464 research outputs found
Time-dependent screening of a positive charge distribution in metals: Excitons on an ultra-short time scale
Experiments determining the lifetime of excited electrons in crystalline
copper reveal states which cannot be interpreted as Bloch states [S. Ogawa {\it
et al.}, Phys. Rev. B {\bf 55}, 10869 (1997)]. In this article we propose a
model which explains these states as transient excitonic states in metals. The
physical background of transient excitons is the finite time a system needs to
react to an external perturbation, in other words, the time which is needed to
build up a polarization cloud. This process can be probed with modern
ultra-short laser pulses. We calculate the time-dependent density-response
function within the jellium model and for real Cu. From this knowledge it is
possible within linear response theory to calculate the time needed to screen a
positive charge distribution and -- on top of this -- to determine excitonic
binding energies. Our results lead to the interpretation of the experimentally
detected states as transient excitonic states.Comment: 24 pages, 9 figures, to appear in Phys. Rev. B, Nov. 15, 2000, issue
2
Plasmon Lifetime in K: A Case Study of Correlated Electrons in Solids Amenable to Ab Initio Theory
On the basis of a new ab initio, all-electron response scheme, formulated
within time-dependent density-functional theory, we solve the puzzle posed by
the anomalous dispersion of the plasmon linewidth in K. The key damping
mechanism is shown to be decay into particle-hole pairs involving empty states
of d-symmetry. While the effect of many-particle correlations is small, the
correlations built into the "final-state" -d-bands play an important, and
novel, role ---which is related to the phase-space complexity associated with
these flat bands. Our case study of plasmon lifetime in K illustrates the
importance of ab initio paradigms for the study of excitations in
correlated-electron systems.Comment: 12 pages, 4 figures, for html browsing see http://web.utk.edu/~weik
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The role of occupied d states in the relaxation of hot electrons in Au
We present first-principles calculations of electron-electron scattering
rates of low-energy electrons in Au. Our full band-structure calculations
indicate that a major contribution from occupied d states participating in the
screening of electron-electron interactions yields lifetimes of electrons in Au
with energies of above the Fermi level that are larger than
those of electrons in a free-electron gas by a factor of . This
prediction is in agreement with a recent experimental study of ultrafast
electron dynamics in Au(111) films (J. Cao {\it et al}, Phys. Rev. B {\bf 58},
10948 (1998)), where electron transport has been shown to play a minor role in
the measured lifetimes of hot electrons in this material.Comment: 4 pages, 2 figures, to appear in Phys. Rev.
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