A new class of excitons with a hybrid dimension in layered silicon diphosphide

Нов клас екситони с хибридна размерност в слоест силициев дифосфид

Crystal structure and band structure of layered SiP2. orSchematic layered structure of SiP2 (Pnma, group number 62). IN x, y, z the coordinate system is determined by the crystal structure, as shown in the lower left corner. Blue shading emphasizes PB–PB chains formed by PB atoms along the d direction of the crystal lattice, which play a critical role in the generation of quasi-1D electronic and exciton states. beTop view (b) and cross section° C,e) STEM – ADF images on SiP2 viewed along d axis (° C) and x axis (e). The green and cyan dotted rectangles represent the periodic grid with ABAB order of SiP2 layers. Scale bands, 1 nm. eElectronic tape structure of bulk SiP2 calculated by GW method. The insertion shows the first BZ of the bulk SiP2. SiP2 is a semiconductor with an indirect band gap of 2.14 eV. The maximum of the valence band is at the point Γ, and the minimum of the conduction band is located in the direction Γ – Y. The minimum state of the conduction band does not contribute to the formation of A exciton due to the high direct energies of the interband transition at this point. is, Distribution of charge density at the edge of the conduction band (left) and the edge of the valence band (right) in real space. The isosurface of the graph is 0.02 e Å3. 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 Structure and Dynamics of Matter (MPSD) in Hamburg, Germany, have developed a new class of hybrid-sized excitons by designing the properties of layered silicon diphosphide (SiP₂). Their work is published in Natural materials.

Excitons are connected particles that consist of a negatively charged electron and a positively charged electron hole. Their exotic behavior offers an important new platform for studying the physics of materials when they are related to other states of matter, such as vibrations of the material. crystal lattice.

Using SiP₂, researchers in China have developed a new type of material whose 2D layers are bonded by van der Waals forces and have strong internal covalent interactions. This creates special one-dimensional phosphorus chains through which electronic states can be located. The team then managed to create a new type of exciton with a hybrid dimension in this multilayer material, which means that the electron has a 1D character and the hole shows 2D characteristics. This is the first time such a phenomenon has been observed. MPSD theorists have confirmed the findings with advanced simulations.

By exposing the material to laser light, the experimenters were able to create and subsequently study these excitonic states that appear as peaks in the measured spectra. In particular, the appearance of a special side peak to the main exciton peak in the spectra shows a distinct signature of excitons with hybrid dimension: Due to their strong dependence on the internal structure of the material, newly created excitons are expected to interact strongly with other material excitations such as lattice vibrations , which change the phosphorus chains in SiP2.

The theoretical group in MPSD subsequently confirmed these findings through extensive analysis using state-of-the-art exciton particle research methods. Their simulations show that the particle consists of a positively charged hole with a 2D character and a negatively charged electron, which is localized along the 1-dimensional phosphorus chains, generating excitons of mixed dimension.

Theorists demonstrate that such an exciton interacts strongly with lattice vibrations, which generates the experimentally measured lateral peak characteristic. Such a characteristic has so far been measured only in low-dimensional materials such as graphene nanotubes or monolayers of dichalcogenide transition metals, but not in bulk material such as SiP₂.

This cooperation has shown the existence of exciton-phonon sidebands in 3D bulk crystal, as well as exciton states with hybrid dimension. As scientists look for new ways to control and study the interactions between quasi-particles such as excitons, phonons, and others in solid materials, these findings represent important advances.

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

Co-author Lucas Windgater, a PhD student in the institute’s theory group, added: “It’s intriguing to me how one can control particle interactions through engineered solids. Especially the ability to create composite particles with a hybrid dimension opens the way to explore new physics. ”


Adjustable quantum exciton traps


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

Quote: A new class of excitons with a hybrid dimension in layered silicon diphosphide (2022, June 20), extracted on June 20, 2022 from https://phys.org/news/2022-06-class-excitons-hybrid-dimensionality- layered.html

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