6 research outputs found
Nodal Gap in Fe-Based Layered Superconductor LaO_0.9F_{0.1-delta}FeAs Probed by Specific Heat Measurements
We report the specific heat measurements on the newly discovered Fe-based
layered superconductor LaO_0.9F_{0.1-delta}FeAs with the onset transition
temperature T_c \approx 28 K. A nonlinear magnetic field dependence of the
electronic specific heat coefficient gamma(H) has been found in the low
temperature limit, which is consistent with the prediction for a nodal
superconductor. The maximum gap value Delta_0 \approx 3.40.5 meV was
derived by analyzing gamma(H) based on the d-wave model. We also detected the
electronic specific heat difference between 9 T and 0 T in wide temperature
region, a specific heat anomaly can be clearly observed near T_c. The Debye
temperature of our sample was determined to be about 315.7 K. Our results
suggest an unconventional mechanism for this new superconductor.Comment: 4 pages, 4 figures,Corrected typo
Coulomb scattering lifetime of a two-dimensional electron gas
Motivated by a recent tunneling experiment in a double quantum-well system,
which reports an anomalously enhanced electronic scattering rate in a clean
two-dimensional electron gas, we calculate the inelastic quasiparticle lifetime
due to electron-electron interaction in a single loop dynamically screened
Coulomb interaction within the random-phase-approximation. We obtain excellent
quantitative agreement with the inelastic scattering rates in the tunneling
experiment without any adjustable parameter, finding that the reported large
( a factor of six) disagreement between theory and experiment arises from
quantitative errors in the existing theoretical work and from the off-shell
energy dependence of the electron self-energy.Comment: 11 pages, RevTex, figures included. Also available at
http://www-cmg.physics.umd.edu/~lzheng
Inelastic lifetimes of confined two-component electron systems in semiconductor quantum wire and quantum well structures
We calculate Coulomb scattering lifetimes of electrons in two-subband quantum
wires and in double-layer quantum wells by obtaining the quasiparticle
self-energy within the framework of the random-phase approximation for the
dynamical dielectric function. We show that, in contrast to a single-subband
quantum wire, the scattering rate in a two-subband quantum wire contains
contributions from both particle-hole excitations and plasmon excitations. For
double-layer quantum well structures, we examine individual contributions to
the scattering rate from quasiparticle as well as acoustic and optical plasmon
excitations at different electron densities and layer separations. We find that
the acoustic plasmon contribution in the two-component electron system does not
introduce any qualitatively new correction to the low energy inelastic
lifetime, and, in particular, does not produce the linear energy dependence of
carrier scattering rate as observed in the normal state of high-
superconductors.Comment: 16 pages, RevTeX, 7 figures. Also available at
http://www-cmg.physics.umd.edu/~lzheng