24-Jun-2022 - Max-Planck-Institut für Struktur und Dynamik der Materie

New class of excitons with hybrid dimensionality in layered silicon diphosphide

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 exciton with hybrid dimensionality by engineering the properties of layered silicon diphosphide (SiP₂). Their work has been published in Nature Materials.

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

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

By exposing the material to laser light, the experimentalists were able to create and subsequently probe these exitonic states, which appear as peaks in the measured spectra. In particular, the emergence of a peculiar side peak to the main excitonic peak in the spectra shows a distinct signature of the hybrid dimensionality excitons: Due to their strong dependence on the material’s internal structure, the newly-created excitons are expected to interact strongly with other material excitations, such as lattice vibrations that alter the phosphorous chains in SiP₂.

The theory group at the MPSD subsequently confirmed these findings through extensive
analysis, using state-of-the-art methods to investigate the excitonic particles. Their simulations show that the particle consists of a positively charged hole with 2D character and a negatively charged electron that is localized along the 1-dimensional phosphorous chains, giving rise to excitons with mixed dimensionality.

The theoreticians demonstrated that such an exciton interacts strongly with lattice vibrations, which generates the experimentally measured side peak feature. 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 shown 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 control and investigate the interactions between quasi-particles such as excitons, phonons and others in solid materials, these findings represent important progress.

“Our approach provides an intriguing platform to study and engineer new states of matter such as trions (two electrons and one hole or vice versa) and more complex particles with hybrid dimensionality,” says co-author Peizhe Tang, 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 up pathways to investigate new physics.”

Facts, background information, dossiers
  • excitons
More about Max-Planck-Institut für Struktur und Dynamik der Materie
More about Max-Planck-Gesellschaft
  • News

    Better magnets for green energy

    Soft magnetic materials (SMMs) applied in electric engines transform energy from sustainable resources into electricity. Conventional SMMs, which are currently used in industry, are prone to damage under severe mechanical loads. Researchers from the Max-Planck-Institut für Eisenforschung (M ... more

    High harmonics illuminate the movement of atoms and electrons

    Laser light can radically change the properties of solid materials, making them superconducting or magnetic within millionths of a billionth of a second. The intense light causes fundamental, immediate changes in a solid by ‘shaking’ its atomic lattice structure and moving electrons about. ... more

    A Sanitizer in the Galactic Centre Region

    An international group of researchers led by Arnaud Belloche (MPIfR, Bonn, Germany) reports the first identification iso-propanol in interstellar space, a substance which is used as a sanitizer on Earth. Iso-propanol is the largest alcohol detected so far, demonstrating the increasing compl ... more

More about Nanjing University
  • News

    New 3D chirality discovered and synthetically assembled

    The origin of lives of human beings, animals and plants on earth is attributed to chirality because it is necessitated for the formation of biomolecules, such as nucleic acids, proteins, carbohydrates, etc. The studies on chirality have been becoming increasingly active and extensive due to ... more

    4D imaging with liquid crystal microlenses

    Most images captured by a camera lens are flat and two dimensional. Increasingly, 3D imaging technologies are providing the crucial context of depth for scientific and medical applications. 4D imaging, which adds information on light polarization, could open up even more possibilities, but ... more

    All in one against CO2

    A "self-heating" boron catalyst that makes particularly efficient use of sunlight to reduce carbon dioxide (CO2) serves as a light harvester, photothermal converter, hydrogen generator, and catalyst in one. Researchers introduce a photothermocatalytic reaction that requires no additives bey ... more

More about Beihang University
  • News

    Microtube with Built-In Pump

    Driven by natural or artificial sunlight, a novel “microtube pump” transports water droplets over long distances. As reported by Chinese researchers in the Journal Angewandte Chemie, the pump consists of a tube whose properties can be changed asymmetrically through irradiation. This results ... more

    Revealing high performance CNT catalyst relating to its electroconductivity

    Recent research showed biofuels were obtained from Jatropha Oil using carbon nanotube (CNT) catalyst, which showed efficient cracking activity. The performance was activated by the high stability, metal sites, acid sites, electroconductivity, and coking tolerance of CNT. Two cracking circul ... more

    What makes penguin feathers ice-proof

    Humboldt penguins live in places that dip below freezing in the winter, and despite getting wet, their feathers stay sleek and free of ice. Scientists have now figured out what could make that possible. They report that the key is in the microstructure of penguins' feathers. Based on their ... more