Fermi Velocity Reduction of Dirac Fermions around the Brillouin Zone Center in In 2 Se 3 –Bilayer Graphene Heterostructures

2021 ◽  
pp. 2007503
Author(s):  
Zhenyu Wang ◽  
Zhanyang Hao ◽  
Yayun Yu ◽  
Yuan Wang ◽  
Shiv Kumar ◽  
...  
Keyword(s):  
Brillouin Zone ◽  
Bilayer Graphene ◽  
Fermi Velocity ◽  
Dirac Fermions ◽  
Velocity Reduction ◽  
Brillouin Zone Center

Infrared dielectric functions and Brillouin zone center phonons of α−Ga2O3 compared to α - Al2O3

2022 ◽  
Vol 6 (1) ◽  
Author(s):  
Megan Stokey ◽  
Rafał Korlacki ◽  
Matthew Hilfiker ◽  
Sean Knight ◽  
Steffen Richter ◽  
...  
Keyword(s):  
Brillouin Zone ◽  
Α Al2o3 ◽  
Brillouin Zone Center

scholarly journals Dodecagonal bilayer graphene quasicrystal and its approximants

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Guodong Yu ◽  
Zewen Wu ◽  
Zhen Zhan ◽  
Mikhail I. Katsnelson ◽  
Shengjun Yuan
Keyword(s):  
Large Scale ◽  
Lattice Mismatch ◽  
Tight Binding ◽  
Bilayer Graphene ◽  
Dominant Factor ◽  
Honeycomb Lattice ◽  
Fermi Velocity ◽  
Band Theory ◽  
Incommensurate Structures ◽  
Unfolding Method

AbstractDodecagonal bilayer graphene quasicrystal has 12-fold rotational order but lacks translational symmetry which prevents the application of band theory. In this paper, we study the electronic and optical properties of graphene quasicrystal with large-scale tight-binding calculations involving more than ten million atoms. We propose a series of periodic approximants which reproduce accurately the properties of quasicrystal within a finite unit cell. By utilizing the band-unfolding method on the smallest approximant with only 2702 atoms, the effective band structure of graphene quasicrystal is derived. The features, such as the emergence of new Dirac points (especially the mirrored ones), the band gap at $$M$$M point and the Fermi velocity are all in agreement with recent experiments. The properties of quasicrystal states are identified in the Landau level spectrum and optical excitations. Importantly, our results show that the lattice mismatch is the dominant factor determining the accuracy of layered approximants. The proposed approximants can be used directly for other layered materials in honeycomb lattice, and the design principles can be applied for any quasi-periodic incommensurate structures.

scholarly journals Brillouin zone center phonon modes in ZnGa2O4

2020 ◽  
Vol 117 (5) ◽  
pp. 052104 ◽  
Author(s):  
Megan Stokey ◽  
Rafał Korlacki ◽  
Sean Knight ◽  
Matthew Hilfiker ◽  
Zbigniew Galazka ◽  
...  
Keyword(s):  
Brillouin Zone ◽  
Phonon Modes ◽  
Brillouin Zone Center

scholarly journals Moire Is Different

2021 ◽  
Vol 13 (1) ◽  
pp. 50
Author(s):  
Wenyuan Shi
Keyword(s):  
Electronic Structures ◽  
Tight Binding ◽  
Physical Property ◽  
Large Change ◽  
Bilayer Graphene ◽  
Dirac Fermion ◽  
Dirac Fermions ◽  
Graphene Layers ◽  
Flat Bands ◽  
Twisted Bilayer Graphene

Graphene, as the thinnest material ever found, exhibits unconventionally relativistic behaviour of Dirac fermions. However, unusual phenomena (such as superconductivity) arise when stacking two graphene layers and twisting the bilayer graphene. The relativistic Dirac fermion in graphene has been widely studied and understood, but the large change observed in twisted bilayer graphene (TBG) is intriguing and still unclear because only van der Waals force (vdW) interlayer interaction is added from graphene to TBG and such a very weak interaction is expected to play a negligible role. To understand such dramatic variation, we studied the electronic structures of monolayer, bilayer and twisted bilayer graphene. Twisted bilayer graphene creates different moiré patterns when turned at different angles. We proposed tight-binding and effective continuum models and thereby drafted a computer code to calculate their electronic structures. Our calculated results show that the electronic structure of twisted bilayer graphene changes significantly even by a tiny twist. When bilayer graphene is twisted at special “magic angles”, flat bands appear. We examined how these flat bands are created, their properties and the relevance to some unconventional physical property such as superconductivity. We conclude that in the nanoscopic scale, similar looking atomic structures can create vastly different electronic structures. Like how P. W. Anderson stated that similar looking fields in science can have differences in his article “More is Different”, similar moiré patterns in twisted bilayer graphene can produce different electronic structures.

scholarly journals Coexistence of electron whispering-gallery modes and atomic collapse states in graphene/WSe2 heterostructure quantum dots

2021 ◽  
Author(s):  
Qi Zheng ◽  
Yu-Chen Zhuang ◽  
Qingfeng Sun ◽  
Lin He
Keyword(s):  
Quantum Dots ◽  
Graphene Quantum Dots ◽  
Whispering Gallery Modes ◽  
Fermi Velocity ◽  
Dirac Fermions ◽  
Heavy Nuclei ◽  
Whispering Gallery ◽  
Klein Tunneling ◽  
Collapse State ◽  
A Charge

Abstract The relativistic massless charge carriers with a Fermi velocity of about c/300 in graphene enable us to realize two distinct types of resonances (c, the speed of light in vacuum). One is electron whispering-gallery mode in graphene quantum dots arising from the Klein tunneling of the massless Dirac fermions. The other is atomic collapse state, which has never been observed in experiment with real atoms due to the difficulty of producing heavy nuclei with charge Z > 170, however, can be realized near a Coulomb impurity in graphene with a charge Z ≥ 1 because of the “small” velocity of the Dirac excitations. Here, unexpectedly, we demonstrate that both the electron whispering-gallery modes and atomic collapse states coexist in graphene/WSe2 heterostructure quantum dots due to the Coulomb-like potential near their edges. By applying a perpendicular magnetic field, evolution from the atomic collapse states to unusual Landau levels in the collapse regime are explored for the first time.

Observation of a Thermodynamic Distinction Between Brillouin Zone Center and Boundary Exciton States in MnF2

1968 ◽  
Vol 21 (15) ◽  
pp. 1067-1070 ◽  
Author(s):  
R. E. Dietz ◽  
A. E. Meixner ◽  
H. J. Guggenheim ◽  
A. Misetich
Keyword(s):  
Brillouin Zone ◽  
Brillouin Zone Center

scholarly journals Ultrafast Dynamics of Massive Dirac Fermions in Bilayer Graphene

2014 ◽  
Vol 112 (25) ◽  
Author(s):  
Søren Ulstrup ◽  
Jens Christian Johannsen ◽  
Federico Cilento ◽  
Jill A. Miwa ◽  
Alberto Crepaldi ◽  
...  
Keyword(s):  
Bilayer Graphene ◽  
Ultrafast Dynamics ◽  
Dirac Fermions
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