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 3.4$\pm$0.5 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 ($\geq$ 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-$T_c$ superconductors.Comment: 16 pages, RevTeX, 7 figures. Also available at http://www-cmg.physics.umd.edu/~lzheng