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DTSTART;TZID=Europe/Paris:20220530T140000
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DTSTAMP:20220407T093200
UID:MEC-90f1f4972d133619a60c30f3559ec0c5@lps.u-psud.fr
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SUMMARY:Mauro Fanciulli | Spin, orbit and time-resolved spectroscopieson transition metal dichalcogenides, spin-degenerated systems and magnetic vortices
DESCRIPTION:\nLPMS, CY Cergy Paris Université, Cergy-Pontoise, FranceUniversité Paris-Saclay, CEA, CNRS, LIDYL, Gif-sur-Yvette, France\n\n\n\nLight-matter interaction comprehends a number of fundamental processes at the core of most condensedmatter physics studies, where each time one measures some of the various properties (position, angularmomentum, energy, etc.) of photons, electrons and nuclei. While experimental challenging, it is of greatimportance to combine different degrees of freedom, in order to have a better insight of the particularprocess under examination and at the same time to exploit it as an investigation technique. In thisseminar, I will present three case studies with the common thread of combining different degrees offreedom in spectroscopic techniques in the extreme ultraviolet (XUV) range, with the aim of betterunderstanding the physical processes, and to extract qualitatively new type of information.\n\n\n\nIn photoemission, the spin polarization of the photoelectrons from spin-degenerate states andthe emission time delay in the attosecond domain are both linked to the phase term of thetransition matrix elements. I will present how to indirectly access the attosecond time scale froma measurement of the spin polarization as a function of electron binding energy [1].\n\n\n\n Alternatively, it is possible to directly access the time information in the photoemission processthrough a XUV pump – IR probe interferometer scheme. In this case, one probes the collectivedeexcitation process in the femtosecond domain. I will present a setup that allows to performangle-resolved photoemission spectrscopy (ARPES) with combined spin and time resolution (ST-ARPES), thus giving access not only to the charge but also to the spin dynamics. I will presentexperimental results on the transition metal dichalcogenide WTe2 [2], a precursor of Weyl type-IIsemimetal topological phase.\n\n\n\nIn addition to the spin angular momentum (SAM) associated to the circular polarization of a lightwave, a photon can carry also orbital angular momentum (OAM), corresponding to a helicoidalwavefront of light instead of a plane wave. While SAM of light is extensively used for dichroicstudies, this new OAM degree of freedom has been much less exploited. I will present the classicalelectromagnetic theory for the case of reflection of light carrying OAM by a non-uniform magneticmaterial, leading to a differential scattering associated to a so-called magnetic helicoidaldichroism (MHD) [3]. It is found that MHD gives information about the overall topology of themagnetic structure. I will also present the first experimental observation of MHD measured at theFERMI free electron laser on a permalloy magnetic vortex at the Fe 3p resonance [4]. Theexperimental results agree with the theoretical predictions, setting the ground for scan-freeinvestigations of ultrafast dynamics of magnetic structures with MHD.References:[1] M. Fanciulli et al., Physical Review Letters 118, 067402 (2017)[2] M. Fanciulli et al., Physical Review Research 2, 013261 (2020)[3] M. Fanciulli et al., Physical Review A 103, 013501 (2021)[4] M. Fanciulli et al., Physical Review Letters 128, 077401 (2022)\n
URL:https://www.lps.u-psud.fr/en/events/mauro-fanciulli-spin-orbit-and-time-resolved-spectroscopieson-transition-metal-dichalcogenides-spin-degenerated-systems-and-magnetic-vortices/
CATEGORIES:Seminar SMQ,Seminars
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