An article published in Nature Communications (see Nat. Comm. 2018, 9, 955, DOI: 10.1038/s41467-018-03009-1) has identified the role of autoionizing resonances in photoemission time delays, a clear manifestation of electron correlation effects on photoionization processes. The work results from an international cooperation among researchers led by U. Keller (ETH-Zurich), F. Martín (Universidad Autonoma de Madrid, IFIMAC Condensed Matter Center and IMDEA-Nanoscience), and A. L’Hullier (Lund University).
Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the continuum spectrum of atomic and molecular targets, is mediated by electron correlation. The paper investigates the attosecond photoemission dynamics in argon in the 20–40 eV spectral range, in the vicinity of the 3s−1np autoionizing resonances. Measurements of the differential photoionization cross section are reported, from which energy and angle-dependent atomic time delays are extracted with an attosecond interferometric method. With the support of a theoretical model, a large part of the measured time delay anisotropy is attributed to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
Figure: Anisotropic photoemission time delays close to a Fano resonance.
Angular-resolved time delays. (a) and (b) show the measured atomic time delay as a function of electron emission angle in the absence and the presence of an autoionizing state, respectively (red and blue symbols). The delays are referenced to the value retrieved for electrons departing within an opening angle of up to 30 degrees. The green lines show the calculated delays in resonant (solid) and nonresonant (dashed) conditions. The error bars indicate the standard deviation as extracted by a series of independent measurements.
Source: Nat. Comm. 2018, 9, 955, DOI: 10.1038/s41467-018-03009-1