Transport and Coulomb drag for two interacting carbon nanotubes

We study nonlinear transport for two coupled one-dimensional quantum wires or carbon nanotubes described by Luttinger liquid theory. Transport properties are shown to crucially depend on the contact length $L_c$. For a special interaction strength, the problem can be solved analytically for arbitrary $L_c$. For point-like contacts and strong interactions, a qualitatively different picture compared to a Fermi liquid emerges, characterized by zero-bias anomalies and strong dependence on the applied cross voltage. In addition, pronounced Coulomb drag phenomena are important for extended contacts.Comment: 9 pages, 7 figures (eps files

Luttinger liquid behavior in single wall nanotubes

Transport properties of metallic single-wall nanotubes are examined based on the Luttinger liquid theory. Focusing on a nanotube transistor setup, the linear conductance is computed from the Kubo formula using perturbation theory in the lead-tube tunnel conductances. For sufficiently long nanotubes and high temperature, phonon backscattering should lead to an anomalous temperature dependence of the resistivity.Comment: 5 pages, to appear in IWEPNM99 proceedings 1999, incl 2 figure

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

Impurity effects in few-electron quantum dots: Incipient Wigner molecule regime

Numerically exact path-integral Monte Carlo data are presented for $N\leq 10$ strongly interacting electrons confined in a 2D parabolic quantum dot, including a defect to break rotational symmetry. Low densities are studied, where an incipient Wigner molecule forms. A single impurity is found to cause drastic effects: (1) The standard shell-filling sequence with magic numbers $N=4,6,9$, corresponding to peaks in the addition energy $\Delta(N)$, is destroyed, with a new peak at N=8, (2) spin gaps decrease, (3) for N=8, sub-Hund's rule spin S=0 is induced, and (4) spatial ordering of the electrons becomes rather sensitive to spin. We also comment on the recently observed bunching phenomenon.Comment: 7 pages, 1 table, 4 figures, accepted for publication in Europhysics Letter

Multilevel blocking Monte Carlo simulations for quantum dots

This article provides an introduction to the ideas behind the multilevel blocking (MLB) approach to the fermion sign problem in path-integral Monte Carlo simulations, and also gives a detailed discussion of MLB results for quantum dots. MLB can turn the exponential severity of the sign problem into an algebraic one, thereby enabling numerically exact studies of otherwise inaccessible systems. Low-temperature simulation results for up to eight strongly correlated electrons in a parabolic 2D quantum dot are presented.Comment: 10 Pages, includes 4 figures and mprocl.st