Abstract by: Daniel Sánchez-Portal

Understanding Charge-Transfer Dynamics at Interfaces from First-Principles Calculations

In this talk I will present a short review of some of our efforts to understand ultrafast charge-transfer dynamics at interfaces in connection to pump-probe two-photon photoemission and core-hole clock spectroscopy experiments [1,2,3]. In particular, I will spend most of my time describing our collaboration with the group of Prof. Gian-Paolo Brivio to compute charge-transfer times using Green’s function techniques in combination with density funtional theory calculations at interfaces relevant for photovoltaics. In particular, we studied in detail the case of isonicotinic acid on rutile (110), where we analyzed carefully the effect of core excitations and structural fluctuations at finite temperature (see the Figure below) on the energy positions of the molecular levels and their elastic lifetimes [4,5].

More recently we have investigated the effect of the spin orientation in the charge transfer dynamics on ferromagnetic metal substrates, focusing on the case of core-excited Ar on Co(001) and Fe(110). For these systems, recent core-hole-clock measurements [1] of the lifetime of the 4s level of core-excited Ar have shown a clear dependence on the spin of the excited electron. Minority electrons in the Ar* 4s state decay significantly faster than majority electrons. Our calculations agree with the observed behavior and allow analyzing in detail the origin of this phenomenon [7]. The key ingredient behind the observed behavior is the spin dependence of the bandstructure of the substrate and, in particular, the very different position of the Ar* 4s level within the projected band gap appearing around Gamma in the dispersive bands of Co(001) and Fe(110) for both spin channels.

[1] A. Föhlisch, P. Feulner, F. Hennies, A. Fink, D. Menzel, D. Sánchez-Portal, P. M. Echenique, W. Wurth, Nature 436, 373 (2005)

[2] D. Sánchez-Portal, Prog. Surf. Sci. 82, 313 (2007)

[3] D. Sánchez-Portal, D. Menzel, P. M. Echenique, Phys. Rev. B 76, 235406 (2007)

[4] G. Fratesi, C. Motta, M. I. Trioni, G.-P. Brivio, D. Sánchez-Portal, J. Phys. Chem. 118, 8775 (2014)

[5] M. Müller, D. Sánchez-Portal, H. Lin, G.-P. Brivio, D. A. Selloni and G. Fratesi, J. Phys. Chem. C 122, 7575-7585 (2018)

[6] F. Blobner, et al., Phys. Rev. Lett. 112, 086801 (2014)

[7] M. Müller, P. M. Echenique and D. Sánchez-Portal, in preparation