Time Delay in the Recoiling Valence Photoemission of Ar Endohedrally Confined inC60

Abstract

The effects of confinement and electron correlations on the relative time delay between the 3s and 3p photoemissions of Ar confined endohedrally in C60 are investigated using the time dependent local density approximation -a method that is also found to mostly agree with recent time delay measurements between the 3s and 3p subshells in atomic Ar. At energies in the neighborhood of 3p Cooper minimum, correlations with C60 electrons are found to induce opposite temporal effects in the emission of Ar 3p hybridized symmetrically versus that of Ar 3p hybridized antisymmetrically with C60. A recoil-type interaction model mediated by the confinement is found to best describe the phenomenon.PACS numbers: 32.80. Fb,With the tremendous advancement in technology for generating attosecond (as) isolated pulses as well as attosecond pulse trains, it becomes possible to study fundamental phenomena of light-matter interaction with unprecedented precision on an as timescale [1][2][3]. In particular, the relative time delay between the photoelectrons from different subshells on as timescale, a subject of intense recent activities, is expected to probe important aspects of electron correlations that predominantly influence the photoelectron. Pump-probe experiments have been performed to measure the relative delay in the photoemission processes, where extreme ultra-violet (XUV) pulses are used to remove an electron from a particular subshell and subsequently a weak infrared (IR) pulse accesses the temporal information of the emission event [4].Streaking measurements were carried out to probe photoemission from the valence and the conduction band in single-crystalline magnesium [5] and tungsten [6]. A streaking technique was also employed to measure the relative delay of approximately 21±5 as between the 2s and 2p subshells of atomic Ne at 106 eV photon energy [7]. Despite several theoretical attempts [8][9][10][11][12][13][14] to explain this measured delay in Ne, only about a half of the delay could be reproduced, keeping the time delay in Ne photoemissions still an open problem. Recently, the relative delay between the 3s and 3p subshells in Ar is measured at three photon energies by interferometric technique using attosecond pulses [15,16]. Theoretical methods (e.g. time-dependent nonperturbative method [8], diagrammatic many-body perturbation theory [13], Random phase approximation with exchange (RPAE) [14,16], and multi-configurational Hartree-Fock (MCHF) [17]) have been employed to investigate this relative delay in Ar, although agreements between theory and experiment is rather inconclusive. A ubiquitous understanding in all these studies is the dominant influence of electron correlations to determine the time behavior of outgoing electrons. Thus, it is fair to expect that the process near a Cooper minimum or a resonance will be particularly nuanced.It is therefore of spontaneous interest to extend the study to test the effect of correlations on the temporal photoresponse of atoms in material confinements. A brilliant natura...

Attosecond delay of xenon4dphotoionization at the giant resonance and Cooper minimum

“…Phase and Wigner-Smith delay calculations by us [25] using the time-dependent local-density approximation (TDLDA) have recently agreed very well with the experiment on argon 3p photorecombination around the 3p CM [16]. Correlated delays in the emission between atom-fullerene hybrid electrons near Cooper-type minima in the Ar@C 60 molecule were unraveled using TDLDA [22]. For a different variety of spectral minima, which are abundant in the photoemission of cluster systems, TDLDA has probed attosecond structures in the emission delay [26].…”

Attosecond chronoscopy of photoemission

“….) (6.4) giving rise to a modulation of the photoionization cross section (Rüdel et al, 2002) as well as of the EWS time delay Pazourek et al, 2013;Dixit et al, 2013;Nagele et al, 2014;Deshmukh et al, 2014). These modulations bear close resemblance to the extended xray absorption fine structure (EXAFS; Sayers et al, 1971;Stern and Heald, 1983;Ito et al, 2004) by the local crystallographic environment near an absorption site in condensed matter.…”

“…The situation is strikingly different for many-electron atoms. First experiments were performed for rare gas atoms (Schultze et al, 2010;Klünder et al, 2011;Guénot et al, 2012), the results of which have led to a flurry of theoretical investigations (Schultze et al, 2010;Kheifets and Ivanov, 2010;Komninos et al, 2011;Nagele et al, 2011Nagele et al, , 2012Nagele et al, , 2014Baggesen and Madsen, 2011;Zhang and Thumm, 2010;Ivanov and Smirnova, 2011;Dahlström et al, 2012bDahlström et al, , 2013Dahlström et al, , 2012aPazourek et al, 2012a,b;Śpiewanowski and Madsen, 2012;Pazourek et al, 2013;Moore et al, 2011;Carette et al, 2013;Kheifets, 2013;Dixit et al, 2013;Feist et al, 2014;Saha et al, 2014;Wätzel et al, 2015). Yet, satisfactory agreement between theory and experiment is still outstanding and many open questions remain.…”

“…These can have either positive or negative sign, depending on whether the phase jump is positive (+ ) or negative (− ). Photoionization of the Ar 3 electron with one radial node features a Cooper minimum at a photon energy XUV ≈ 45 eV already at the Hartree-Fock-level (Amusia, 1990;Starace, 2006) while strong 3 -3 intershell correlations are responsible for a deep Cooper minimum in the Ar 3 photoionization cross section near 42 eV (Dahlström et al, 2012a;Kheifets, 2013;Carette et al, 2013;Dixit et al, 2013;Dahlström and Lindroth, 2014;Saha et al, 2014). These photon energies are within reach of attosecond XUV pulses and have been investigated by combining an attosecond pulse train with an IR field.…”

“…Timing of the photoelectron emission from the central atom offers now to probe a multitude of environment-specific contributions to the time shift. For outer-shell electron emission, e.g., the 3 electron of argon, hybridization with the valence electrons of the C 60 shell strongly modifies the EWS time delay relative to that of the free atom (Dixit et al, 2013 (Kilcoyne et al, 2010;Dolmatov and Manson, 2008). The wavelength of the outgoing electron dB may match the resonance condition in terms of the radius of the fullerene shell 0 , = 2 0 , ( = 1, 2, .…”