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.

scholarly journals Interaction effects and superconductivity signatures in twisted double-bilayer WSe2

2020 ◽  
Vol 5 (9) ◽  
pp. 1309-1316 ◽  
Author(s):  
Liheng An ◽  
Xiangbin Cai ◽  
Ding Pei ◽  
Meizhen Huang ◽  
Zefei Wu ◽  
...  
Keyword(s):  
Interaction Effects ◽  
Bilayer Graphene ◽  
Insulator Transition ◽  
Electron Interaction ◽  
Flat Band ◽  
Two Dimensional ◽  
Twisted Bilayer Graphene ◽  
Interaction Phenomena

Twisted bilayer graphene provides a new two-dimensional platform for studying electron interaction phenomena and flat band properties such as correlated insulator transition, superconductivity and ferromagnetism at certain magic angles.

scholarly journals Designing spin-textured flat bands in twisted graphene multilayers via helimagnet encapsulation

2D Materials ◽  
2022 ◽  
Author(s):  
Guangze Chen ◽  
Maryam Khosravian ◽  
Jose Lado ◽  
Aline Ramires
Keyword(s):  
Helical Structure ◽  
Bilayer Graphene ◽  
Flat Band ◽  
Two Dimensional ◽  
Local Exchange ◽  
Flat Bands ◽  
Starting Point ◽  
Twisted Bilayer Graphene ◽  
Spin Texture ◽  
Twisted Graphene

Abstract Twisted graphene multilayers provide tunable platforms to engineer flat bands and exploit the associated strongly correlated physics. The two-dimensional nature of these systems makes them suitable for encapsulation by materials that break specific symmetries. In this context, recently discovered two-dimensional helimagnets, such as the multiferroic monolayer NiI2, are specially appealing for breaking time-reversal and inversion symmetries due to their nontrivial spin textures. Here we show that this spin texture can be imprinted on the electronic structure of twisted bilayer graphene by proximity effect. We discuss the dependence of the imprinted spin texture on the wave-vector of the helical structure, and on the strength of the effective local exchange field. Based on these results we discuss the nature of the superconducting instabilities that can take place in helimagnet encapsulated twisted bilayer graphene. Our results put forward helimagnetic encapsulation as a powerful way of designing spin-textured flat band systems, providing a starting point to engineer a new family of correlated moire states.

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 Realistic flat-band model based on degenerate p-orbitals in two-dimensional ionic materials

2021 ◽  
Author(s):  
Jiang Zeng ◽  
Ming Lu ◽  
Haiwen Liu ◽  
Hua Jiang ◽  
X.C. Xie
Keyword(s):  
Flat Band ◽  
Band Model ◽  
Two Dimensional ◽  
Model Based ◽  
Ionic Materials

scholarly journals TUNABLE CLOAKING OF MEXICAN-HAT CONFINED STATES IN BILAYER SILICENE

2019 ◽  
Vol 29 (3) ◽  
Author(s):  
Lan Tran ◽  
Le Bin Ho
Keyword(s):  
Electric Field ◽  
Quantum Transport ◽  
Incident Energy ◽  
Bilayer Graphene ◽  
Low Energy ◽  
Band Model ◽  
Spin Orbit Coupling ◽  
Mexican Hat ◽  
Transfer Matrix Approach ◽  
Potential Height

We present the ballistic quantum transport of a p-n-p bilayer silicene junction in the presence of spin-orbit coupling and electric field using a four-band model in combination with the transfer-matrix approach. A Mexican-hat shape of low-energy spectrum is observed similarly to bilayer graphene under an interalayer bias. We show that while bilayer silicene shares some physics with bilayer graphene, it has many intriguing phenomena that have not been reported for the latter. First, the confined state producing a significantly non-zero transmission in Mexican hat. Second, the cloaking of the Mexican-hat confined state is found. Third, we observe that the Mexican-hat cloaking results in a strong oscillation of conductance when the incident energy is below the potential height. Finally, unlike monolayer silicene, the conductance at large interlayer distances increases with the rise of electric field when the incident energy is above the potential height. 

scholarly journals Unfolding energy spectra of double-periodicity two-dimensional systems: Twisted bilayer graphene and MoS2 on graphene

