Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 55: Time-resolved spectroscopies II
O 55.3: Talk
Thursday, March 26, 2009, 15:30–15:45, SCH A315
The role of exchange scattering in the spin-dependent lifetime of hot electrons — •Andreas Goris1,2, Ilja Panzer1,2, Kristian Döbrich1, Martin Pickel1, Anke B. Schmidt3, Markus Donath3, and Martin Weinelt1,2 — 1Max-Born-Institut, 12489 Berlin — 2Freie Universität Berlin, 14195 Berlin — 3Physikalisches Institut, Universität Münster, 48149 Münster
We have identified a Δ1 surface resonance of minority character on cobalt thin films on Cu(001) at 0.45 eV below the Fermi level in spin-resolved photoemission and two-photon photoemission (2PPE) [1]. With a laser pulse (hν = 1.5 eV) we excite electrons above the Fermi level and create photoholes in the surface resonance. A second UV laser pulse is used to probe lifetimes and spin-polarization of the excited electrons. While the hot electron lifetime shows only weak spin dependence (τ↑=30 fs; τ↓=22 fs at E− EF = 0.25 eV), we find a long-living tail with predominantly majority character for energies up to 0.45 eV above EF. By quenching the minority surface resonance with oxygen adsorption, the long-living tail of majority electrons vanishes. This strongly suggests that exchange scattering dominates hot electron decay and leads to the discrepancy between measured and calculated hot electron lifetimes [2,3]: the minority photohole is filled by a minority electron and in exchange a majority electron is excited above EF, thereby adapting τ↑ and τ↓ .
[1] A. B. Schmidt et. al., J. Phys. D 41 No 16, 164003 (2008)
[2] Aeschlimann et al., Phys. Rev. Lett. 79, 5158 (1997)
[3] Zhukov et al., Phys. Rev. Lett. 93, 096401 (2004)