6,737 research outputs found
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 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
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
Hanbury Brown and Twiss noise correlations in a topological superconductor beam splitter
We study Hanbury-Brown and Twiss current cross-correlations in a
three-terminal junction where a central topological superconductor (TS)
nanowire, bearing Majorana bound states at its ends, is connected to two normal
leads. Relying on a non-perturbative Green function formalism, our calculations
allow us to provide analytical expressions for the currents and their
correlations at subgap voltages, while also giving exact numerical results
valid for arbitrary external bias. We show that when the normal leads are
biased at voltages and smaller than the gap, the sign of the
current cross-correlations is given by -\mbox{sgn}(V_1 \, V_2). In
particular, this leads to positive cross-correlations for opposite voltages, a
behavior in stark contrast with the one of a standard superconductor, which
provides a direct evidence of the presence of the Majorana zero-mode at the
edge of the TS. We further extend our results, varying the length of the TS
(leading to an overlap of the Majorana bound states) as well as its chemical
potential (driving it away from half-filling), generalizing the boundary TS
Green function to those cases. In the case of opposite bias voltages,
\mbox{sgn}(V_1 \, V_2)=-1, driving the TS wire through the topological
transition leads to a sign change of the current cross-correlations, providing
yet another signature of the physics of the Majorana bound state.Comment: 14 pages, 8 figure
Luttinger liquid behavior in multi-wall carbon nanotubes
The low-energy theory for multi-wall carbon nanotubes including the
long-ranged Coulomb interactions, internal screening effects, and
single-electron hopping between graphite shells is derived and analyzed by
bosonization methods. Characteristic Luttinger liquid power laws are found for
the tunneling density of states, with exponents approaching their Fermi liquid
value only very slowly as the number of conducting shells increases. With minor
modifications, the same conclusions apply to transport in ropes of single-wall
nanotubes.Comment: 4 pages Revte
Giant shot noise from Majorana zero modes in topological trijunctions
The clear-cut experimental identification of Majorana bound states in
transport measurements still poses experimental challenges. We here show that
the zero-energy Majorana state formed at a junction of three topological
superconductor wires is directly responsible for giant shot noise amplitudes,
in particular at low voltages and for small contact transparency. The only
intrinsic noise limitation comes from the current-induced dephasing rate due to
multiple Andreev reflection processes
Transport theory of carbon nanotube Y junctions
We describe a generalization of Landauer-B\"uttiker theory for networks of
interacting metallic carbon nanotubes. We start with symmetric starlike
junctions and then extend our approach to asymmetric systems. While the
symmetric case is solved in closed form, the asymmetric situation is treated by
a mix of perturbative and non-perturbative methods. For N>2 repulsively
interacting nanotubes, the only stable fixed point of the symmetric system
corresponds to an isolated node. Detailed results for both symmetric and
asymmetric systems are shown for N=3, corresponding to carbon nanotube Y
junctions.Comment: submitted to New Journal of Physics, Focus Issue on Carbon Nanotubes,
15 pages, 3 figure
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
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
Electronic Properties of Armchair Carbon Nanotubes : Bosonization Approach
The phase Hamiltonian of armchair carbon nanotubes at half-filling and away
from it is derived from the microscopic lattice model by taking the long range
Coulomb interaction into account. We investigate the low energy properties of
the system using the renormalization group method. At half-filling, the ground
state is a Mott insulator with spin gap, in which the bound states of electrons
at different atomic sublattices are formed. The difference from the recent
results [Phys. Rev. Lett. 79, 5082 (1997)] away half-filling is clarified.Comment: 4 pages, 1 figure, Revte
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