177 research outputs found
Higher-order Topology of Axion Insulator EuInAs
Based on first-principles calculations and symmetry analysis, we propose that
EuInAs is a long awaited axion insulator with antiferromagnetic (AFM)
long range order. Characterized by the parity-based invariant ,
the topological magneto-electric effect is quantized with in the
bulk, with a band gap as large as 0.1 eV. When the staggered magnetic moment of
the AFM phase is along axis, it's also a TCI phase. Gapless surface
states emerge on (100), (010) and (001) surfaces, protected by mirror
symmetries (nonzero mirror Chern numbers). When the magnetic moment is along
axis, the (100) and (001) surfaces are gapped. As a consequence of a
high-order topological insulator with , the one-dimensional (1D)
chiral state can exist on the hinge between those gapped surfaces. We have
calculated both the topological surface states and hinge state in different
phases of the system, respectively, which can be detected by ARPES or STM
experiments
The Reduced Order Method for Solving the Linear Complementarity Problem with an M-Matrix
In this paper, by seeking the zero and the positive entry positions of the solution, we provide a direct method, called the reduced order method, for solving the linear complementarity problem with an M-matrix. By this method, the linear complementarity problem is transformed into a low order linear complementarity problem with some low order linear equations and the solution is constructed by the solution of the low order linear complementarity problem and the solutions of these low order linear equations in the transformations. In order to show the accuracy and the effectiveness of the method, the corresponding numerical experiments are performed
Strong and fragile topological Dirac semimetals with higher-order Fermi arcs
Dirac and Weyl semimetals both exhibit arc-like surface states. However, whereas the surface Fermi arcs in Weyl semimetals are topological consequences of the Weyl points themselves, the surface Fermi arcs in Dirac semimetals are not directly related to the bulk Dirac points, raising the question of whether there exists a topological bulk-boundary correspondence for Dirac semimetals. In this work, we discover that strong and fragile topological Dirac semimetals exhibit one-dimensional (1D) higher-order hinge Fermi arcs (HOFAs) as universal, direct consequences of their bulk 3D Dirac points. To predict HOFAs coexisting with topological surface states in solid-state Dirac semimetals, we introduce and layer a spinful model of an s–d-hybridized quadrupole insulator (QI). We develop a rigorous nested Jackiw–Rebbi formulation of QIs and HOFA states. Employing ab initio calculations, we demonstrate HOFAs in both the room- (α) and intermediate-temperature (α″) phases of Cd3As2, KMgBi, and rutile-structure (β′-) PtO2
MoTe2: A Type-II Weyl Topological Metal
Based on the ab initio calculations, we show that MoTe2, in its
low-temperature orthorhombic structure characterized by an X-ray diffraction
study at 100 K, realizes 4 type-II Weyl points between the N-th and N+1-th
bands, where N is the total number of valence electrons per unit cell. Other
WPs and nodal lines between different other bands also appear close to the
Fermi level due to a complex topological band structure. We predict a series of
strain-driven topological phase transitions in this compound, opening a wide
range of possible experimental realizations of different topological semimetal
phases. Crucially, with no strain, the number of observable surface Fermi arcs
in this material is 2 - the smallest number of arcs consistent with
time-reversal symmetry.Comment: Published versio
Tandem-pumped, tunable thulium-doped fiber laser in 21 μm wavelength region
We present a continuously tunable thulium(Tm)-doped fiber laser operating in the important 2.1 μm region, which is tandem-pumped by another Tm-doped fiber laser at 1908 nm. The advantages of pumping a Tm-doped fiber laser at the long-wavelength absorption tail (>1900 nm) of the fiber include a reduced quantum-defect, and efficient suppression of the amplified spontaneous noise (and potential parasitic lasing) at the short-wavelength region. This facilitates attainment of stable lasing operation in the long-wave emission tail of the Tm fiber at ~2.1 μm. By rotating a diffraction grating inside the Tm fiber laser cavity, we experimentally achieved a wavelength-tuning range of 2000-2172 nm. At central wavelengths of 2050 nm, 2150 nm, and 2172 nm, the slope efficiencies were 23%, 16%, and 9.9%, respectively. To the best of our knowledge, this is the first demonstration of long-wavelength operation of a Tm fiber laser system tandem-pumped at >1900 nm
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