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O: Fachverband Oberflächenphysik
O 76: Ultrafast Electron and spin dynamics at interfaces III
O 76.1: Vortrag
Mittwoch, 14. März 2018, 17:30–17:45, MA 005
Coherent many-particle excitations in NiO ultrathin films — •Konrad Gillmeister1 and Wolf Widdra1,2 — 1Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany — 2Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany
Strong electronic correlation in NiO causes the appearance of a charge-transfer gap (CTG). Its lower and upper edges (Hubbard bands) are formed by Ni 3d electrons. In this contribution we focus on the electron dynamics after exciting electrons into the upper Hubbard band.
Using time-resolved two-photon photoemission spectroscopy (2PPE) on 1–20 monolayers (ML) NiO ultrathin films on Ag(001) we find that electrons decay within 15 fs across the CTG. However, there is a second long-living contribution to the 2PPE signal which is thickness- and temperature-dependent: periodic intensity modulations in the detected time-resolved signal near the vacuum cut-off with a lifetime of ∼350 fs are found for NiO film thicknesses beyond 5 ML and temperatures below 470 K for 10 ML (560 K for 20 ML). These oscillations are exlained by intra-gap states which are indirectly but coherently addressed by an instantaneous decay of excited electrons and which are subsequently probed. A simultaneous excitation of magnons is also discussed.