Spectral density of angular momentum transfer from a swift electron to a large spherical nanoparticle
Abstract
Swift electrons in scanning transmission electron microscopy transfer both linear and angular momentum to nanoparticles, underlying electron-beam-driven nanoscale manipulation ("electron tweezers"). Prior theory relied either on the small-particle (dipolar) approximation, valid only well below experimentally relevant sizes, or on frequency-integrated multipolar calculations that leave the spectral structure of the interaction unresolved. Here we present a fully retarded, causal, multipole-converged electrodynamical methodology for the angular momentum transfer from a swift electron to an isolated spherical nanoparticle, based on a closed-surface Maxwell stress tensor formulation whose angular integrals reduce analytically to a small, material- and trajectory-independent set of irreducible integrals over associated Legendre functions. This lowers the cost of the double multipolar sum, enabling convergence up to l_max=51 for nanoparticles as large as a=50 nm, nearly four times the order of the largest previous calculation at this size and previously unreached for an optically complex, interband-dominated material. Applied to aluminum and gold nanoparticles up to a=50 nm, the method resolves the transfer spectral density across the full frequency domain, showing it is set by interference between the electron field and the field scattered by the nanoparticle, which dominates the scattered-scattered contribution at essentially every frequency; the electric contribution dominates at moderate speeds, but the magnetic contribution, of the same sign, grows steadily in relative weight with electron speed, from a few percent of the total at v = 0.5c to between a quarter and a half of it at v = 0.95c for trajectories passing close to the nanoparticle surface.
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BibTeX
@misc{brisenogomez2026spectral,
title = {{Spectral density of angular momentum transfer from a swift electron to a large spherical nanoparticle}},
author = {Jorge Luis Briseño-Gómez and Alejandro Reyes-Coronado},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.14319},
eprint = {2609.14319},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.14319},
}
RIS
TY - UNPB
TI - Spectral density of angular momentum transfer from a swift electron to a large spherical nanoparticle
AU - Jorge Luis Briseño-Gómez
AU - Alejandro Reyes-Coronado
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2609.14319
UR - https://arxiv.org/abs/2609.14319
AB - Swift electrons in scanning transmission electron microscopy transfer both linear and angular momentum to nanoparticles, underlying electron-beam-driven nanoscale manipulation ("electron tweezers"). Prior theory relied either on the small-particle (dipolar) approximation, valid only well below experimentally relevant sizes, or on frequency-integrated multipolar calculations that leave the spectral structure of the interaction unresolved. Here we present a fully retarded, causal, multipole-converged electrodynamical methodology for the angular momentum transfer from a swift electron to an isolated spherical nanoparticle, based on a closed-surface Maxwell stress tensor formulation whose angular integrals reduce analytically to a small, material- and trajectory-independent set of irreducible integrals over associated Legendre functions. This lowers the cost of the double multipolar sum, enabling convergence up to l_max=51 for nanoparticles as large as a=50 nm, nearly four times the order of the largest previous calculation at this size and previously unreached for an optically complex, interband-dominated material. Applied to aluminum and gold nanoparticles up to a=50 nm, the method resolves the transfer spectral density across the full frequency domain, showing it is set by interference between the electron field and the field scattered by the nanoparticle, which dominates the scattered-scattered contribution at essentially every frequency; the electric contribution dominates at moderate speeds, but the magnetic contribution, of the same sign, grows steadily in relative weight with electron speed, from a few percent of the total at v = 0.5c to between a quarter and a half of it at v = 0.95c for trajectories passing close to the nanoparticle surface.
ER -