992 research outputs found

### Influence of the contacts on the conductance of interacting quantum wires

We investigate how the conductance G through a clean interacting quantum wire
is affected by the presence of contacts and noninteracting leads. The contacts
are defined by a vanishing two-particle interaction to the left and a finite
repulsive interaction to the right or vice versa. No additional single-particle
scattering terms (impurities) are added. We first use bosonization and the
local Luttinger liquid picture and show that within this approach G is
determined by the properties of the leads regardless of the details of the
spatial variation of the Luttinger liquid parameters. This generalizes earlier
results obtained for step-like variations. In particular, no single-particle
backscattering is generated at the contacts. We then study a microscopic model
applying the functional renormalization group and show that the spatial
variation of the interaction produces single-particle backscattering, which in
turn leads to a reduced conductance. We investigate how the smoothness of the
contacts affects G and show that for decreasing energy scale its deviation from
the unitary limit follows a power law with the same exponent as obtained for a
system with a weak single-particle impurity placed in the contact region of the
interacting wire and the leads.Comment: 10 page, 4 figures included, minor changes in the summary, version
accepted for publication in PR

### Probing the intrinsic state of a one-dimensional quantum well with a photon-assisted tunneling

The photon-assisted tunneling (PAT) through a single wall carbon nanotube
quantum well (QW) under influence an external electromagnetic field for probing
of the Tomonaga Luttinger liquid (TLL) state is suggested. The elementary TLL
excitations inside the quantum well are density ($\rho_{\pm}$) and spin
($\sigma_{\pm}$) bosons. The bosons populate the quantized energy levels
$\epsilon^{\rho +}_n =\Delta n/ g$ and $\epsilon^{\rho -(\sigma \pm)}_n =
\Delta n$ where $\Delta = h v_F /L$ is the interlevel spacing, $n$ is an
integer number, $L$ is the tube length, $g$ is the TLL parameter. Since the
electromagnetic field acts on the $\rho_{+}$ bosons only while the neutral
$\rho_{-}$ and $\sigma_{\pm}$ bosons remain unaffected, the PAT spectroscopy
is able of identifying the $\rho_{+}$ levels in the QW setup. The spin
$\epsilon_n^{\sigma+}$ boson levels in the same QW are recognized from Zeeman
splitting when applying a d.c. magnetic field $H \neq 0$ field. Basic TLL
parameters are readily extracted from the differential conductivity curves.Comment: 10 pages, 5 figure

### Study of the charge correlation function in one-dimensional Hubbard heterostructures

We study inhomogeneous one-dimensional Hubbard systems using the density
matrix renormalization group method. Different heterostructures are
investigated whose configuration is modeled varying parameters like the on-site
Coulomb potential and introducing local confining potentials. We investigate
their Luttinger liquid properties through the parameter K_rho, which
characterizes the decay of the density-density correlation function at large
distances. Our main goal is the investigation of possible realization of
engineered materials and the ability to manipulate physical properties by
choosing an appropriate spatial and/or chemical modulation.Comment: 6 pages, 7 figure

### Luttinger liquids with curvature: Density correlations and Coulomb drag effect

We consider the effect of the curvature in fermionic dispersion on the
observable properties of Luttinger liquid (LL). We use the bosonization
technique where the curvature is irrelevant perturbation, describing the decay
of LL bosons (plasmon modes). When possible, we establish the correspondence
between the bosonization and the fermionic approach. We analyze modifications
in density correlation functions due to curvature at finite temperatures, T.
The most important application of our approach is the analysis of the Coulomb
drag by small momentum transfer between two LL, which is only possible due to
curvature. Analyzing the a.c. transconductivity in the one-dimensional drag
setup, we confirm the results by Pustilnik et al. for T-dependence of drag
resistivity, R_{12} ~ T^2 at high and R_{12} ~ T^5 at low temperatures. The
bosonization allows for treating both intra- and inter-wire electron-electron
interactions in all orders, and we calculate exact prefactors in low-T drag
regime. The crossover temperature between the two regimes is T_1 ~ E_F \Delta,
with \Delta relative difference in plasmon velocities. We show that \Delta \neq
0 even for identical wires, due to lifting of degeneracy by interwire
interaction, U_{12}, leading to crossover from R_{12} ~ U_{12}^2 T^2 to R_{12}
\~ T^5/U_{12} at T ~ U_{12}.Comment: 16 pages, 10 figures, REVTE

