scholarly journals Two-dimensional Stiefel-Whitney insulators in liganded Xenes

2022 ◽  
Vol 8 (1) ◽  
Author(s):  
Mingxiang Pan ◽  
Dexin Li ◽  
Jiahao Fan ◽  
Huaqing Huang
Keyword(s):  
Group Iv ◽  
Two Dimensional ◽  
Experimental Characterization ◽  
Berry Curvature ◽  
Tunable Bandgap ◽  
Topological State ◽  
Whitney Class ◽  
Fundamental Research ◽  
Nontrivial Topology

AbstractTwo-dimensional (2D) Stiefel-Whitney insulator (SWI), which is characterized by the second Stiefel-Whitney class, is a class of topological phases with zero Berry curvature. As an intriguing topological state, it has been well studied in theory but seldom realized in realistic materials. Here we propose that a large class of liganded Xenes, i.e., hydrogenated and halogenated 2D group-IV honeycomb lattices, are 2D SWIs. The nontrivial topology of liganded Xenes is identified by the bulk topological invariant and the existence of protected corner states. Moreover, the large and tunable bandgap (up to 3.5 eV) of liganded Xenes will facilitate the experimental characterization of the 2D SWI phase. Our findings not only provide abundant realistic material candidates that are experimentally feasible but also draw more fundamental research interest towards the topological physics associated with Stiefel-Whitney class in the absence of Berry curvature.

Experimental characterization of steady two-dimensional vortex couples

1988 ◽  
Vol 192 ◽  
pp. 175-192 ◽  
Author(s):  
Jean-Michel Nguyen Duc ◽  
Joël Sommeria
Keyword(s):  
Electric Pulse ◽  
Steady Motion ◽  
Horizontal Layer ◽  
Two Dimensional ◽  
Experimental Characterization ◽  
Small Particles ◽  
General Stability ◽  
Flow Circulation ◽  
External Frame

We study the evolution of unsteady two-dimensional vorticity structures surrounded by fluid at rest. The flow is initiated by a short fluid impulse in a horizontal layer of mercury and is constrained to be two-dimensional by a vertical uniform magnetic field. The impulse is generated by an electric pulse between two electrodes, and a flow circulation can be produced by diverting part of the current through the external frame. The velocity field is measured from the streaks of small particles floating on the free upper surface, and the vorticity is then obtained by means of an analytical interpolation and differentiation. The flow always evolves toward a set of independent steady structures with symmetry which are either circular vortices (monopoles) or couples (dipoles). The latter have a linear or circular steady motion depending on the flow circulation around them. The region of non-zero vorticity is always close to a circle. The steadiness is confirmed by plotting the vorticity versus the stream function in the frame of reference moving with the couple. We obtain a curve, as appropriate for a steady solution of the Euler equation. The slope of this curve is either constant or has no maximum. We suggest that this result could correspond to a general stability condition. The interaction between two symmetric couples at various angles of incidence yields two new couples by exchange of their vortices. Oscillations of the resulting couples are often damped by releasing a circular vortex.

Experimental Characterization of E-Band Two-Dimensional Electronically Beam-Steerable Integrated Lens Antennas

2013 ◽  
Vol 12 ◽  
pp. 1188-1191 ◽  
Author(s):  
Alexey Artemenko ◽  
Andrey Mozharovskiy ◽  
Alexander Maltsev ◽  
Roman Maslennikov ◽  
Alexey Sevastyanov ◽  
...  
Keyword(s):  
Two Dimensional ◽  
Experimental Characterization ◽  
Lens Antennas

Experimental characterization of viscoelastic effects on two- and three-dimensional shear instabilities

2000 ◽  
Vol 416 ◽  
pp. 151-172 ◽  
Author(s):  
OLIVIER CADOT ◽  
SATISH KUMAR
Keyword(s):  
Turbulent Flows ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Experimental Characterization ◽  
Elastic Forces ◽  
Viscoelastic Effects ◽  
Karman Street ◽  
Dimensional Instability ◽  
Elasticity Number

Instabilities of a wake produced by a circular cylinder in a uniform water flow are studied experimentally when viscoelastic solutions are injected through holes pierced in the cylinder. It is shown that the viscoelastic solutions fill the shear regions and drastically modify the instabilities. The two-dimensional instability giving rise to the Kármán street is found to be inhibited: the roll-up process appears to be delayed and the wavelength of the street increases. The wavelength increase obeys an exponential law and depends on the elasticity number, which provides a ratio of elastic forces to inertial forces. The three-dimensional instability leading to the A mode is generally found to be suppressed. In the rare case where the A mode is observed, its wavelength is shown to be proportional to the wavelength of the Kármán street and the streamwise stretching appears to be inhibited. Injection of viscoelastic solutions also decreases the aspect ratio of the two-dimensional wake, and this is correlated with stabilization of the A mode and with changes in the shape of the Kármán vortices. The observations of this work are consistent with recent numerical simulations of viscoelastic mixing layers. The results suggest mechanisms through which polymers inhibit the formation of high-vorticity coherent structures and reduce drag in turbulent flows.

Experimental characterization of two‐dimensional dopant profiles in silicon using chemical staining

1988 ◽  
Vol 52 (25) ◽  
pp. 2145-2147 ◽  
Author(s):  
Ravi Subrahmanyan ◽  
Hisham Z. Massoud ◽  
Richard B. Fair
Keyword(s):  
Two Dimensional ◽  
Experimental Characterization ◽  
Dopant Profiles
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