Coulomb Drag and Spin Coulomb Drag in the presence of Spin-orbit Coupling

Employing diagrammatic perturbation theory, we calculate the (charge) Coulomb drag resistivity $\rho_D$ and spin Coulomb drag resistivity $\rho_{\uparrow\downarrow}$ in the presence of Rashba spin-orbit coupling. Analytical expressions for $\rho_D$ and $\rho_{\uparrow\downarrow}$ are derived, and it is found that spin-orbit interaction produces a small enhancement to $\rho_D$ and $\rho_{\uparrow\downarrow}$ in the ballistic regime while $\rho_D$ is unchanged in the diffusive regime. This enhancement in the ballistic regime is attributed to the enhancement of the nonlinear susceptibility (i.e. current produced through the rectification of the thermal electric potential fluctuations in the passive layer) while the lack of enhancement in the diffusive regime is due to the suppression by disorder.Comment: 8 pages, 2 figure

Exchange-Rate Systems and Interest-Rate Behaviour: The Experience of Hong Kong and Singapore

The Currency Board System in Hong Kong and the monitoring band system in Singapore are important benchmarks for two different exchange-rate systems. In this paper we consider the implications of the two exchange-rate systems on the interest-rate behaviour of the two economies. We examine the domestic-US interest differentials under the two exchange-rate regimes during the Asian Financial Crisis as well as the pre- and post-crisis periods. Using a bivariate generalized autoregressive conditional heteroscedasticity model, we also investigate whether there is any change in the correlation between the domestic and US interest rates due to the Asian Financial Crisis.

Energy Relaxation of Hot Dirac Fermions in Graphene

We develop a theory for the energy relaxation of hot Dirac fermions in graphene. We obtain a generic expression for the energy relaxation rate due to electron-phonon interaction and calculate the power loss due to both optical and acoustic phonon emission as a function of electron temperature $T_{\mathrm{e}}$ and density $n$. We find an intrinsic power loss weakly dependent on carrier density and non-vanishing at the Dirac point $n = 0$, originating from interband electron-optical phonon scattering by the intrinsic electrons in the graphene valence band. We obtain the total power loss per carrier $\sim 10^{-12} - 10^{-7} \mathrm{W}$ within the range of electron temperatures $\sim 20 - 1000 \mathrm{K}$. We find optical (acoustic) phonon emission to dominate the energy loss for $T_{\mathrm{e}} > (<) 200-300 \mathrm{K}$ in the density range $n = 10^{11}-10^{13} \mathrm{cm}^{-2}$.Comment: 5 page

Ballistic Hot Electron Transport in Graphene

We theoretically study the inelastic scattering rate and the carrier mean free path for energetic hot electrons in graphene, including both electron-electron and electron-phonon interactions. Taking account of optical phonon emission and electron-electron scattering, we find that the inelastic scattering time $\tau \sim 10^{-2}-10^{-1} \mathrm{ps}$ and the mean free path $l \sim 10-10^2 \mathrm{nm}$ for electron densities $n = 10^{12}-10^{13} \mathrm{cm}^{-2}$. In particular, we find that the mean free path exhibits a finite jump at the phonon energy $200 \mathrm{meV}$ due to electron-phonon interaction. Our results are directly applicable to device structures where ballistic transport is relevant with inelastic scattering dominating over elastic scattering.Comment: 4 page