toplogo
Sign In

Probing Orbital Skyrmion Textures in Twisted TMDs via Bulk Plasmons: A Theoretical Study


Core Concepts
While traditional Bloch-band Berry curvature doesn't affect bulk plasmons, this study reveals that these plasmons can serve as probes for real-space topology, particularly orbital Skyrme textures in twisted transition metal dichalcogenides (TMDs).
Abstract

Bibliographic Information:

Cavicchi, L., Reijnders, K. J. A., Katsnelson, M. I., & Polini, M. (2024). Optical properties, plasmons, and orbital Skyrme textures in twisted TMDs. arXiv preprint arXiv:2410.18025.

Research Objective:

This study investigates the impact of real-space topology, specifically orbital Skyrme textures, on the optical and plasmonic properties of twisted transition metal dichalcogenide (TMD) bilayers. The researchers aim to demonstrate that bulk plasmons can serve as a probe for these topological features.

Methodology:

The researchers employ a combination of theoretical approaches, including:

  • Collisionless hydrodynamic equations to analyze the influence of Berry curvature on plasmons.
  • Continuum models, specifically skyrmion Chern-band models, to describe the topological moiré bands of twisted TMD homobilayers.
  • Kubo formula to calculate the local optical conductivity tensor.
  • Random phase approximation (RPA) to determine the energy loss function and analyze collective modes.
  • Semiclassical techniques to project the Hamiltonian onto a single layer-pseudospin sector, enabling a mapping onto a Landau-level problem.

Key Findings:

  • While Bloch momentum-space Berry curvature doesn't influence long-wavelength bulk plasmons, real-space topology induced by orbital Skyrme lattices does.
  • The presence of an orbital skyrmion lattice leads to a finite Hall-like conductivity in the single-valley and single-spin sector, originating from the orbital magnetic moment of the Bloch states.
  • The energy loss function reveals gapped and slow collective modes, resembling magnetoplasmons, which are attributed to the flatness of the moiré bands and the presence of the orbital Skyrme lattice.
  • The study demonstrates that the plasmon gap at zero wave number is approximately related to the uniform component of the skyrmion effective magnetic field.

Main Conclusions:

The research concludes that bulk plasmons in twisted TMD bilayers can effectively probe orbital Skyrme textures. The gapped behavior of these plasmons is linked to the effective magnetic field arising from the skyrmion lattice. While an effective magnetic field description provides a qualitative understanding, accurate quantitative results necessitate a comprehensive quantum treatment.

Significance:

This study significantly contributes to the understanding of the interplay between real-space topology and the optical and plasmonic properties of twisted TMDs. The findings have implications for the development of novel optoelectronic and plasmonic devices based on these materials.

Limitations and Future Research:

The study primarily focuses on the long-wavelength limit and utilizes the RPA, which might not fully capture the complexities of strongly correlated systems. Future research could explore non-perturbative approaches, such as exact diagonalization or the Bijl-Feynman single-mode approximation, to account for strong electron-electron interactions. Additionally, investigating the impact of real-space variations in the skyrmion magnetic field on non-local corrections to the plasmon dispersion at finite wave vectors is crucial for a more complete understanding.

edit_icon

Customize Summary

edit_icon

Rewrite with AI

edit_icon

Generate Citations

translate_icon

Translate Source

visual_icon

Generate MindMap

visit_icon

Visit Source

Stats
The twist angle used in the simulations for twisted MoTe2 is 3.1 degrees. The first interband transition energy (ℏω01) is approximately 8 meV. The second interband transition energy (ℏω02) is approximately 33 meV. The estimated cyclotron frequency (ℏωc) for θ = 3.1° is approximately 19 meV. The ratio of electron-electron interaction energy scale to the effective cyclotron energy is estimated to be approximately 65/ε, where ε is the dielectric permittivity.
Quotes

Deeper Inquiries

How would the incorporation of excitonic effects, which are significant in TMDs, modify the plasmonic properties and their relation to the orbital Skyrme textures?

Incorporating excitonic effects would significantly enrich the interplay between plasmons and orbital Skyrme textures in twisted TMDs. Here's how: Modification of Plasmon Dispersion: Excitons, being bound electron-hole pairs, introduce a new energy scale and modify the dielectric function of the material. This alteration leads to a renormalization of the plasmon frequency and can even result in the emergence of new plasmon modes, such as exciton-polariton modes, arising from the strong coupling between excitons and plasmons. Influence on Skyrmion-Induced Gap: The presence of excitons can influence the gap in the plasmon spectrum arising from the orbital Skyrme texture. The effective dielectric screening provided by the exciton gas can reduce the effective Coulomb interaction, thereby modifying the magnitude of the gap. Additionally, the interplay between the exciton Bohr radius and the moiré length scale can lead to intriguing effects on the plasmon gap. Emergence of Novel Exciton-Skyrmion Coupling: The interplay between excitons and the orbital Skyrme texture could give rise to novel physical phenomena. For instance, excitons, with their finite spatial extent, could couple to the spatially varying effective magnetic field induced by the Skyrmion texture. This coupling could lead to a modulation of the exciton energy levels and potentially enable the manipulation of excitonic properties via the Skyrme texture. Impact on Experimental Observables: The modified plasmon dispersion and the altered plasmon gap due to excitonic effects would be directly observable in experiments like scattering-type near-field optical spectroscopy. These observations could provide valuable insights into the nature of exciton-plasmon coupling and its interplay with the real-space topology of the system. In summary, incorporating excitonic effects is crucial for a complete understanding of the plasmonic properties in twisted TMDs and their relationship with orbital Skyrme textures. This interplay opens up exciting avenues for exploring novel physical phenomena and potential applications in optoelectronic devices.