### The mean energy, strength and width of triple giant dipole resonances

We investigate the mean energy, strength and width of the triple giant dipole
resonance using sum rules.Comment: 12 page

### Sense of Self in Baby Chimpanzees

Philippe Rochat and his colleague tentatively proposed that young infants' propensity to engage in self-perception and systematic exploration of the perceptual consequences of their own action plays and is probably at the origin of an early sense of self: the ecological self. Rochat and Hespos (1997) reported that neonates discriminate between external and self-stimulation. Neonate tended to display significantly more rooting responses (i.e., head turn towards the stimulation with mouth open and tonguing) following external compared to self-stimulation. Rochat et al. (1998) also reported that 2-month-olds showed clear sign of modulation of their oral activity on the pacifier as a function of analog versus non-analog condition. Rochat and his colleague concluded that these observations are interpreted as evidence of self-exploration and the emergence of a sense of self-agency by 2-month-olds. We tried to replicate these findings in infant chimpanzees. We observed rooting responses of three baby chimpanzees in two condition, self-stimulation and external stimulation. In external stimulation condition, the index finger of the experimenter or small stick touched one of the infant's cheeks. In self-stimulation condition, the experimenter took infant's hand and touched his or her cheek with their fingers. In Rochat and Hespos, they recorded and analyzed several measures such as state, head movement, mouth activity and so on. How ever, we analyzed only mouth activities tentatively. We found infant chimpanzees tended to show more rooting responses following external stimulation compared to self-stimulation as well as human infants.
We also carried out sucking experiment with two baby chimpanzees. The experimenter held the pacifier and put the artificial nipple into the infant's mouth. A session started when the infant take the nipple inside the his or her mouth. Auditory stimulus, which was a complex tone comprised of six harmonics with equal intensity, was given to the chimpanzee according to the test condition during their sucking. There were four test conditions and each condition consisted with three types of feedback as follows: 1) silent baseline, contingent, and steady, 2) contingent baseline, 1-sec delay, and 3-sec delay, 3) contingent baseline, 6-sec delay, and 12-sec delay, 4) contingent baseline, 1/2 efficiency, and 1/4 efficiency. In test 1, one infant chimpanzee showed decrease of the minimum pressure of sucking in the contingent condition. In test 2, one subject showed shorter intervals of sucking in 3-sec delay condition. This seems to be similar to human infant's. We may be able to postulate ecological self in baby chimpanzees according to the self-exploration. In test 3 and 4, we did not obtain any effects of stimulus conditions. Results of these studies. These studies were conducted as the parts of the chimpanzee development project in Primate Research Institute, Kyoto University, organized by Professor Tetsuro Matsuzawa

### Tomonaga-Luttinger liquid correlations and Fabry-Perot interference in conductance and finite-frequency shot noise in a single-walled carbon nanotube

We present a detailed theoretical investigation of transport through a
single-walled carbon nanotube (SWNT) in good contact to metal leads where weak
backscattering at the interfaces between SWNT and source and drain reservoirs
gives rise to electronic Fabry-Perot (FP) oscillations in conductance and shot
noise. We include the electron-electron interaction and the finite length of
the SWNT within the inhomogeneous Tomonaga-Luttinger liquid (TLL) model and
treat the non-equilibrium effects due to an applied bias voltage within the
Keldysh approach. In low-frequency transport properties, the TLL effect is
apparent mainly via power-law characteristics as a function of bias voltage or
temperature at energy scales above the finite level spacing of the SWNT. The
FP-frequency is dominated by the non-interacting spin mode velocity due to two
degenerate subbands rather than the interacting charge velocity. At higher
frequencies, the excess noise is shown to be capable of resolving the
splintering of the transported electrons arising from the mismatch of the
TLL-parameter at the interface between metal reservoirs and SWNT. This dynamics
leads to a periodic shot noise suppression as a function of frequency and with
a period that is determined solely by the charge velocity. At large bias
voltages, these oscillations are dominant over the ordinary FP-oscillations
caused by two weak backscatterers. This makes shot noise an invaluable tool to
distinguish the two mode velocities in the SWNT.Comment: 20 pages, 9 figure