2018 ◽  
Vol 2 (1) ◽  
Author(s):  
Yu-ichiro Matsushita ◽  
Hirofumi Nishi ◽  
Jun-ichi Iwata ◽  
Taichi Kosugi ◽  
Atsushi Oshiyama
Keyword(s):  
Bilayer Graphene ◽  
Energy Spectra ◽  
Two Dimensional ◽  
Twisted Bilayer Graphene

scholarly journals Robust zero modes in disordered two-dimensional honeycomb lattice with Kekulé bond ordering

2021 ◽  
pp. 168440
Author(s):  
Tohru Kawarabayashi ◽  
Yuya Inoue ◽  
Ryo Itagaki ◽  
Yasuhiro Hatsugai ◽  
Hideo Aoki
Keyword(s):  
Honeycomb Lattice ◽  
Two Dimensional ◽  
Zero Modes

scholarly journals Manipulation of hot carrier cooling dynamics in two-dimensional Dion–Jacobson hybrid perovskites via Rashba band splitting

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jun Yin ◽  
Rounak Naphade ◽  
Partha Maity ◽  
Luis Gutiérrez-Arzaluz ◽  
Dhaifallah Almalawi ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Phonon Scattering ◽  
Transient Absorption Spectroscopy ◽  
Band Model ◽  
Two Dimensional ◽  
Spintronic Devices ◽  
Hot Carrier ◽  
Band Splitting ◽  
Perovskite Materials ◽  
Spin Polarized

AbstractHot-carrier cooling processes of perovskite materials are typically described by a single parabolic band model that includes the effects of carrier-phonon scattering, hot phonon bottleneck, and Auger heating. However, little is known (if anything) about the cooling processes in which the spin-degenerate parabolic band splits into two spin-polarized bands, i.e., the Rashba band splitting effect. Here, we investigated the hot-carrier cooling processes for two slightly different compositions of two-dimensional Dion–Jacobson hybrid perovskites, namely, (3AMP)PbI4 and (4AMP)PbI4 (3AMP = 3-(aminomethyl)piperidinium; 4AMP = 4-(aminomethyl)piperidinium), using a combination of ultrafast transient absorption spectroscopy and first-principles calculations. In (4AMP)PbI4, upon Rashba band splitting, the spin-dependent scattering of hot electrons is responsible for accelerating hot-carrier cooling at longer delays. Importantly, the hot-carrier cooling of (4AMP)PbI4 can be extended by manipulating the spin state of the hot carriers. Our findings suggest a new approach for prolonging hot-carrier cooling in hybrid perovskites, which is conducive to further improving the performance of hot-carrier-based optoelectronic and spintronic devices.

scholarly journals Spectroscopy of a tunable moiré system with a correlated and topological flat band

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaomeng Liu ◽  
Cheng-Li Chiu ◽  
Jong Yeon Lee ◽  
Gelareh Farahi ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Band Structure ◽  
Twist Angle ◽  
Bilayer Graphene ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Flat Band ◽  
Correlated Electron ◽  
Partial Filling ◽  
Valley Polarization ◽  
Spectroscopic Signatures

AbstractMoiré superlattices created by the twisted stacking of two-dimensional crystals can host electronic bands with flat energy dispersion in which enhanced interactions promote correlated electron states. The twisted double bilayer graphene (TDBG), where two Bernal bilayer graphene are stacked with a twist angle, is such a moiré system with tunable flat bands. Here, we use gate-tuned scanning tunneling spectroscopy to directly demonstrate the tunability of the band structure of TDBG with an electric field and to show spectroscopic signatures of electronic correlations and topology for its flat band. Our spectroscopic experiments are in agreement with a continuum model of TDBG band structure and reveal signatures of a correlated insulator gap at partial filling of its isolated flat band. The topological properties of this flat band are probed with the application of a magnetic field, which leads to valley polarization and the splitting of Chern bands with a large effective g-factor.

Stability and superconductivity of Ca-intercalated bilayer blue phosphorene

2021 ◽  
Author(s):  
Artur Durajski ◽  
Kamil Skoczylas ◽  
Radoslaw Szczesniak
Keyword(s):  
Superconducting State ◽  
Potential Application ◽  
Recent Experiment ◽  
Superconducting Devices ◽  
Bilayer Graphene ◽  
Two Dimensional ◽  
Twisted Bilayer Graphene ◽  
Blue Phosphorene

Superconductivity attracts much interest in two-dimensional compounds due to their potential application in nano-superconducting devices. Inspired by a recent experiment reporting the superconducting state in twisted bilayer graphene, here, based...

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