5 research outputs found
Aharonov-Bohm effect in circular carbon nanotubes
We study the interference of interacting electrons in toroidal single-wall
carbon nanotubes coupled to metallic electrodes by tunnel junctions. The dc
conductance shows resonant features as a function of the gate voltage and the
magnetic field. The conductance pattern is determined by the interaction
parameter, which in turn can be cross-checked against the exponents governing
the transport at high temperatures. The coordinate dependence of the
conductance reflects electron correlations in one-dimensional space.Comment: 2 pages, contributed paper to LT-22, style file phbauth.cls is
include
Breakdown of the perturbative renormalization group at certain quantum critical points
It is shown that the presence of multiple time scales at a quantum critical
point can lead to a breakdown of the loop expansion for critical exponents,
since coefficients in the expansion diverge. Consequently, results obtained
from finite-order perturbative renormalization-group treatments may be not be
an approximation in any sense to the true asymptotic critical behavior. This
problem manifests itself as a non-renormalizable field theory, or,
equivalently, as the presence of a dangerous irrelevant variable. The quantum
ferromagnetic transition in disordered metals provides an example.Comment: 4pp, 1 eps fi
Tricritical behavior in itinerant quantum ferromagnets
It is shown that the peculiar features observed in the low-temperature phase
diagrams of ZrZn_2, UGe_2, and MnSi can be understood in terms of a simple
mean-field theory. The nature of the ferromagnetic transition changes from
second order to first order at a tricritical point, and in a small external
magnetic field surfaces of first-order transitions emerge which terminate in
quantum critical points. This field dependence of the phase diagram follows
directly from the existence of the tricritical point. The quantum critical
behavior in a nonzero field is calculated exactly.Comment: 4pp., 4 eps figure
Tunneling Density of States of the Interacting Two-Dimensional Electron Gas
We investigate the influence of electron--electron interactions on the
density of states of a ballistic two--dimensional electron gas. The density of
states is determined nonperturbatively by means of path integral techniques
allowing for reliable results near the Fermi surface, where perturbation theory
breaks down. We find that the density of states is suppressed at the Fermi
level to a finite value. This suppression factor grows with decreasing electron
density and is weakened by the presence of gates.Comment: 4 pages, 2 figures; slightly shortened version published in PR
Coulomb Blockade of Tunneling between Disordered Conductors
We determine the zero-bias anomaly of the conductance of tunnel junctions by
an approach unifying the conventional Coulomb blockade theory for ultrasmall
junctions with the diffusive anomalies in disordered conductors. Both,
electron-electron interactions within the electrodes and electron-hole
interactions between the electrodes are taken into account nonperturbatively.
Explicit results are given for one- and two-dimensional junctions, and the
crossover to ultrasmall junctions is discussed.Comment: 4 pages, 1 figure. Final version published in Phys. Rev. Let