Scattering rate

Abstract: Coupling between electrons and phonons (lattice vibrations) drives the formation of the electron pairs responsible for conventional superconductivity. The lack of direct evidence for electron-phonon coupling in the electron dynamics of the high-transition-temperature superconductors has driven an intensive search for an alternative mechanism. A coupling of an electron with a phonon would result in an abrupt change of its velocity and scattering rate near the phonon energy. Here we use angle-resolved photoemission spectroscopy to probe electron dynamics-velocity and scattering rate-for three different families of copper oxide superconductors. We see in all of these materials an abrupt change of electron velocity at 50-80 meV, which we cannot explain by any known process other than to invoke coupling with the phonons associated with the movement of the oxygen atoms. This suggests that electron-phonon coupling strongly influences the electron dynamics in the high-temperature superconductors, and must therefore be included in any microscopic theory of superconductivity.

Abstract: The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of 1-20x10(3) cm2/V sec. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from 2-15x10(11) cm(-2). In the low carrier density limit, the conductivity exhibits values in the range of 2-12e2/h, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short-range disorder whereas low mobility samples are dominated by long-range scatterers.

Abstract: The energy-dependent rate for inelastic scattering of electrons by production of electron-hole pairs is computed by first-order perturbation theory for silicon using a screened Coulomb interaction with a frequency- and momentum-dependent dielectric function calculated for silicon in the random-phase approximation. The threshold for momentum-conserving pair creation is found to be very close to that determined by energy conservation alone. This follows from the silicon band structure. The absolute scattering rate is close to that obtained experimentally by Bartelink, Moll, and Meyer. Pair production dominates the scattering rate for electrons of energy greater than 6.5 eV above the valence-band maximum. For electrons between 4 and 6.5 eV the scattering rate is dominated by phonon scattering, but energy loss is dominated by pair scattering. Below 4 eV phonon processes dominate inelastic processes as well. The momentum space integrals for pair-creation scattering are performed by a Monte Carlo method. It is found that the calculations with momentum conservation can be reproduced surprisingly well by a simple "random-k" approximation, which effectively ignores momentum conservation. This leads to a very simple expression for pair scattering in the form of a two-dimensional energy fold over one-electron state-density functions, a result first obtained by Berglund and Spicer. This simple form facilitates the calculation tremendously and should make calculations for other materials very simple if the state-density function is known. Using this "random-k" method, the scattering rate for primary holes is obtained and found to be almost identical with that for primary electrons of comparable energy. The secondary-particle energy distribution functions are also determined for primary holes and electrons. One-electron state-density structure is prominent in these distributions.

Abstract: Many exotic compounds, such as cuprate superconductors and heavy fermion materials, exhibit a linear in temperature (T) resistivity, the origin of which is not well understood. We found that the resistivity of the quantum critical metal Sr(3)Ru(2)O(7) is also T-linear at the critical magnetic field of 7.9 T. Using the precise existing data for the Fermi surface topography and quasiparticle velocities of Sr(3)Ru(2)O(7), we show that in the region of the T-linear resistivity, the scattering rate per kelvin is well approximated by the ratio of the Boltzmann constant to the Planck constant divided by 2π. Extending the analysis to a number of other materials reveals similar results in the T-linear region, in spite of large differences in the microscopic origins of the scattering.

Abstract: The surface plasmon damping induced by high excitation of the electron gas is studied in femtosecond pump-and-probe experiments on gold colloids embedded in a sol-gel matrix. Optical excitation of single-particle interband transitions leads to a pronounced broadening of the surface plasmon line. A similar behavior is observed for resonant excitation of the surface plasmon. This broadening is the dominant optical nonlinearity of the system, and reflects the excitation-induced damping of the surface plasmon resonance. The time evolution of the damping rate follows that of the electronic scattering rate.