Condensed-Matter Physics & Materials Science Seminar

Photoemission is one of the most striking experimental techniques to probe the electronic structure of solids. Being a surface-sensitive probe it can particularly reveal features induced by electron-phonon coupling (EPC) which is often enhanced at surfaces. A prominent example in this respect is the hydrogen covered tungsten surface, where EPC has been found responsible for a splitting of one of the surface bands [1,2]. From the theoretical side, the Greens function approach can be employed to study such manybody effects. It will be shown that the self-consistent solution of the complex Dyson equation for the electron-phonon problem is needed to reveal such quasiparticle (QP) bands. To this extent, we have generalized a method proposed by Engelsberg and Schrieffer [3] for the Einstein model at T=0. While the basic features can be studied already in the Einstein model, the approach is much more powerful by being combined with first-principles results for the electronic and vibrational structure and extended to finite temperatures. Applying this procedure to H@W(110), the measured spin-polarized surface band splitting [1,2] can indeed be traced back to different QP states induced by EPC. Despite the breakdown of the single QP picture, the spectral functions are very well represented by the predicted multiple QP structure [4], with each of the QP states possessing a well defined energy and lifetime.
[1] E. Rotenberg et al., Phys. Rev. Lett. 84, 2925 (2000).
[2] E. Rotenberg et al., Phys. Rev. Lett. 89, 216802 (2002).
[3] S. Engelsberg, J. R. Schrieffer., Phys. Rev. 131, 993 (1963).
[4] A. Eiguren and C. Ambrosch-Draxl, Phys. Rev. Lett. 101, 036402 (2008).