Proof for the electronic band crossing in sliding bilayer graphene

2021 ◽  
Vol 104 (20) ◽  
Author(s):  
V. Nam Do
Keyword(s):  
Bilayer Graphene ◽  
Electronic Band ◽  
Band Crossing

scholarly journals Electronic band structure of magnetic bilayer graphene superlattices

2014 ◽  
Vol 116 (12) ◽  
pp. 123707 ◽  
Author(s):  
C. Huy Pham ◽  
T. Thuong Nguyen ◽  
V. Lien Nguyen
Keyword(s):  
Band Structure ◽  
Electronic Band Structure ◽  
Bilayer Graphene ◽  
Electronic Band

scholarly journals Moiréless correlations in ABCA graphene

2021 ◽  
Vol 118 (4) ◽  
pp. e2017366118 ◽  
Author(s):  
Alexander Kerelsky ◽  
Carmen Rubio-Verdú ◽  
Lede Xian ◽  
Dante M. Kennes ◽  
Dorri Halbertal ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Van Der Waals ◽  
Bilayer Graphene ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Van Hove Singularity ◽  
Natural Interfaces ◽  
Simple Material ◽  
Electronic Band ◽  
Topological Quantum

Atomically thin van der Waals materials stacked with an interlayer twist have proven to be an excellent platform toward achieving gate-tunable correlated phenomena linked to the formation of flat electronic bands. In this work we demonstrate the formation of emergent correlated phases in multilayer rhombohedral graphene––a simple material that also exhibits a flat electronic band edge but without the need of having a moiré superlattice induced by twisted van der Waals layers. We show that two layers of bilayer graphene that are twisted by an arbitrary tiny angle host large (micrometer-scale) regions of uniform rhombohedral four-layer (ABCA) graphene that can be independently studied. Scanning tunneling spectroscopy reveals that ABCA graphene hosts an unprecedentedly sharp van Hove singularity of 3–5-meV half-width. We demonstrate that when this van Hove singularity straddles the Fermi level, a correlated many-body gap emerges with peak-to-peak value of 9.5 meV at charge neutrality. Mean-field theoretical calculations for model with short-ranged interactions indicate that two primary candidates for the appearance of this broken symmetry state are a charge-transfer excitonic insulator and a ferrimagnet. Finally, we show that ABCA graphene hosts surface topological helical edge states at natural interfaces with ABAB graphene which can be turned on and off with gate voltage, implying that small-angle twisted double-bilayer graphene is an ideal programmable topological quantum material.

scholarly journals Enhanced third-harmonic generation by manipulating the twist angle of bilayer graphene

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Seongju Ha ◽  
Nam Hun Park ◽  
Hyeonkyeong Kim ◽  
Jiseon Shin ◽  
Jungseok Choi ◽  
...  
Keyword(s):  
Harmonic Generation ◽  
Incident Light ◽  
Twist Angle ◽  
Third Harmonic Generation ◽  
Optical Nonlinearity ◽  
Bilayer Graphene ◽  
Monolayer Graphene ◽  
Electronic Band ◽  
Third Harmonic ◽  
The Third

AbstractTwisted bilayer graphene (tBLG) has received substantial attention in various research fields due to its unconventional physical properties originating from Moiré superlattices. The electronic band structure in tBLG modified by interlayer interactions enables the emergence of low-energy van Hove singularities in the density of states, allowing the observation of intriguing features such as increased optical conductivity and photocurrent at visible or near-infrared wavelengths. Here, we show that the third-order optical nonlinearity can be considerably modified depending on the stacking angle in tBLG. The third-harmonic generation (THG) efficiency is found to significantly increase when the energy gap at the van Hove singularity matches the three-photon resonance of incident light. Further study on electrically tuneable optical nonlinearity reveals that the gate-controlled THG enhancement varies with the twist angle in tBLG, resulting in a THG enhanced up to 60 times compared to neutral monolayer graphene. Our results prove that the twist angle opens up a new way to control and increase the optical nonlinearity of tBLG, suggesting rotation-induced tuneable nonlinear optics in stacked two-dimensional material systems.

scholarly journals Visualization of the flat electronic band in twisted bilayer graphene near the magic angle twist

