5,046 research outputs found
Magnetic confinement of massless Dirac fermions in graphene
Due to Klein tunneling, electrostatic potentials are unable to confine Dirac
electrons. We show that it is possible to confine massless Dirac fermions in a
monolayer graphene sheet by inhomogeneous magnetic fields. This allows one to
design mesoscopic structures in graphene by magnetic barriers, e.g. quantum
dots or quantum point contacts.Comment: 4 pages, 3 figures, version to appear in PR
Transport in Double-Crossed Luttinger Liquids
We study transport through two Luttinger liquids (one-dimensional electrons
interacting through a Coulomb repulsion in a metal) coupled together at {\it
two} points. External voltage biases are incorporated through boundary
conditions. We include density-density couplings as well as single-particle
hops at the contacts. For weak repulsive interactions, transport through the
wires remains undisturbed by the inter-wire couplings, which renormalise to
zero. For strong repulsive interactions, the inter-wire couplings become
strong. For symmetric barriers and no external voltage bias, a single gate
voltage is sufficient to tune for resonance transmission in both wires.
However, for asymmetric couplings or for finite external biases, the system is
insulating.Comment: Latex file, 11 pages, one eps figur
Bulk and boundary zero-bias anomaly in multi-wall carbon nanotubes
We compute the tunneling density of states of doped multi-wall nanotubes
including disorder and electron-electron interactions. A non-conventional
Coulomb blockade reflecting nonperturbative Altshuler-Aronov-Lee power-law
zero-bias anomalies is found, in accordance with recent experimental results.
The presence of a boundary implies a universal doubling of the boundary
exponent in the diffusive limit.Comment: 4 pages, to appear in PRL (revised version
Applying voltage sources to a Luttinger liquid with arbitrary transmission
The Landauer approach to transport in mesoscopic conductors has been
generalized to allow for strong electronic correlations in a single-channel
quantum wire. We describe in detail how to account for external voltage sources
in adiabatic contact with a quantum wire containing a backscatterer of
arbitrary strength. Assuming that the quantum wire is in the Luttinger liquid
state, voltage sources lead to radiative boundary conditions applied to the
displacement field employed in the bosonization scheme. We present the exact
solution of the transport problem for arbitrary backscattering strength at the
special Coulomb interaction parameter g=1/2.Comment: 9 pages REVTeX, incl 2 fig
Roadmap to Majorana surface codes
Surface codes offer a very promising avenue towards fault-tolerant quantum
computation. We argue that two-dimensional interacting networks of Majorana
bound states in topological superconductor/semiconductor heterostructures hold
several distinct advantages in that direction, both concerning the hardware
realization and the actual operation of the code. We here discuss how
topologically protected logical qubits in this Majorana surface code
architecture can be defined, initialized, manipulated, and read out. All
physical ingredients needed to implement these operations are routinely used in
topologically trivial quantum devices. In particular, we show that by means of
quantum interference terms in linear conductance measurements, composite
single-electron pumping protocols, and gate-tunable tunnel barriers, the full
set of quantum gates required for universal quantum computation can be
implemented.Comment: 23 pages, 8 figure
Paraconductivity in Carbon Nanotubes
We report the calculation of paraconductivity in carbon nanotubes above the
superconducting transition temperature. The complex behavior of
paraconductivity depending upon the tube radius, temperature and magnetic field
strength is analyzed. The results are qualitatively compared with recent
experimental observations in carbon nanotubes of an inherent transition to the
superconducting state and pronounced thermodynamic fluctuations above .
The application of our results to single-wall and multi-wall carbon nanotubes
as well as ropes of nanotubes is discussed.Comment: 7 pages, 1 figur
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 measured for the tunneling
density of states in carbon nanotubes. We predict that further reduction of
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
Towards realistic implementations of a Majorana surface code
Surface codes have emerged as promising candidates for quantum information
processing. Building on the previous idea to realize the physical qubits of
such systems in terms of Majorana bound states supported by topological
semiconductor nanowires, we show that the basic code operations, namely
projective stabilizer measurements and qubit manipulations, can be implemented
by conventional tunnel conductance probes and charge pumping via
single-electron transistors, respectively. The simplicity of the access scheme
suggests that a functional code might be in close experimental reach.Comment: 5 pages, 1 p. suppl.mat, PRL in pres
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
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