### Generalized Tomonaga-Schwinger equation from the Hadamard formula

A generalized Tomonaga--Schwinger equation, holding on the entire boundary of
a {\em finite} spacetime region, has recently been considered as a tool for
studying particle scattering amplitudes in background-independent quantum field
theory. The equation has been derived using lattice techniques under
assumptions on the existence of the continuum limit. Here I show that in the
context of continuous euclidean field theory the equation can be directly
derived from the functional integral formalism, using a technique based on
Hadamard's formula for the variation of the propagator.Comment: 11 pages, no figure

### Phonon Effects on Spin-Charge Separation in One Dimension

Phonon effects on spin-charge separation in one dimension are investigated
through the calculation of one-electron spectral functions in terms of the
recently developed cluster perturbation theory together with an optimized
phonon approach. It is found that the retardation effect due to the finiteness
of phonon frequency suppresses the spin-charge separation and eventually makes
it invisible in the spectral function. By comparing our results with
experimental data of TTF-TCNQ, it is observed that the electron-phonon
interaction must be taken into account when interpreting the ARPES data.Comment: 5 pages, 5 figures, minor differences with the published version in
Physical Review Letter

### Tails of the dynamical structure factor of 1D spinless fermions beyond the Tomonaga approximation

We consider one-dimensional (1D) interacting spinless fermions with a
non-linear spectrum in a clean quantum wire (non-linear bosonization). We
compute diagrammatically the 1D dynamical structure factor, S(\om,q), beyond
the Tomonaga approximation focusing on it's tails, |\om| \gg vq, {\it i.e.}
the 2-pair excitation continuum due to forward scattering. Our methodology
reveals three classes of diagrams: two "chiral" classes which bring divergent
contributions in the limits \om \to \pm vq, {\it i.e.} near the single-pair
excitation continuum, and a "mixed" class (so-called Aslamasov-Larkin or
Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be
satisfied. We relate our approach to the T=0 ones present in the literature. We
also consider the $T\not=0$ case and show that the 2-pair excitation continuum
dominates the single-pair one in the range: |q|T/k_F \ll \om \mp vq \ll T
(substantial for $q \ll k_F$). As applications we first derive the
small-momentum optical conductivity due to forward scattering: \sigma \sim
1/\om for T \ll \om and \sigma \sim T/\om^2 for T \gg \om. Next, within
the $2-$pair excitation continuum, we show that the attenuation rate of a
coherent mode of dispersion $\Omega_q$ crosses over from $\gamma_q \propto
\Omega_q (q/k_F)^2$, {\it e.g.} $\gamma_q \sim |q|^3$ for an acoustic mode, to
$\gamma_q \propto T (q/k_F)^2$, independent of $\Omega_q$, as temperature
increases. Finally, we show that the $2-$pair excitation continuum yields
subleading curvature corrections to the electron-electron scattering rate:
\tau^{-1} \propto V^2 T + V^4 T^3/\eps_F^2, where $V$ is the dimensionless
strength of the interaction.Comment: (v4) Published version. Details of calculations given (/ referee's
comments). No change in previous results. 13 pages, 4 figures. (v3) Extended
version (/ referee's comments and recent literature). No change in previous
results. 8 pages, 4 figures. (v2) 4 pages, 4 figures. Submitted version
(rapid note in EPJB). Kinetic arguments reduced to a footnote. 2 references
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