44 research outputs found
Probing spin-charge separation in a Tomonaga-Luttinger liquid
In a one-dimensional (1D) system of interacting electrons, excitations of
spin and charge travel at different speeds, according to the theory of a
Tomonaga-Luttinger Liquid (TLL) at low energies. However, the clear observation
of this spin-charge separation is an ongoing challenge experimentally. We have
fabricated an electrostatically-gated 1D system in which we observe spin-charge
separation and also the predicted power-law suppression of tunnelling into the
1D system. The spin-charge separation persists even beyond the low-energy
regime where the TLL approximation should hold. TLL effects should therefore
also be important in similar, but shorter, electrostatically gated wires, where
interaction effects are being studied extensively worldwide.Comment: 11 pages, 4 PDF figures, uses scicite.sty, Science.bs
Probing e-e interactions in a periodic array of GaAs quantum wires
We present the results of non-linear tunnelling spectroscopy between an array
of independent quantum wires and an adjacent two-dimensional electron gas
(2DEG) in a double-quantum-well structure. The two layers are separately
contacted using a surface-gate scheme, and the wires are all very regular, with
dimensions chosen carefully so that there is minimal modulation of the 2DEG by
the gates defining the wires. We have mapped the dispersion spectrum of the 1D
wires down to the depletion of the last 1D subband by measuring the conductance
\emph{G} as a function of the in-plane magnetic field \emph{B}, the interlayer
bias and the wire gate voltage. There is a strong suppression of
tunnelling at zero bias, with temperature and dc-bias dependences consistent
with power laws, as expected for a Tomonaga-Luttinger Liquid caused by
electron-electron interactions in the wires. In addition, the current peaks fit
the free-electron model quite well, but with just one 1D subband there is extra
structure that may indicate interactions.Comment: 3 pages, 3 figures; formatting correcte
Harvesting dissipated energy with a mesoscopic ratchet.
The search for new efficient thermoelectric devices converting waste heat into electrical energy is of major importance. The physics of mesoscopic electronic transport offers the possibility to develop a new generation of nanoengines with high efficiency. Here we describe an all-electrical heat engine harvesting and converting dissipated power into an electrical current. Two capacitively coupled mesoscopic conductors realized in a two-dimensional conductor form the hot source and the cold converter of our device. In the former, controlled Joule heating generated by a voltage-biased quantum point contact results in thermal voltage fluctuations. By capacitive coupling the latter creates electric potential fluctuations in a cold chaotic cavity connected to external leads by two quantum point contacts. For unequal quantum point contact transmissions, a net electrical current is observed proportional to the heat produced.The ERC Advanced Grant 228273 is acknowledged.This is the author accepted manuscript. The final version is available from NPG at http://www.nature.com/ncomms/2015/150401/ncomms7738/abs/ncomms7738.html
Detecting noise with shot noise using on-chip photon detector.