Could the presence of defects or strain in the twisted TMD bilayer disrupt the orbital Skyrme textures and consequently alter the observed plasmonic behavior?

Yes, defects and strain can significantly disrupt the delicate orbital Skyrme textures in twisted TMD bilayers, leading to observable changes in the plasmonic behavior. Here's a breakdown: Disruption of Skyrmion Textures: Defects: Point defects, vacancies, or impurities can locally modify the interlayer coupling and potential landscape, directly influencing the delicate balance that stabilizes the Skyrmion texture. This disruption can lead to pinning of the Skyrmion lattice, formation of domain walls, or even complete annihilation of Skyrmions in the vicinity of the defect. Strain: Strain, either compressive or tensile, can alter the lattice constant and introduce anisotropy in the system. This modification directly impacts the moiré pattern and the interlayer hybridization, potentially distorting or even unwinding the Skyrmion texture. Impact on Plasmonic Properties: Shift in Plasmon Frequency: The disruption of the Skyrmion texture alters the effective periodic potential experienced by electrons. This change modifies the electronic band structure and consequently shifts the frequency of the interband plasmon modes. Broadening of Plasmon Peaks: Defects and strain introduce scattering centers for plasmons, leading to a decrease in their lifetime. This reduction in lifetime manifests as a broadening of the plasmon peaks observed in experiments like electron energy loss spectroscopy or scattering-type near-field optical spectroscopy. Emergence of Localized Plasmon Modes: Defects can act as trapping sites for plasmons, leading to the emergence of localized plasmon modes. These localized modes have frequencies distinct from the bulk plasmon modes and can be spatially imaged using near-field techniques. Experimental Implications: The sensitivity of plasmonic properties to defects and strain makes them valuable probes for characterizing the quality of twisted TMD samples. By intentionally introducing controlled defects or strain, one could potentially engineer the plasmonic response of these materials for specific applications. In conclusion, defects and strain can significantly impact the orbital Skyrme textures and consequently alter the observed plasmonic behavior in twisted TMD bilayers. This sensitivity highlights the importance of material quality and the potential for engineering plasmonic properties through controlled introduction of defects or strain.

What are the potential applications of utilizing bulk plasmons as probes for real-space topology in other material systems beyond twisted TMDs?

The utilization of bulk plasmons as probes for real-space topology extends beyond twisted TMDs, offering exciting possibilities in various material systems: Unconventional Superconductors: In unconventional superconductors, the pairing mechanism often involves a spatially modulated order parameter, leading to real-space topological defects like vortices or domain walls. Bulk plasmons, sensitive to the local electronic structure and dielectric properties, could be employed to probe the spatial arrangement and dynamics of these topological defects. Topological Magnetic Materials: Materials hosting magnetic skyrmions, merons, or other non-trivial spin textures offer a fertile ground for plasmonic investigations. The spatially varying magnetization in these materials can couple to the plasmon modes, leading to unique signatures in their dispersion and providing insights into the underlying magnetic topology. Ferroelectric Domain Walls: Ferroelectric materials exhibit domains with different polarization orientations separated by domain walls. These walls can host exotic electronic states and topological defects. Bulk plasmons, sensitive to the local dielectric permittivity, could be utilized to map the domain wall configurations and probe the electronic properties at these interfaces. Excitonic Insulators and Topological Excitons: In materials exhibiting excitonic condensation or hosting topological excitons, the real-space distribution of excitons and their interactions can be probed using plasmons. The formation of excitonic condensates or the presence of excitonic vortices would lead to distinct modifications in the plasmonic response. Engineered Metasurfaces and Metamaterials: By designing artificial periodic structures or metamaterials with tailored optical properties, one can create synthetic gauge fields and induce non-trivial topological phases. Bulk plasmons in these engineered systems can be used to probe the emergent topological properties and their dependence on the structural design. The key advantages of utilizing bulk plasmons as probes lie in their sensitivity to local electronic structure, dielectric properties, and their ability to be probed with high spatial resolution using near-field techniques. This approach opens up exciting avenues for exploring and manipulating real-space topology in a wide range of quantum materials and engineered systems, with potential applications in next-generation electronic, optoelectronic, and spintronic devices.
0
star