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Spin-orbit and angle-resolved resonant attosecond photoionization delays

D. Biswas1, J. K. Wood2, N. Chakraborty1, A. S. Kheifets3, and A. Sandhu1,2,4,*

  • *Contact author: asandhu6@asu.edu
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Phys. Rev. Research 8, 023058 – Published 17 April, 2026

DOI: https://doi.org/10.1103/qfch-b1cv

Abstract

Understanding how spin-orbit coupling shapes ultrafast electron dynamics remains a central challenge across atomic, molecular, and condensed-matter systems. Here, we demonstrate that spin-orbit splitting in krypton naturally separates two distinct regimes of attosecond interferometry: a conventional above-threshold process involving interference between continuum pathways and an under-threshold regime in which discrete and continuum intermediate states coexist and interfere. Using spin-orbit and angle-resolved measurements with attosecond precision, supported by ab initio time-dependent simulations, we reveal that the under-threshold channel exhibits dramatic phase and delay variations—up to several hundred attoseconds—highly sensitive to photon energy and emission direction. In contrast, the conventional above-threshold channel shows smooth, featureless behavior. This duality exposes the strong influence of metastable resonances, establishing spin-orbit splitting as a built-in control knob for accessing structured continua. Beyond krypton, our results provide a broadly applicable framework for probing and controlling coupled spin, orbital, and many-body correlation dynamics at the attosecond timescale.

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Phys. Rev. Research 8, 023058– Published 17 April, 2026
  • Received 9 November 2025
  • Accepted 22 March 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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