge channels, which are of fundamental interest and
promising for applications in spintronics and quantum computing. However, only
a limited number of high-Chern-number QAH insulators have been reported to
date. Here, we propose a dynamic approach for achieving high-Chern-number QAH
phases in periodically driven two-dimensional higher-order topological
insulators (HOTIs).In particular, we consider two representative kinds of HOTIs
which are characterized by a quantized quadruple moment and the second
Stiefel-Whitney number, respectively. Using the Floquet formalism for
periodically driven systems, we demonstrate that QAH insulators with tunable
Chern number up to four can be achieved. Moreover, we show by first-principles
calculations that the monolayer graphdiyne, a realistic HOTI, is an ideal
material candidate. Our work not only establishes a strategy for designing
high-Chern-number QAH insulators in periodically driven HOTIs, but also
provides a powerful approach to investigate exotic topological states in
nonequilibrium cases.Comment: 6 pages, 3 figure
Conservation of connectivity of model-space effective interactions under a class of similarity transformation
Effective interaction operators usually act on a restricted model space and
give the same energies (for Hamiltonian) and matrix elements (for transition
operators etc.) as those of the original operators between the corresponding
true eigenstates. Various types of effective operators are possible. Those well
defined effective operators have been shown being related to each other by
similarity transformation. Some of the effective operators have been shown to
have connected-diagram expansions. It is shown in this paper that under a class
of very general similarity transformations, the connectivity is conserved. The
similarity transformation between hermitian and non-hermitian
Rayleigh-Schr\"{o}dinger perturbative effective operators is one of such
transformation and hence the connectivity can be deducted from each other.Comment: 12 preprint page
Nanoporous Zeolite Thin Film-Based Fiber Intrinsic Fabry-Perot Interferometric Sensor for Detection of Dissolved Organics in Water
A fiber optic intrinsic Fabry-Perot interferometric (IFPI) chemical sensor was developed by fine-polishing a thin layer of polycrystalline nanoporous MFI zeolite synthesized on the cleaved endface of a single mode fiber. The sensor operated by monitoring the optical thickness changes of the zeolite thin film caused by the adsorption of organic molecules into the zeolite channels. The optical thickness of the zeolite thin film was measured by white light interferometry. Using methanol, 2-propanol, and toluene as the model chemicals, it was demonstrated that the zeolite IPFI sensor could detect dissolved organics in water with high sensitivity
Clinical comparison between a percutaneous hydraulic pressure delivery system and balloon tamp system using high-viscosity cement for the treatment of osteoporotic vertebral compression fractures
OBJECTIVES: Osteoporotic vertebral compression fractures (OVCFs) affect the elderly population, especially postmenopausal women. Percutaneous kyphoplasty is designed to treat painful vertebral compression fractures for which conservative therapy has been unsuccessful. High-viscosity cement can be injected by either a hydraulic pressure delivery system (HPDS) or a balloon tamp system (BTS). Therefore, the purpose of this study was to compare the safety and clinical outcomes of these two systems. METHODS: A random, multicenter, prospective study was performed. Clinical and radiological assessments were carried out, including assessments of general surgery information, visual analog scale, quality of life, cement leakage, and height and angle restoration. RESULTS: Using either the HPDS or BTS to inject high-viscosity cement effectively relieved pain and improved the patients’ quality of life immediately, and these effects lasted at least two years. The HPDS using high-viscosity cement reduced cost, surgery time, and radiation exposure and showed similar clinical results to those of the BTS. In addition, the leakage rate and the incidence of adjacent vertebral fractures after the HPDS treatment were reduced compared with those after treatment using the classic vertebroplasty devices. However, the BTS had better height and angle restoration abilities. CONCLUSIONS: The percutaneous HPDS with high-viscosity cement has similar clinical outcomes to those of traditional procedures in the treatment of vertebral fractures in the elderly. The HPDS with high-viscosity cement is better than the BTS in the treatment of mild and moderate OVCFs and could be an alternative method for the treatment of severe OVCFs
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