174 research outputs found
Particle-hole symmetric Luttinger liquids in a quantum Hall circuit
We report current transmission data through a split-gate constriction
fabricated onto a two-dimensional electron system in the integer quantum Hall
(QH) regime. Split-gate biasing drives inter-edge backscattering and is shown
to lead to suppressed or enhanced transmission, in marked contrast with the
expected linear Fermi-liquid behavior. This evolution is described in terms of
particle-hole symmetry and allows us to conclude that an unexpected class of
gate-controlled particle-hole-symmetric chiral Luttinger Liquids (CLLs) can
exist at the edges of our QH circuit. These results highlight the role of
particle-hole symmetry on the properties of CLL edge states.Comment: 4 pages, 4 figure
Tuning non-linear charge transport between integer and fractional quantum Hall states
Controllable point junctions between different quantum Hall phases are a
necessary building block for the development of mesoscopic circuits based on
fractionally-charged quasiparticles. We demonstrate how particle-hole duality
can be exploited to realize such point-contact junctions. We show an
implementation for the case filling factors and in which
both the fractional filling and the coupling strength can be finely and
independently tuned. A peculiar crossover from insulating to conducting
behavior as goes from 1/3 to 1 is observed. These results highlight the
key role played on inter-edge tunneling by local charge depletion at the point
contact.Comment: 4 pages, 3 figures, suppl.ma
Noise thermometry applied to thermoelectric measurements in InAs nanowires
We apply noise thermometry to characterize charge and thermoelectric
transport in single InAs nanowires (NWs) at a bath temperature of 4.2 K. Shot
noise measurements identify elastic diffusive transport in our NWs with
negligible electron-phonon interaction. This enables us to set up a measurement
of the diffusion thermopower. Unlike in previous approaches, we make use of a
primary electronic noise thermometry to calibrate a thermal bias across the NW.
In particular, this enables us to apply a contact heating scheme, which is much
more efficient in creating the thermal bias as compared to conventional
substrate heating. The measured thermoelectric Seebeck coefficient exhibits
strong mesoscopic fluctuations in dependence on the back-gate voltage that is
used to tune the NW carrier density. We analyze the transport and
thermoelectric data in terms of approximate Mott's thermopower relation and to
evaluate a gate-voltage to Fermi energy conversion factor
Local noise in a diffusive conductor
The control and measurement of local non-equilibrium configurations is of
utmost importance in applications on energy harvesting, thermoelectrics and
heat management in nano-electronics. This challenging task can be achieved with
the help of various local probes, prominent examples including superconducting
or quantum dot based tunnel junctions, classical and quantum resistors, and
Raman thermography. Beyond time-averaged properties, valuable information can
also be gained from spontaneous fluctuations of current (noise). From these
perspective, however, a fundamental constraint is set by current conservation,
which makes noise a characteristic of the whole conductor, rather than some
part of it. Here we demonstrate how to remove this obstacle and pick up a local
noise temperature of a current biased diffusive conductor with the help of a
miniature noise probe. This approach is virtually noninvasive and extends
primary local measurements towards strongly non-equilibrium regimes.Comment: minor revision, accepted in Scientific Report
Classical-to-stochastic Coulomb blockade cross-over in aluminum arsenide wires
We report low-temperature differential conductance measurements in aluminum
arsenide cleaved-edge overgrown quantum wires in the pinch-off regime. At zero
source-drain bias we observe Coulomb blockade conductance resonances that
become vanishingly small as the temperature is lowered below . We
show that this behavior can be interpreted as a classical-to-stochastic Coulomb
blockade cross-over in a series of asymmetric quantum dots, and offer a
quantitative analysis of the temperature-dependence of the resonances
lineshape. The conductance behavior at large source-drain bias is suggestive of
the charge density wave conduction expected for a chain of quantum dots.Comment: version 2: new figure 4, refined discussio
Bethe-Ansatz density-functional theory of ultracold repulsive fermions in one-dimensional optical lattices
We present an extensive numerical study of ground-state properties of
confined repulsively interacting fermions on one-dimensional optical lattices.
Detailed predictions for the atom-density profiles are obtained from parallel
Kohn-Sham density-functional calculations and quantum Monte Carlo simulations.
The density-functional calculations employ a Bethe-Ansatz-based local-density
approximation for the correlation energy, which accounts for Luttinger-liquid
and Mott-insulator physics. Semi-analytical and fully numerical formulations of
this approximation are compared with each other and with a cruder
Thomas-Fermi-like local-density approximation for the total energy. Precise
quantum Monte Carlo simulations are used to assess the reliability of the
various local-density approximations, and in conjunction with these allow to
obtain a detailed microscopic picture of the consequences of the interplay
between particle-particle interactions and confinement in one-dimensional
systems of strongly correlated fermions.Comment: 14 pages, 11 figures, 1 table, submitte
Transport through constricted quantum Hall edge systems: beyond the quantum point contact
Motivated by surprises in recent experimental findings, we study transport in
a model of a quantum Hall edge system with a gate-voltage controlled
constriction. A finite backscattered current at finite edge-bias is explained
from a Landauer-Buttiker analysis as arising from the splitting of edge current
caused by the difference in the filling fractions of the bulk () and
constriction () quantum Hall fluid regions. We develop a hydrodynamic
theory for bosonic edge modes inspired by this model. The constriction region
splits the incident long-wavelength chiral edge density-wave excitations among
the transmitting and reflecting edge states encircling it. The competition
between two interedge tunneling processes taking place inside the constriction,
related by a quasiparticle-quasihole (qp-qh) symmetry, is accounted for by
computing the boundary theories of the system. This competition is found to
determine the strong coupling configuration of the system. A separatrix of
qp-qh symmetric gapless critical states is found to lie between the relevant RG
flows to a metallic and an insulating configuration of the constriction system.
This constitutes an interesting generalisation of the Kane-Fisher quantum
impurity model. The features of the RG phase diagram are also confirmed by
computing various correlators and chiral linear conductances of the system. In
this way, our results find excellent agreement with many recent puzzling
experimental results for the cases of . We also discuss and
make predictions for the case of a constriction system with .Comment: 18 pages, 9 figure
InAs nanowire hot-electron Josephson transistor
At a superconductor (S)-normal metal (N) junction pairing correlations can
"leak-out" into the N region. This proximity effect [1, 2] modifies the system
transport properties and can lead to supercurrent flow in SNS junctions [3].
Recent experimental works showed the potential of semiconductor nanowires (NWs)
as building blocks for nanometre-scale devices [4-7], also in combination with
superconducting elements [8-12]. Here, we demonstrate an InAs NW Josephson
transistor where supercurrent is controlled by hot-quasiparticle injection from
normal-metal electrodes. Operational principle is based on the modification of
NW electron-energy distribution [13-20] that can yield reduced dissipation and
high-switching speed. We shall argue that exploitation of this principle with
heterostructured semiconductor NWs opens the way to a host of
out-of-equilibrium hybrid-nanodevice concepts [7, 21].Comment: 6 pages, 6 color figure
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