28 research outputs found
Ultrafast quasiparticle relaxation dynamics in normal metals and heavy fermion materials
We present a detailed theoretical study of the ultrafast quasiparticle
relaxation dynamics observed in normal metals and heavy fermion materials with
femtosecond time-resolved optical pump-probe spectroscopy. For normal metals, a
nonthermal electron distribution gives rise to a temperature (T) independent
electron-phonon relaxation time at low temperatures, in contrast to the
T^{-3}-divergent behavior predicted by the two-temperature model. For heavy
fermion compounds, we find that the blocking of electron-phonon scattering for
heavy electrons within the density-of-states peak near the Fermi energy is
crucial to explain the rapid increase of the electron-phonon relaxation time
below the Kondo temperature. We propose the hypothesis that the slower Fermi
velocity compared to the sound velocity provides a natural blocking mechanism
due to energy and momentum conservation laws.Comment: 10 pages, 11 figure
Size-dependent Correlation Effects in Ultrafast Optical Dynamics of Metal Nanoparticles
We study the role of collective surface excitations in the electron
relaxation in small metal particles. We show that the dynamically screened
electron-electron interaction in a nanoparticle contains a size-dependent
correction induced by the surface. This leads to new channels of quasiparticle
scattering accompanied by the emission of surface collective excitations. We
calculate the energy and temperature dependence of the corresponding rates,
which depend strongly on the nanoparticle size. We show that the
surface-plasmon-mediated scattering rate of a conduction electron increases
with energy, in contrast to that mediated by a bulk plasmon. In noble-metal
particles, we find that the dipole collective excitations (surface plasmons)
mediate a resonant scattering of d-holes to the conduction band. We study the
role of the latter effect in the ultrafast optical dynamics of small
nanoparticles and show that, with decreasing nanoparticle size, it leads to a
drastic change in the differential absorption lineshape and a strong frequency
dependence of the relaxation near the surface plasmon resonance. The
experimental implications of our results in ultrafast pump-probe spectroscopy
are also discussed.Comment: 29 pages including 6 figure
Effect of a nonthermal electron distribution on the electron-phonon energy relaxation process in noble metals
The capacitive origin of the picosecond electrical transients detected by a photoconductively gated scanning tunneling microscope
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Effect of a Nonthermal Electron-Distribution on the Electron-Phonon Energy Relaxation Process in Noble-Metals
Effect of a Nonthermal Electron-Distribution on the Electron-Phonon Energy Relaxation Process in Noble-Metals
Femtosecond spectroscopy of electron-electron and electron-phonon energy relaxation in Ag and Au
Modulated Photodetection with Semiconductor Tips in a Scanning Tunneling Microscope
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