45 research outputs found
Probing Spin-Charge Separation in Tunnel-Coupled Parallel Quantum Wires
Interactions in one-dimensional (1D) electron systems are expected to cause a
dynamical separation of electronic spin and charge degrees of freedom. A
promising system for experimental observation of this non-Fermi-liquid effect
consists of two quantum wires coupled via tunneling through an extended uniform
barrier. Here we consider the minimal model of an interacting 1D electron
system exhibiting spin-charge separation and calculate the differential
tunneling conductance as well as the density-density response function. Both
quantities exhibit distinct strong features arising from spin-charge
separation. Our analysis of these features within the minimal model neglects
interactions between electrons of opposite chirality and applies therefore
directly to chiral 1D electron systems realized, e.g., at the edge of integer
quantum-Hall systems. Physical insight gained from our results is useful for
interpreting current experiment in quantum wires as our main conclusions still
apply with nonchiral interactions present. In particular, we discuss the effect
of charging due to applied voltages, and the possibility to observe spin-charge
separation in a time-resolved experiment.Comment: 9 pages, 3 figures, expanded version with many detail
On the Current Carried by `Neutral' Quasiparticles
The current should be proportional to the momentum in a Galilean-invariant
system of particles of fixed charge-to-mass ratio, such as an electron liquid
in jellium. However, strongly-interacting electron systems can have phases
characterized by broken symmetry or fractionalization. Such phases can have
neutral excitations which can presumably carry momentum but not current. In
this paper, we show that there is no contradiction: `neutral' excitations {\em
do} carry current in a Galilean-invariant system of particles of fixed
charge-to-mass ratio. This is explicitly demonstrated in the context of spin
waves, the Bogoliubov-de Gennes quasiparticles of a superconductor, the
one-dimensional electron gas, and spin-charge separated systems in 2+1
dimensions. We discuss the implications for more realistic systems, which are
not Galilean-invariant
Phase Separation Models for Cuprate Stripe Arrays
An electronic phase separation model provides a natural explanation for a
large variety of experimental results in the cuprates, including evidence for
both stripes and larger domains, and a termination of the phase separation in
the slightly overdoped regime, when the average hole density equals that on the
charged stripes. Several models are presented for charged stripes, showing how
density waves, superconductivity, and strong correlations compete with quantum
size effects (QSEs) in narrow stripes. The energy bands associated with the
charged stripes develop in the middle of the Mott gap, and the splitting of
these bands can be understood by considering the QSE on a single ladder.Comment: significant revisions: includes island phase, 16 eps figures, revte
How to detect fluctuating order in the high-temperature superconductors
We discuss fluctuating order in a quantum disordered phase proximate to a
quantum critical point, with particular emphasis on fluctuating stripe order.
Optimal strategies for extracting information concerning such local order from
experiments are derived with emphasis on neutron scattering and scanning
tunneling microscopy. These ideas are tested by application to two model
systems - the exactly solvable one dimensional electron gas with an impurity,
and a weakly-interacting 2D electron gas. We extensively review experiments on
the cuprate high-temperature superconductors which can be analyzed using these
strategies. We adduce evidence that stripe correlations are widespread in the
cuprates. Finally, we compare and contrast the advantages of two limiting
perspectives on the high-temperature superconductor: weak coupling, in which
correlation effects are treated as a perturbation on an underlying metallic
(although renormalized) Fermi liquid state, and strong coupling, in which the
magnetism is associated with well defined localized spins, and stripes are
viewed as a form of micro-phase separation. We present quantitative indicators
that the latter view better accounts for the observed stripe phenomena in the
cuprates.Comment: 43 pages, 11 figures, submitted to RMP; extensively revised and
greatly improved text; one new figure, one new section, two new appendices
and more reference
The Serotonin 5-HT7Dro Receptor Is Expressed in the Brain of Drosophila, and Is Essential for Normal Courtship and Mating
The 5-HT7 receptor remains one of the less well characterized
serotonin receptors. Although it has been demonstrated to be involved in the
regulation of mood, sleep, and circadian rhythms, as well as relaxation of
vascular smooth muscles in mammals, the precise mechanisms underlying these
functions remain largely unknown. The fruit fly, Drosophila
melanogaster, is an attractive model organism to study
neuropharmacological, molecular, and behavioral processes that are largely
conserved with mammals. Drosophila express a homolog of the mammalian
5-HT7 receptor, as well as homologs for the mammalian
5-HT1A, and 5-HT2, receptors. Each fly receptor
couples to the same effector pathway as their mammalian counterpart and have
been demonstrated to mediate similar behavioral responses. Here, we report on
the expression and function of the 5-HT7Dro receptor in Drosophila.
In the larval central nervous system, expression is detected postsynaptically in
discreet cells and neuronal circuits. In the adult brain there is strong
expression in all large-field R neurons that innervate the ellipsoid body, as
well as in a small group of cells that cluster with the PDF-positive LNvs
neurons that mediate circadian activity. Following both pharmacological and
genetic approaches, we have found that 5-HT7Dro activity is essential
for normal courtship and mating behaviors in the fly, where it appears to
mediate levels of interest in both males and females. This is the first reported
evidence of direct involvement of a particular serotonin receptor subtype in
courtship and mating in the fly
Angle-resolved photoemission spectroscopy of the cuprate superconductors
This paper reviews the most recent ARPES results on the cuprate
superconductors and their insulating parent and sister compounds, with the
purpose of providing an updated summary of the extensive literature in this
field. The low energy excitations are discussed with emphasis on some of the
most relevant issues, such as the Fermi surface and remnant Fermi surface, the
superconducting gap, the pseudogap and d-wave-like dispersion, evidence of
electronic inhomogeneity and nano-scale phase separation, the emergence of
coherent quasiparticles through the superconducting transition, and many-body
effects in the one-particle spectral function due to the interaction of the
charge with magnetic and/or lattice degrees of freedom. The first part of the
paper introduces photoemission spectroscopy in the context of strongly
interacting systems, along with an update on the state-of-the-art
instrumentation. The second part provides a brief overview of the scientific
issues relevant to the investigation of the low energy electronic structure by
ARPES. The rest of the paper is devoted to the review of experimental results
from the cuprates and the discussion is organized along conceptual lines:
normal-state electronic structure, interlayer interaction, superconducting gap,
coherent superconducting peak, pseudogap, electron self energy and collective
modes. Within each topic, ARPES data from the various copper oxides are
presented.Comment: Reviews of Modern Physics, in press. A HIGH-QUALITY pdf file is
available at http://www.physics.ubc.ca/~damascel/RMP_ARPES.pd