scholarly journals Quantum Pumping with Adiabatically Modulated Barriers in Three-Band Pseudospin-1 Dirac–Weyl Systems

Entropy ◽  
2019 ◽  
Vol 21 (2) ◽  
pp. 209 ◽  
Author(s):  
Xiaomei Chen ◽  
Rui Zhu
Keyword(s):  
Dirac Point ◽  
Berry Phase ◽  
Scattering Matrix ◽  
Flat Band ◽  
Current Direction ◽  
Double Barrier ◽  
Band Dispersion ◽  
Direction Reversal ◽  
Double Barrier Structure ◽  
Weyl Fermions

In this work, pumped currents of the adiabatically-driven double-barrier structure based on the pseudospin-1 Dirac–Weyl fermions are studied. As a result of the three-band dispersion and hence the unique properties of pseudospin-1 Dirac–Weyl quasiparticles, sharp current-direction reversal is found at certain parameter settings especially at the Dirac point of the band structure, where apexes of the two cones touch at the flat band. Such a behavior can be interpreted consistently by the Berry phase of the scattering matrix and the classical turnstile mechanism.

scholarly journals Dirac Dispersion in Two-Dimensional Photonic Crystals

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
C. T. Chan ◽  
Zhi Hong Hang ◽  
Xueqin Huang
Keyword(s):  
Refractive Index ◽  
Photonic Crystals ◽  
Berry Phase ◽  
Flat Band ◽  
Two Dimensional ◽  
Zone Boundary ◽  
System Parameters ◽  
Band Dispersion ◽  
Permittivity And Permeability ◽  
Band Crossing

We show how one may obtain conical (Dirac) dispersions in photonic crystals, and in some cases, such conical dispersions can be used to create a metamaterial with an effective zero refractive index. We show specifically that in two-dimensional photonic crystals with C4v symmetry, we can adjust the system parameters to obtain accidental triple degeneracy at Γ point, whose band dispersion comprises two linear bands that generate conical dispersion surfaces and an additional flat band crossing the Dirac-like point. If this triply degenerate state is formed by monopole and dipole excitations, the system can be mapped to an effective medium with permittivity and permeability equal to zero simultaneously, and this system can transport wave as if the refractive index is effectively zero. However, not all the triply degenerate states can be described by monopole and dipole excitations and in those cases, the conical dispersion may not be related to an effective zero refractive index. Using multiple scattering theory, we calculate the Berry phase of the eigenmodes in the Dirac-like cone to be equal to zero for modes in the Dirac-like cone at the zone center, in contrast with the Berry phase of π for Dirac cones at the zone boundary.

scholarly journals Emergent flat band electronic structure in a VSe2/Bi2Se3 heterostructure

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Turgut Yilmaz ◽  
Xiao Tong ◽  
Zhongwei Dai ◽  
Jerzy T. Sadowski ◽  
Eike F. Schwier ◽  
...  
Keyword(s):  
Dirac Point ◽  
Electronic States ◽  
Quantum States ◽  
Photoemission Spectroscopy ◽  
Flat Band ◽  
Strongly Correlated ◽  
Dirac Cone ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Topological Materials ◽  
Photoemission Study

AbstractFlat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However, materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission spectroscopy, we show the emergent flat band in a VSe2 / Bi2Se3 heterostructure. Our photoemission study demonstrates that the flat band covers the entire Brillouin zone and exhibits 2D nature with a complex circular dichroism. In addition, the Dirac cone of Bi2Se3 is not reshaped by the flat band even though they overlap in proximity of the Dirac point. These features make this flat band distinguishable from the ones previously found. Thereby, the observation of a flat band in the VSe2 / Bi2Se3 heterostructure opens a promising pathway to realize strongly correlated quantum effects in topological materials.

scholarly journals Extremely flat band in bilayer graphene

2018 ◽  
Vol 4 (11) ◽  
pp. eaau0059 ◽  
Author(s):  
D. Marchenko ◽  
D. V. Evtushinsky ◽  
E. Golias ◽  
A. Varykhalov ◽  
Th. Seyller ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Bilayer Graphene ◽  
Flat Band ◽  
Honeycomb Lattice ◽  
Band Model ◽  
Two Dimensional ◽  
Band Formation ◽  
Constant Energy ◽  
Mexican Hat ◽  
Band Dispersion

We propose a novel mechanism of flat band formation based on the relative biasing of only one sublattice against other sublattices in a honeycomb lattice bilayer. The mechanism allows modification of the band dispersion from parabolic to “Mexican hat”–like through the formation of a flattened band. The mechanism is well applicable for bilayer graphene—both doped and undoped. By angle-resolved photoemission from bilayer graphene on SiC, we demonstrate the possibility of realizing this extremely flattened band (< 2-meV dispersion), which extends two-dimensionally in a k-space area around the K¯ point and results in a disk-like constant energy cut. We argue that our two-dimensional flat band model and the experimental results have the potential to contribute to achieving superconductivity of graphene- or graphite-based systems at elevated temperatures.

Short-wave infrared detector with double barrier structure and low dark current density

2016 ◽  
Vol 14 (2) ◽  
pp. 022501-22505
Author(s):  
Yu Dong Yu Dong ◽  
Guanglong Wang Guanglong Wang ◽  
Haiqiao Ni Haiqiao Ni ◽  
Kangming Pei Kangming Pei ◽  
Zhongtao Qiao Zhongtao Qiao ◽  
...  
Keyword(s):  
Current Density ◽  
Dark Current ◽  
Infrared Detector ◽  
Short Wave ◽  
Barrier Structure ◽  
Dark Current Density ◽  
Double Barrier ◽  
Short Wave Infrared ◽  
Double Barrier Structure

THE WIDTH RATIO OF TWO BARRIERS IN RESONANT TUNNELING

2003 ◽  
Vol 17 (03) ◽  
pp. 105-109 ◽  
Author(s):  
MASATO OHMUKAI
Keyword(s):  
Transmission Coefficient ◽  
Resonant Tunneling ◽  
Width Ratio ◽  
Total Width ◽  
Barrier Width ◽  
Barrier Structure ◽  
Double Barrier ◽  
Two Parameters ◽  
Double Barrier Structure ◽  
Two Barriers

Numerical calculations by a transfer matrix method have been performed to obtain the transmission coefficient of rectangular double barrier structures. The dependence of the well width, barrier width and the barrier height was systematically investigated. When the width ratio of the two barriers was varied on condition that a total width was fixed, the transmission coefficient at a resonance is varied while that at a valley region is not. It is concluded that the resonant tunneling is characterized by two parameters: total width and the width ratio. Our results clarify the transition of transmission spectrum from a single barrier to a double barrier structure.

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