Related Experiment Video
Updated: Jul 2, 2026
08:04
Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Alterexciton: Single-Valley Dipolar Excitons in Noncentrosymmetric Monolayer
Jingda Guo1, Hongyan Ji1, Shuyi He1
1MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices & School of Integrated Circuits and Electronics, Beijing Institute of Technology, Beijing 100081, China.
ACS Nano
|June 30, 2026
Summary
Researchers discovered a new type of exciton, the alterexciton, in a single material layer. This discovery enables electrical control over excitonic polarization and opens pathways for novel quantum emitters.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Optics
Background:
- Dipolar excitons usually form in van der Waals heterostructures (vdWHs) with electrons and holes in separate layers.
- Tunability of these excitons is limited by built-in fields and nonradiative decay.
Purpose of the Study:
- To propose and investigate a novel dipolar exciton, the alterexciton, within a single layer of Hf2SiCO2.
- To explore the electrical tunability and unique properties of these single-layer excitons.
Main Methods:
- Theoretical proposal of alterexcitons in monolayer Hf2SiCO2.
- Analysis of electronic band structure and exciton properties.
- Investigation of optical selection rules and Berry curvature effects.
Main Results:
- Introduced the 'alterexciton' with alternating dipole moments in two X valleys within a single atomic layer.
- Demonstrated electrically tunable polarization and single-valley excitonic insulator behavior.
- Observed linear dichroism, valley-dependent tunability, and the exciton Hall effect.
Conclusions:
- Alterexcitons offer a new platform for valley-polarized exciton manipulation.
- These findings pave the way for developing single-valley, single-photon emitters.
Related Concept Videos
04:01VSEPR Theory and the Effect of Lone Pairs
Effect of Lone Pairs of Electrons on Molecule Geometry
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
01:11P-N junction
A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...
01:28Induced Electric Dipoles
A permanent electric dipole orients itself along an external electric field. This rotation can be quantified by defining the potential energy because the external torque does work in rotating it. Then, the potential energy is minimum at the parallel configuration and maximum at the antiparallel configuration. While the former is a stable equilibrium, the latter is an unstable equilibrium.
Since the absolute value of potential energy holds no physical meaning, its zero value can be chosen as per...
Since the absolute value of potential energy holds no physical meaning, its zero value can be chosen as per...
01:04IR Absorption Frequency: Delocalization
Electron delocalization refers to the distribution of electrons across multiple atoms within a molecule rather than being confined to a single atom or bond. This phenomenon is common in systems with conjugated bonds—structures where alternating single and double bonds allow π-electrons to move freely across the network. The movement of electrons stabilizes the molecule and can affect various chemical properties, including vibrational frequencies observed in IR spectroscopy.
In IR spectroscopy,...
In IR spectroscopy,...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
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,...