Draft:Time autocorrelation of auxiliary wavefunctions (TACAW) method
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Comment: Possibly a question of WP:TOOSOON. Stuartyeates (talk) 23:15, 25 July 2025 (UTC)
Time Autocorrelation of Auxiliary Wavefunctions (TACAW)[1] is a theoretical method developed to simulate angle-resolved electron energy loss and gain spectroscopies (EELS and EEGS) in scanning transmission electron microscopy (STEM), particularly for low-energy excitations such as phonons and magnons. The approach captures multiple scattering effects, temperature dependence, and dynamical diffraction while maintaining computational efficiency and scalability.
Overview
[edit]The TACAW method was introduced in 2025 by José Ángel Castellanos-Reyes, Paul M. Zeiger, and Ján Rusz, researchers at Uppsala University, in response to the increasing need for a rigorous and general theoretical framework to interpret high-resolution electron spectroscopies of lattice and spin excitations at the nanoscale.
Methodology
[edit]TACAW is based on the quantum excitation of phonons (QEP) model and extends it to provide momentum- and energy-resolved spectra. The key principle involves calculating the time autocorrelation of an auxiliary electron beam wavefunction, from multislice simulations, which is propagated through atomistic configurations obtained from molecular dynamics (MD) or atomistic spin dynamics (ASD) simulations. These time-dependent auxiliary wavefunctions are then Fourier transformed from the time to energy domain to yield energy-resolved scattering spectra.
Key features
[edit]- Multiple scattering: Includes both single and multiple inelastic scattering events.
- Dynamical diffraction: Accounts for the coherent evolution of the electron wavefunction in the crystal.
- Momentum-resolved simulations: Produces full EELS and EEGS spectra.
- Computational efficiency: Designed to run efficiently on parallel computing architectures.
Applications
[edit]Phonon spectroscopy
[edit]TACAW was first applied to simulate vibrational spectra in materials such as silicon and hexagonal boron nitride (hBN), accurately reproducing features such as phonon band dispersions and multiphonon contributions. The method captures both energy loss and gain channels, yielding results consistent with advanced frozen-phonon simulations while offering improved handling of multiple scattering and thermal effects.
Magnon spectroscopy
[edit]The TACAW formalism was later extended to simulate magnon excitations by analogy with phonons. In this context, magnetic moment tilts replace atomic displacements, and auxiliary wavefunctions are calculated using magnetic multislice methods. In 2025, TACAW was used to support the interpretation of the first direct STEM-EELS observation of propagating magnons inside antiferromagnetic nanocrystals, marking a milestone in nanoscale magnetic spectroscopy.[2]
Scientific impact
[edit]The introduction of TACAW represents a significant theoretical advance in electron microscopy.[3] It enables the quantitative simulation of ultralow-energy electron spectroscopies in a broad range of materials and geometries,[1][4] [5]and it has already been instrumental in the analysis of experiments on vibrational and magnetic excitations at the atomic scale.[2][1][6][7]
See also
[edit]- Electron energy loss spectroscopy
- Scanning transmission electron microscopy
- Magnonics
- Spin wave
- Phonon
- Spintronics
References
[edit]- ^ a b c Castellanos-Reyes, José Ángel; Zeiger, Paul M.; Rusz, Ján (2025-01-22). "Dynamical Theory of Angle-Resolved Electron Energy Loss and Gain Spectroscopies of Phonons and Magnons in Transmission Electron Microscopy Including Multiple Scattering Effects". Physical Review Letters. 134 (3): 036402. arXiv:2401.15599. Bibcode:2025PhRvL.134c6402C. doi:10.1103/PhysRevLett.134.036402. PMID 39927933.
- ^ a b Kepaptsoglou, Demie; Castellanos-Reyes, José Ángel; Kerrigan, Adam; Alves do Nascimento, Júlio; Zeiger, Paul M.; El hajraoui, Khalil; Idrobo, Juan Carlos; Mendis, Budhika G.; Bergman, Anders; Lazarov, Vlado K.; Rusz, Ján; Ramasse, Quentin M. (2025-07-23). "Magnon spectroscopy in the electron microscope". Nature: 1–6. doi:10.1038/s41586-025-09318-y. ISSN 1476-4687. PMID 40702193.
- ^ "New Theory to Explore Atomic and Magnetic Vibrations at the Nanoscale - Uppsala University". www.uu.se. 2025-01-24. Retrieved 2025-07-25.
- ^ Mao, Ruilin; He, Peiyi; Liu, Fachen; Shi, Ruochen; Du, Jinlong; Gao, Peng (2025-06-10). "Electron Microscopy for Nanophononics: A Review". ACS Nano. 19 (22): 20269–20294. doi:10.1021/acsnano.4c17750. ISSN 1936-0851. PMID 40415637.
- ^ Haas, Benedikt; Koch, Christoph T.; Rez, Peter (2024-10-10). "Perspective on atomic-resolution vibrational electron energy-loss spectroscopy". Applied Physics Letters. 125 (15): 150502. arXiv:2408.09148. Bibcode:2024ApPhL.125o0502H. doi:10.1063/5.0231688. ISSN 0003-6951.
- ^ "Press releases - Uppsala University". www.uu.se. 2024-03-19. Retrieved 2025-07-25.
- ^ University, Uppsala. "Spin waves observed directly at nanoscale for first time". phys.org. Retrieved 2025-07-25.
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