|approved||osi11_petek_ext.pdf||2015-04-05 21:55:11||Hrvoje Petek|
Author: Hrvoje Petek
Requested Type: Pre-Selected Invited
Submitted: 2015-03-13 15:16:24
University of Pittsburgh
3941 O'Hara St.
Pittsburgh, PA 15260
We study the interaction of light with noble metals by coherent multi-dimensional multi-photon photoemission (mPP) spectroscopy. By employing single color, broadly tunable <15 fs pulse excitation and energy vs. momentum photoelectron imaging, we record movies of the photoexcitation pathways in metals. We identify features in the mPP spectra, which cannot be attributed to single particle excitations among the well-known surface and bulk bands of Cu and Ag. In the case of 3PP form Ag(111), a nondispersive feature, which dominates the spectra, appears when the laser is tuned near the resonance from the Shockley surface state (SS) and the image potential state. We attribute this spectrum to a transient exciton corresponding to electron excited from the SS interacting through the Coulomb interaction with the created hole on the timescale of screening. Interferometric time-resolved photoemission movies of 3PP identify the coherent pathways and timescales for mPP via the transient exciton resonance. In the case of Cu(111) surface we see no evidence for the transient exciton. Rather, at excitation wavelengths approaching the d- to sp-band threshold we see a multiplication of the SS band, which we attribute to polaritonic local fields associated with the slowly dephasing d- to sp-band transitions.
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