Abstract
We investigate the spectroscopy and photoinduced electron dynamics within the conduction band of reduced rutile surface by multiphoton photoemission spectroscopy with wavelength tunable ultrafast laser pulse excitation. Tuning the photon excitation energy between 2.9 and 4.6 eV reveals a nearly degenerate pair of new unoccupied states located at and eV above the Fermi level, which can be analyzed through the polarization and sample azimuthal orientation dependence of the spectra. Based on the calculated electronic structure and optical transition moments, as well as related spectroscopic evidence, we assign these resonances to transitions between bands of nominally and symmetry, which are split by crystal field. The initial states for the optical transition are the reduced states of symmetry populated by formation oxygen vacancy defects, which exist within the band gap of . Furthermore, we studied the electron dynamics within the conduction band of by three-dimensional time-resolved pump-probe interferometric measurements. The spectroscopic and time-resolved studies reveal competition between 2PP and 3PP processes where the transitions in the 2PP process saturate, and are overtaken by the 3PP process initiated by the band-gap excitation from the valence band of .
1 More- Received 21 December 2014
- Revised 4 April 2015
DOI:https://doi.org/10.1103/PhysRevB.91.155429
©2015 American Physical Society