By Pranjal Malewar 20 Aug, 2024
Collected at: https://www.techexplorist.com/scientists-uncovered-exciton-behavior-van-der-waals-magnets/87427/
Magnetic van der Waals (vdW) materials have opened new frontiers for realizing novel many-body phenomena. A research group led by scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory has uncovered details about the formation and behavior of van der Waals magnets.
Through this work, they established a picture of the complex relationship between these materials’ optical and magnetic properties.
Scientists used the National Synchrotron Light Source II (NSLS-II) to study a crystalline material, nickel-phosphorus trisulfide (NiPS3). The National Synchrotron Light Source II (NSLS-II)is a Brookhaven DOE Office of Science user facility that produces intense X-ray light beams.
An exciton consists of an electron and a “hole” bound together and moving as a unit. Excitons have been found in NiPS3, which has generated much interest in this specific van der Waals material. This is because there may be a substantial correlation between the excitons and the underlying magnetic structure, which raises the possibility of using magnetism to better understand and possibly even control excitons.
However, despite numerous investigations, scientists have not yet been able to determine the exciton motion and structure in NiPS3.
Scientists tackled this challenge using an X-ray technique known as resonant inelastic X-ray scattering (RIXS), available at NSLS-II’s Soft Inelastic X-ray Scattering (SIX) beamline. This cutting-edge experimental station was designed to use NSLS-II’s ultrabright X-ray beams to study the electronic properties of solid materials, revealing energy behaviors at a very high resolution.
In RIXS, X-ray photons hit electrons in a material and scatter in many directions. At SIX, scientists catch these scattered photons and measure their momentum and energy very precisely. Using special software from Brookhaven, they can analyze this data to learn about the material’s electrons and holes.
They discovered that excitons form and move around in the NiPS3 crystal based on a principle called Hund’s exchange interaction. This principle affects the energy levels of different electron spin configurations. In NiPS3, Hund’s exchange gives the exciton the energy it needs to form.
Scientists found that the exciton behaves like a “double-magnon,” another quasiparticle, in how it spreads across the crystal. Magnons, which are collective excitations of electron spins in a crystal lattice, are an additional aspect of the combined electronic and magnetic behaviors of van der Waals magnets.
Postdoctoral researcher and first author of the study Wei He said, “In the coming years, as instrumentation and techniques like RIXS and electron microscopy are further developed, we expect to be able to take even better measurements of NiPS3. We believe that this material has outstanding potential for opening a pathway for using magnetic Hund’s excitons to realize new forms of controllable magnetic information.”
Journal Reference:
- He, W., Shen, Y., Wohlfeld, K. et al. Magnetically propagating Hund’s exciton in van der Waals antiferromagnet NiPS3. Nat Commun 15, 3496 (2024). DOI: 10.1038/s41467-024-47852-x
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