2020 ◽  
Author(s):  
M. Iqbal Bakti Utama ◽  
Roland J. Koch ◽  
Kyunghoon Lee ◽  
Nicolas Leconte ◽  
Hongyuan Li ◽  
...  
Keyword(s):  
Bilayer Graphene ◽  
Magic Angle ◽  
Electronic Band ◽  
Twisted Bilayer Graphene

scholarly journals Evolution of the electronic band structure of twisted bilayer graphene upon doping

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Shengqiang Huang ◽  
Matthew Yankowitz ◽  
Kanokporn Chattrakun ◽  
Arvinder Sandhu ◽  
Brian J. LeRoy
Keyword(s):  
Band Structure ◽  
Electronic Band Structure ◽  
Bilayer Graphene ◽  
Electronic Band ◽  
Twisted Bilayer Graphene

scholarly journals Angle-tunable intersubband photoabsorption and enhanced photobleaching in twisted bilayer graphene

Nano Research ◽  
2021 ◽  
Author(s):  
Eva A. A. Pogna ◽  
Xianchong Miao ◽  
Driele von Dreifus ◽  
Thonimar V. Alencar ◽  
Marcus V. O. Moutinho ◽  
...  
Keyword(s):  
Electronic Band Structure ◽  
Twist Angle ◽  
Interlayer Coupling ◽  
Bilayer Graphene ◽  
Relaxation Dynamics ◽  
Carrier Distribution ◽  
Absorption Bands ◽  
Electronic Band ◽  
Angle Dependence ◽  
Twisted Bilayer Graphene

AbstractVan der Waals heterostructures obtained by artificially stacking two-dimensional crystals represent the frontier of material engineering, demonstrating properties superior to those of the starting materials. Fine control of the interlayer twist angle has opened new possibilities for tailoring the optoelectronic properties of these heterostructures. Twisted bilayer graphene with a strong interlayer coupling is a prototype of twisted heterostructure inheriting the intriguing electronic properties of graphene. Understanding the effects of the twist angle on its out-of-equilibrium optical properties is crucial for devising optoelectronic applications. With this aim, we here combine excitation-resolved hot photoluminescence with femtosecond transient absorption microscopy. The hot charge carrier distribution induced by photo-excitation results in peaked absorption bleaching and photo-induced absorption bands, both with pronounced twist angle dependence. Theoretical simulations of the electronic band structure and of the joint density of states enable to assign these bands to the blocking of interband transitions at the van Hove singularities and to photo-activated intersubband transitions. The tens of picoseconds relaxation dynamics of the observed bands is attributed to the angle-dependence of electron and phonon heat capacities of twisted bilayer graphene.

scholarly journals Pressure-induced topological phase transition in noncentrosymmetric elemental tellurium

2019 ◽  
Vol 116 (51) ◽  
pp. 25530-25534 ◽  
Author(s):  
Toshiya Ideue ◽  
Motoaki Hirayama ◽  
Hiroaki Taiko ◽  
Takanari Takahashi ◽  
Masayuki Murase ◽  
...  
Keyword(s):  
Phase Transition ◽  
External Field ◽  
Topological Phase ◽  
Linear Dispersion ◽  
Electronic Band ◽  
Elemental Tellurium ◽  
Weyl Semimetal ◽  
Topological Phase Transition ◽  
Band Deformation ◽  
Band Crossing

Recent progress in understanding the electronic band topology and emergent topological properties encourage us to reconsider the band structure of well-known materials including elemental substances. Controlling such a band topology by external field is of particular interest from both fundamental and technological viewpoints. Here we report possible signatures of the pressure-induced topological phase transition from a semiconductor to a Weyl semimetal in elemental tellurium probed by transport measurements. Pressure variation of the periods of Shubnikov–de Haas oscillations, as well as oscillation phases, shows an anomaly around the pressure theoretically predicted for topological phase transition. This behavior is consistent with the pressure-induced band deformation and resultant band-crossing effect. Moreover, effective cyclotron mass is reduced toward the critical pressure, potentially reflecting the emergence of massless linear dispersion. The present result paves the way for studying the electronic band topology in well-known compounds and topological phase transition by the external field.

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