Related Experiment Video
Updated: Dec 28, 2025
11:24
Optimized Fabrication Procedure for High-Quality Graphene-based Moiré Superlattice Devices
Published on: July 11, 2025
14.4K
Flat bands and gaps in twisted double bilayer graphene
F J Culchac1, R R Del Grande1, Rodrigo B Capaz1
1Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972, Brazil.
Nanoscale
|February 18, 2020
Summary
Twisted double bilayer graphene (TDBG) exhibits a tunable band gap dependent on twist angle and electric fields. Surface effects and localized states influence this band gap, particularly at low twist angles where flat bands emerge.
Area of Science:
- Condensed matter physics
- Materials science
- Nanotechnology
Background:
- Graphene and its layered structures offer unique electronic properties.
- Twisted bilayer graphene (TBG) has shown promise for tunable electronic behavior.
- Understanding tetralayer graphene structures like TDBG is crucial for advanced electronic applications.
Purpose of the Study:
- To investigate the electronic structure of twisted double bilayer graphene (TDBG).
- To determine the factors influencing the band gap in TDBG.
- To explore the effect of twist angle and electric fields on TDBG properties.
Main Methods:
- First-principles electronic structure calculations.
- Analysis of band gap dependence on twist angle.
- Investigation of electric field effects on TDBG.
Main Results:
- TDBG exhibits a semiconducting nature with an angle-dependent band gap.
- The band gap can be tuned by an external electric field.
- Surface effects and localized states at inner layers dictate band gap magnitude and angle dependence.
- Low twist angles lead to reduced band gaps and the formation of flat bands.
Conclusions:
- TDBG presents a tunable electronic platform with potential for novel device applications.
- The interplay of surface effects and localized states is key to understanding TDBG's electronic properties.
- Flat band formation at low twist angles opens possibilities for correlated electron phenomena.
Related Concept Videos
01:01Energy Bands in Solids
1.7K
Isolated atoms have discrete energy levels that are well described by the Bohr model. And, it quantifies the energy of an electron in a hydrogen atom as En. Higher quantum numbers 'n' yield less negative, closer electron energy levels.
Band Formation:
When atoms are brought close together, as in a solid, these discrete energy levels begin to split due to the overlap of electron orbitals from adjacent atoms. This split occurs because of the Pauli exclusion principle, which states...
Band Formation:
When atoms are brought close together, as in a solid, these discrete energy levels begin to split due to the overlap of electron orbitals from adjacent atoms. This split occurs because of the Pauli exclusion principle, which states...
1.7K
02:35Band Theory
16.9K
When two or more atoms come together to form a molecule, their atomic orbitals combine and molecular orbitals of distinct energies result. In a solid, there are a large number of atoms, and therefore a large number of atomic orbitals that may be combined into molecular orbitals. These groups of molecular orbitals are so closely placed together to form continuous regions of energies, known as the bands.
The energy difference between these bands is known as the band gap.
Conductor, Semiconductor,...
The energy difference between these bands is known as the band gap.
Conductor, Semiconductor,...
16.9K
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
47.6K
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
47.6K
01:08IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations
1.7K
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single...
1.7K