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New class of excitons with hybrid dimensionality in layered silicon diphosphide

Nieuwe klasse van excitonen met hybride dimensionaliteit in gelaagd siliciumdifosfide2† aSchematic layered structure of SiP2Pnma, group number 62). It x,y,zcoordinate system is defined according to the crystal structure, as shown in the lower left corner. The blue shading marks the PB–PBchains formed by the PB-atoms in the ydirection of the crystal lattice, which play a critical role in the generation of quasi-1D electronic and excitonic states. bdtop view (b) and cross section (cd) STEM–ADF images of SiP2 viewed along the axis yc) and Xd† Green and cyan dotted rectangles represent the periodic grid with ABAB stacking order of SiP2layers. Scale bars, 1 nm. ebulk SiP . electronic band structure2 calculated based on the GW-method. The inset shows the first BZ of bulk SiP2† SiP2 is a semiconductor with an indirect band gap of 2.14 eV. The maximum of the valence band is at the Γ point and the minimum of the conduction band is along the Γ-Y ​​direction. The minimal conduction band state does not contribute to the formation of the A exciton due to the large direct interband transition energies at this location. f, distribution of the charge density of the edge of the conduction band (left) and the edge of the valence band (right) in real space. The iso-area of ​​the plot is 0.02 e3† Credit: Natural materials (2022). DOI: 10.1038/s41563-022-01285-3″ width=”800″ height=”404″/>

Crystal structure and band structure of layered SiP2aSchematic layered structure of SiP2Pnma, group number 62). The x,y,z coordinate system is defined according to the crystal structure, as shown in the lower left corner. The blue shading emphasizes the PB-PB chains formed by the PB atoms along the Yes direction of the crystal lattice, which play a critical role in the generation of quasi-1D electronic and excitonic states. bdTop view (b) and cross section (cd) STEM ADF images of SiP2 viewed along the Yes axis (c) and X axis (d† Green and cyan dotted rectangles represent the periodic grid with ABAB stacking order of SiP2 layers. Scale bars, 1 nm. eBulk SiP . Electronic Band Structure2 calculated from the GW method. The inset shows the first BZ of bulk SiP2† sip2 is a semiconductor with an indirect band gap of 2.14 eV. The maximum of the valence band is at the Γ point and the minimum of the conduction band is along the Γ-Y ​​direction. The minimal conduction band state does not contribute to the formation of the A exciton due to the large direct interband transition energies at this location. f, Charge density distribution of the conduction band edge (left) and the valence band edge (right) in real space. The iso-area of ​​the plot is 0.02 e3† Credit: Natural materials (2022). DOI: 10.1038/s41563-022-01285-3

Researchers from Nanjing University and Beihang University in China and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg, Germany, have produced a new class of excitons with hybrid dimensionality by testing the properties of layered silicon diphosphide (SiP₂). develop. † Their work has been published in Natural materials

Excitons are bound particles made up of a negatively charged electron and a positively charged electron hole. Their exotic behavior provides an important new platform to study the physics of materials when coupled with other states of matter, such as vibrations of the material’s crystal lattice.

Using SiP₂, researchers in China have fabricated a new kind of material whose 2D layers are bonded by van der Waals forces and exhibit strong internal covalent interactions. This produces peculiar one-dimensional phosphor chains along which electronic states can locate. The team then managed to develop a new kind of exciton with hybrid dimensionality in this layered material, meaning that the electron has 1D character and the hole shows 2D characteristics. This is the first time such a phenomenon has been observed. Theorists from the MPSD confirmed the findings with advanced simulations.

By exposing the material to laser light, the researchers were able to create and then investigate these excitonic states, which appear as peaks in the measured spectra. In particular, the emergence of a peculiar side peak at the main excitonic peak in the spectra shows a clear signature of the hybrid dimensionality excitons: due to their strong dependence on the internal structure of the material, the newly created excitons are expected to interact strongly with other material excitations, such as lattice vibrations that change the phosphorus chains in SiP₂.

The MPSD theory group then confirmed these findings through extensive analyses, using state-of-the-art methods to investigate the excitonic particles. Their simulations show that the particle consists of a positively charged hole of 2D character and a negatively charged electron located along the 1-dimensional phosphor chains, creating excitons with mixed dimensionality.

The theorists showed that such an exciton interacts strongly with lattice vibrations, generating the experimentally measured side peak characteristic. Such a feature has so far only been measured in low-dimensional materials such as graphene nanotubes or transition metal dichalcogenide monolayers, but not in a bulk material such as SiP₂.

This collaboration has demonstrated the existence of exciton-phonon sidebands in a 3D bulk crystal, as well as excitonic states with hybrid dimensionality. With scientists looking for new ways to monitor and investigate the interactions between quasiparticles such as excitons, phonons and others in solid materials, these findings represent an important advance.

“Our approach provides an intriguing platform to study and develop new states of matter such as trions (two electrons and one hole or vice versa) and more complex particles with hybrid dimensionality,” said co-author Peizhe Tang, a professor at Beihang University and visiting scientist at the MPSD.

Fellow co-author Lukas Windgätter, a doctoral student in the Institute’s Theory group, adds: “To me it is intriguing how one can control the interactions of particles through engineering solids. Especially being able to create composite particles with hybrid dimensionality opens avenues for new physics investigations.”


Tunable quantum traps for excitons


More information:
Ling Zhou et al, Unconventional excitonic states with phonon sidebands in layered silicon diphosphide, Natural materials (2022). DOI: 10.1038/s41563-022-01285-3

Provided by Max Planck Institute for the Structure and Dynamics of Matter


Quote: New class of excitons with hybrid dimensionality in layered silicon diphosphide (2022, June 20) retrieved June 20, 2022 from https://phys.org/news/2022-06-class-excitons-hybrid-dimensionality-layered.html

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