engleski

Ultrafast dynamics of the Pb/Si(557) nanowire system: analysis of many-body interactions in the time domain

Very good candidates to study the exotic physics of quasi 1D systems are self-assembled atomic wires. Particularly attractive are metallic wires adsorbed on semiconducting surfaces which are not only geometrically strongly anisotropic, but also exhibit quasi-1D Fermi surfaces. In metallic wires, rather strong correlation effects are expected due to the reduction of electrostatic screening. However, the correlations are modified in quasi-1D electron systems owing to the coupling to the environment. Interactions wire to wire and wire to substrate should also manifest themselves in the electronic structure and in an anisotropic electronic interaction and relaxation dynamics after photoexcitation. As a prototypical system we studied the Pb/Si(557) nanowire system with the intention to explore the impact of structural and electronic band anisotropy to the ultrafast hot electron decay dynamics. To investigate elementary and microscopic interactions responsible for the population decay of optically excited electrons as a function of electron momentum we used femtosecond time- and angle-resolved two photon photoemission spectroscopy (2PPE). Two bands in the unoccupied electronic band structure are identified for which the dynamics in various points of the in-plane k-space was studied. We find indications of a momentum dependent population probability, but at present the band structure effects cannot be excluded. As already reported, the electrical conductivity in the system switches from 2D to 1D behaviour upon crossing the critical temperature due to the temperature dependent structural transition. This structural instability opens the opportunity to study different aspects, for example temperaturedependent dynamics or the optically driven insulator-metal transition in the future.

ultrafast dynamics; time domain

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