The high-frequency radiation emitted by a quantum conductor presents a rising interest in quantum physics and condensed matter. However, its detection with microwave circuits is challenging. Here, we propose to use the photon-assisted shot noise for on-chip radiation detection. It is based on the low-frequency current noise generated by the partitioning of photon-excited electrons and holes, which are scattered inside the conductor. For a given electromagnetic coupling to the radiation, the photon-assisted shot noise response is shown to be independent on the nature and geometry of the quantum conductor used for the detection, up to a Fano factor, characterizing the type of scattering mechanism. Ordered in temperature or frequency range, from few tens of mK or GHz to several hundred of K or THz respectively, a wide variety of conductors can be used like Quantum Point Contacts (this work), diffusive metallic or semi-conducting films, graphene, carbon nanotubes and even molecule, opening new experimental opportunities in quantum physics.The ERC Advanced Grant 228273 is acknowledged. We are grateful to P. Jacques for experimental support.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/ncomms713
Quantum Criticality and Novel Phases: Summary and Outlook
This conference summary and outlook provides a personal overview of the
topics and themes of the August 2009 Dresden meeting on quantum criticality and
novel phases. The dichotomy between the local moment and the itinerant views of
magnetism is revisited and refreshed in new materials, new probes and new
theoretical ideas. New universality and apparent zero temperature phases of
matter move us beyond the old ideas of quantum criticality. This is accompanied
by alternative pairing interactions and as yet unidentified phases developing
in the vicinity of quantum critical points. In discussing novel order, the
magnetic analogues of superconductivity are considered as candidate states for
the hidden order that sometimes develops in the vicinity of quantum critical
points in metallic systems. These analogues can be thought of as "pairing" in
the particle-hole channel and are tabulated. This analogy is used to outline a
framework to study the relation between ferromagnetic fluctuations and the
propensity of a metal to nematic type phases which at weak coupling correspond
to Pomeranchuk instabilities. This question can be related to the fundamental
relations of Fermi liquid theory.Comment: Conference summary for the 2009 Dresden Meeting on Quantum
Criticality and Novel Phases. 7 pages and 4 figures. The associated
presentation may be found at
http://www.theory.bham.ac.uk/staff/schofield/talks/Dresden
Electron quantum optics in ballistic chiral conductors
The edge channels of the quantum Hall effect provide one dimensional chiral
and ballistic wires along which electrons can be guided in optics like setup.
Electronic propagation can then be analyzed using concepts and tools derived
from optics. After a brief review of electron optics experiments performed
using stationary current sources which continuously emit electrons in the
conductor, this paper focuses on triggered sources, which can generate
on-demand a single particle state. It first outlines the electron optics
formalism and its analogies and differences with photon optics and then turns
to the presentation of single electron emitters and their characterization
through the measurements of the average electrical current and its
correlations. This is followed by a discussion of electron quantum optics
experiments in the Hanbury-Brown and Twiss geometry where two-particle
interferences occur. Finally, Coulomb interactions effects and their influence
on single electron states are considered
Manipulating the Tomonaga-Luttinger exponent by electric field modulation
We establish a theoretical framework for artificial control of the power-law
singularities in Tomonaga-Luttinger liquid states. The exponent governing the
power-law behaviors is found to increase significantly with an increase in the
amplitude of the periodic electric field modulation applied externally to the
system. This field-induced shift in the exponent indicates the tunability of
the transport properties of quasi-one-dimensional electron systems.Comment: 7 pages, 3 figure
Quantum interference and spin-charge separation in a disordered Luttinger liquid
We study the influence of spin on the quantum interference of interacting
electrons in a single-channel disordered quantum wire within the framework of
the Luttinger liquid (LL) model. The nature of the electron interference in a
spinful LL is particularly nontrivial because the elementary bosonic
excitations that carry charge and spin propagate with different velocities. We
extend the functional bosonization approach to treat the fermionic and bosonic
degrees of freedom in a disordered spinful LL on an equal footing. We analyze
the effect of spin-charge separation at finite temperature both on the spectral
properties of single-particle fermionic excitations and on the conductivity of
a disordered quantum wire. We demonstrate that the notion of weak localization,
related to the interference of multiple-scattered electron waves and their
decoherence due to electron-electron scattering, remains applicable to the
spin-charge separated system. The relevant dephasing length, governed by the
interplay of electron-electron interaction and spin-charge separation, is found
to be parametrically shorter than in a spinless LL. We calculate both the
quantum (weak localization) and classical (memory effect) corrections to the
conductivity of a disordered spinful LL. The classical correction is shown to
dominate in the limit of high temperature.Comment: 23 pages, 16 figures, 1 tabl
Wigner crystal in snaked nanochannels
We study properties of Wigner crystal in snaked nanochannels and show that
they are characterized by conducting sliding phase at low charge densities and
insulating pinned phase emerging above a certain critical charge density. The
transition between these phases has a devil's staircase structure typical for
the Aubry transition in dynamical maps and the Frenkel-Kontorova model. We
discuss implications of this phenomenon for charge density waves in
quasi-one-dimensional organic conductors and for supercapacitors in nanopore
materials.Comment: 4 pages, 6 figs, research at http://www.quantware.ups-tlse.f