153 research outputs found
Effect of interactions on the noise of chiral Luttinger liquid systems
We analyze the current noise, generated at a quantum point contact in
fractional quantum Hall edge state devices, using the chiral Luttinger liquid
model with an impurity and the associated exact field theoretic solution. We
demonstrate that an experimentally relevant regime of parameters exists where
the noise coincides with the partition noise of independent Laughlin
quasiparticles. However, outside of this regime, this independent particle
picture breaks down and the inclusion of interaction effects is essential to
understand the shot noise.Comment: 4 pages, 3 figures; v2: modified FIG.1, new FIG.
Beyond the Linearity of Current-Voltage Characteristics in Multiwalled Carbon Nanotubes
We present local and non-local electron transport measurements on individual
multi-wall nanotubes for bias voltage between 0 and about 4 V. Local
current-voltage characteristics are quite linear. In contrast, non-local
measurements are highly non-linear; the differential non-local conductance can
even become negative in the high-bias regime. We discuss the relationship
between these results and transport parameters such as the elastic length, the
number of current carrying shells, and the number of conducting modes.Comment: 5 pages, 5 figure
Violation of Kirchhoff's Laws for a Coherent RC Circuit
What is the complex impedance of a fully coherent quantum
resistance-capacitance (RC) circuit at GHz frequencies in which a resistor and
a capacitor are connected in series? While Kirchhoff's laws predict addition of
capacitor and resistor impedances, we report on observation of a different
behavior. The resistance, here associated with charge relaxation, differs from
the usual transport resistance given by the Landauer formula. In particular,
for a single mode conductor, the charge relaxation resistance is half the
resistance quantum, regardless of the transmission of the mode. The new
mesoscopic effect reported here is relevant for the dynamical regime of all
quantum devices
Four-point resistance of individual single-wall carbon nanotubes
We have studied the resistance of single-wall carbon nanotubes measured in a
four-point configuration with noninvasive voltage electrodes. The voltage drop
is detected using multiwalled carbon nanotubes while the current is injected
through nanofabricated Au electrodes. The resistance at room temperature is
shown to be linear with the length as expected for a classical resistor. This
changes at cryogenic temperature; the four-point resistance then depends on the
resistance at the Au-tube interfaces and can even become negative due to
quantum-interference effects.Comment: 4 pages, 4 figure
Finite bias visibility of the electronic Mach-Zehnder interferometer
We present an original statistical method to measure the visibility of
interferences in an electronic Mach-Zehnder interferometer in the presence of
low frequency fluctuations. The visibility presents a single side lobe
structure shown to result from a gaussian phase averaging whose variance is
quadratic with the bias. To reinforce our approach and validate our statistical
method, the same experiment is also realized with a stable sample. It exhibits
the same visibility behavior as the fluctuating one, indicating the intrinsic
character of finite bias phase averaging. In both samples, the dilution of the
impinging current reduces the variance of the gaussian distribution.Comment: 4 pages, 5 figure
Spin-charge separation in two-component Bose-gases
We show that one of the key characteristics of interacting one-dimensional
electronic quantum systems, the separation of spin and charge, can be observed
in a two-component system of bosonic ultracold atoms even close to a competing
phase separation regime. To this purpose we determine the real-time evolution
of a single particle excitation and the single-particle spectral function using
density-matrix renormalization group techniques. Due to efficient bosonic
cooling and good tunability this setup exhibits very good conditions for
observing this strong correlation effect. In anticipation of experimental
realizations we calculate the velocities for spin and charge perturbations for
a wide range of parameters
An On-Demand Coherent Single Electron Source
We report on the electron analog of the single photon gun. On demand single
electron injection in a quantum conductor was obtained using a quantum dot
connected to the conductor via a tunnel barrier. Electron emission is triggered
by application of a potential step which compensates the dot charging energy.
Depending on the barrier transparency the quantum emission time ranges from 0.1
to 10 nanoseconds. The single electron source should prove useful for the
implementation of quantum bits in ballistic conductors. Additionally periodic
sequences of single electron emission and absorption generate a quantized
AC-current
Conserved spin and orbital phase along carbon nanotubes connected with multiple ferromagnetic contacts
We report on spin dependent transport measurements in carbon nanotubes based
multi-terminal circuits. We observe a gate-controlled spin signal in non-local
voltages and an anomalous conductance spin signal, which reveal that both the
spin and the orbital phase can be conserved along carbon nanotubes with
multiple ferromagnetic contacts. This paves the way for spintronics devices
exploiting both these quantum mechanical degrees of freedom on the same
footing.Comment: 8 pages - minor differences with published versio
Carrier drift velocity and edge magnetoplasmons in graphene
We investigate electron dynamics at the graphene edge by studying the
propagation of collective edge magnetoplasmon (EMP) excitations. By timing the
travel of narrow wave-packets on picosecond time scales around exfoliated
samples, we find chiral propagation with low attenuation at a velocity which is
quantized on Hall plateaus. We extract the carrier drift contribution from the
EMP propagation and find it to be slightly less than the Fermi velocity, as
expected for an abrupt edge. We also extract the characteristic length for
Coulomb interaction at the edge and find it to be smaller than for soft,
depletion edge systems.Comment: 5 pages, 3 figures of main text and 6 pages, 6 figures of
supplemental materia
Experimental Test of the High-Frequency Quantum Shot Noise Theory in a Quantum Point Contact
We report on direct measurements of the electronic shot noise of a quantum
point contact at frequencies nu in the range 4-8 GHz. The very small energy
scale used ensures energy independent transmissions of the few transmitted
electronic modes and their accurate knowledge. Both the thermal energy and the
quantum point contact drain-source voltage Vds are comparable to the photon
energy hnu leading to observation of the shot noise suppression when
. Our measurements provide the first complete test of the finite
frequency shot noise scattering theory without adjustable parameters.Comment: Version Published in Phys. Rev. Lett. (Phys. Rev. Lett. 99, 236803
(2007)
- …