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Quasiparticle lifetimes in metallic quantum-well nanostructures

Nature Physics volume 6, pages 782–785 (2010)Cite this article

Abstract

Quasiparticle lifetimes in metals as described by Fermi-liquid theory1 are essential in surface chemistry2 and determine the mean free path of hot carriers3. Relaxation of hot electrons is governed by inelastic electron–electron scattering, which occurs on femtosecond timescales owing to the large scattering phase space competing with screening effects4. Such lifetimes are widely studied by time-resolved two-photon photoemission5,6, which led to understanding of electronic decay at surfaces6,7,8. In contrast, quasiparticle lifetimes of metal bulk5,9,10,11,12 and films11,13,14,15 are not well understood because electronic transport10,16,17 leads to experimental lifetimes shorter than expected theoretically13,15,18. Here, we lift this discrepancy by investigating Pb quantum-well structures on Si(111), a two-dimensional model system19,20,21,22,23,24,25,26,27,28,29. For electronic states confined to the film by the Si bandgap we find quantitative agreement with Fermi-liquid theory and ab initio calculations4,7 for bulk Pb, which we attribute to efficient screening. For states resonant with Si bands, extra decay channels open for electron transfer to Si, resulting in lifetimes shorter than expected for bulk. Thereby we demonstrate that for understanding electronic decay in nanostructures coupling to the environment is essential, and that even for electron confinement to a few ångströms Fermi-liquid theory for bulk can remain valid.

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Figure 1: Quantized band structure of Pb/Si(111) for the occupied and unoccupied density of states at the  point observed by photoemission.
Figure 2: Decay of the transient quasiparticle population in the luQWS for various N.
Figure 3: Lifetime of the luQWS as a function of Pb thickness.
Figure 4: Comparison of the measured quasiparticle lifetimes with theoretical results from FLT and the G W approximation.

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Acknowledgements

We thank C. Brun for discussions and acknowledge support from and discussions with M. Wolf. This work has been funded by the Deutsche Forschungsgemeinschaft through BO 1823/2 and by the Ministerio de Ciencia y Tecnologia (grant FIS2007-66711-C02-01). P.S.K. acknowledges support by the International Max-Planck Research School ‘Complex Surfaces in Material Science’.

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Authors and Affiliations

  1. Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin-Dahlem, Germany

    Patrick S. Kirchmann, Laurenz Rettig & Uwe Bovensiepen

  2. Stanford Institute for Material and Energy Science, 476 Lomita Mall, Stanford, 94305, California, USA

    Patrick S. Kirchmann

  3. Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal, 4, 20018 San Sebastian/Donostia, Basque Country, Spain

    Xabier Zubizarreta, Vyacheslav M. Silkin & Evgueni V. Chulkov

  4. Departamento de Física de Materiales, Facultad de Ciencias Químicas, UPV/EHU, Apdo. 1072, 20080 San Sebastián, Basque Country, Spain

    Xabier Zubizarreta, Vyacheslav M. Silkin & Evgueni V. Chulkov

  5. IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Basque Country, Spain

    Vyacheslav M. Silkin

  6. Centro de Física de Materiales CFM - Materials Physics Center MPC, Centro Mixto CSIC-UPV/EHU, Edificio Korta, Avenida de Tolosa 72, 20018 San Sebastián, Spain

    Evgueni V. Chulkov

  7. Fakultät für Physik, Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany

    Uwe Bovensiepen

Authors
  1. Patrick S. Kirchmann
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  2. Laurenz Rettig
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  6. Uwe Bovensiepen
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Contributions

P.S.K. and L.R. carried out the experiments and analysed the data; U.B. designed and coordinated the experiment; X.Z. and V.M.S. carried out the calculations; P.S.K., U.B., and E.V.C. wrote the paper; all authors commented on the manuscript.

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Correspondence to Uwe Bovensiepen.

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The authors declare no competing financial interests.

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Kirchmann, P., Rettig, L., Zubizarreta, X. et al. Quasiparticle lifetimes in metallic quantum-well nanostructures. Nature Phys 6, 782–785 (2010). https://doi.org/10.1038/nphys1735

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