On the effects of irrelevant boundary scaling operators

We investigate consequences of adding irrelevant (or less relevant) boundary operators to a (1+1)-dimensional field theory, using the Ising and the boundary sine-Gordon model as examples. In the integrable case, irrelevant perturbations are shown to multiply reflection matrices by CDD factors: the low-energy behavior is not changed, while various high-energy behaviors are possible, including ``roaming'' RG trajectories. In the non-integrable case, a Monte Carlo study shows that the IR behavior is again generically unchanged, provided scaling variables are appropriately renormalized.Comment: 4 Pages RevTeX, 3 figures (eps files

Doping- and size-dependent suppression of tunneling in carbon nanotubes

We study the effect of doping in the suppression of tunneling observed in multi-walled nanotubes, incorporating as well the influence of the finite dimensions of the system. A scaling approach allows us to encompass the different values of the critical exponent $\alpha$ measured for the tunneling density of states in carbon nanotubes. We predict that further reduction of $\alpha$ should be observed in multi-walled nanotubes with a sizeable amount of doping. In the case of nanotubes with a very large radius, we find a pronounced crossover between a high-energy regime with persistent quasiparticles and a low-energy regime with the properties of a one-dimensional conductor.Comment: 4 pages, 2 figures, LaTeX file, pacs: 71.10.Pm, 71.20.Tx, 72.80.R

Coulomb Charging at Large Conduction

We discuss the suppression of Coulomb charging effects on a small metallic island coupled to an electrode by a tunnel junction. At high temperatures the quantum corrections to the classical charging energy $E_c=e^2/2C$, where $C$ is the island capacitance, are evaluated. At low temperatures the large quantum fluctuations of the island charge cause a strong reduction of the effective $E_c$ which is determined explicitly in the limit of a large tunneling conductance.Comment: 4 page

Coulomb drag shot noise in coupled Luttinger liquids

Coulomb drag shot noise has been studied theoretically for 1D interacting electron systems, which are realized e.g. in single-wall nanotubes. We show that under adiabatic coupling to external leads, the Coulomb drag shot noise of two coupled or crossed nanotubes contains surprising effects, in particular a complete locking of the shot noise in the tubes. In contrast to Coulomb drag of the average current, the noise locking is based on a symmetry of the underlying Hamiltonian and is not limited to asymptotically small energy scales.Comment: 4 pages Revtex, accepted for publication in PR

Current bistability and hysteresis in strongly correlated quantum wires

Nonequilibrium transport properties are determined exactly for an adiabatically connected single channel quantum wire containing one impurity. Employing the Luttinger liquid model with interaction parameter $g$, for very strong interactions g\lapx 0.2, and sufficiently low temperatures, we find an S-shaped current-voltage relation. The unstable branch with negative differential conductance gives rise to current oscillations and hysteretic effects. These non perturbative and non linear features appear only out of equilibrium.Comment: 4 pages, 1 figur

Electroneutrality and the Friedel sum rule in a Luttinger liquid

Screening in one-dimensional metals is studied for arbitrary electron-electron interactions. It is shown that for finite-range interactions (Luttinger liquid) electroneutrality is violated. This apparent inconsistency can be traced to the presence of external screening gates responsible for the effectively short-ranged Coulomb interactions. We also draw attention to the breakdown of linear screening for wavevectors close to 2 K_f.Comment: 4 pages REVTeX, incl one figure, to appear in Phys.Rev.Let

Charging effects in quantum wires

We investigate the role of charging effects in a voltage-biased quantum wire. Both the finite range of the Coulomb interaction and the long-ranged nature of the Friedel oscillation imply a finite capacitance, leading to a charging energy. While observable Coulomb blockade effects are absent for a single impurity, they are crucial if islands are present. For a double barrier, we give the resonance condition, fully taking into account the charging of the island.Comment: 6 Pages RevTeX, no figures, Phys. Rev. B (in press

Form-factors computation of Friedel oscillations in Luttinger liquids

We show how to analytically determine for $g\leq 1/2$ the "Friedel oscillations" of charge density by a single impurity in a 1D Luttinger liquid of spinless electrons.Comment: Revtex, epsf, 4pgs, 2fig

Current-induced non-adiabatic spin torques and domain wall motion with spin relaxation in a ferromagnetic metallic wire

Within the s-d model description, we derive the current-driven spin torque in a ferromagnet, taking explicitly into account a spin-relaxing Caldeira-Leggett bath coupling to the s-electrons. We derive Bloch-Redfield equations of motion for the s-electron spin dynamics, and formulate a systematic gradient expansion to obtain non-adiabatic (higher-order) corrections to the well-known adiabatic (first-order) spin torque. We provide simple analytical expressions for the second-order spin torque. The theory is applied to current-driven domain wall motion. Second-order contributions imply a deformation of a transverse tail-to-tail domain wall. The wall center still moves with a constant velocity that now depends on the spin-polarized current in a non-trivial manner.Comment: Phys. Rev. B, in press, replaced with published versio