505 research outputs found
Fluctuating "order parameter" for a quantum chaotic system with partially broken time-reversal symmetry
The functional defined as the squared modulus of the spatial average of the
wave function squared, plays the role of an ``order parameter'' for the
transition between Hamiltonian ensembles with orthogonal and unitary symmetry.
Upon breaking time-reversal symmetry, the order parameter crosses over from one
to zero. We compute its distribution in the crossover regime and find that it
has large fluctuations around the ensemble average. These fluctuations imply
long-range spatial correlations in the eigenfunction and non-Gaussian
perturbations of eigenvalues, in precise agreement with results by Fal'ko and
Efetov and by Taniguchi, Hashimoto, Simons, and Altshuler. As a third
implication of the order-parameter fluctuations we find correlations in the
response of an eigenvalue to independent perturbations of the system.Comment: 4 pages, REVTeX-3.0, 1 figure. Reference added to Y. V. Fyodorov and
A. D. Mirlin, Phys. Rev. B 51, 13403 (1995
Thermopower of Single-Channel Disordered and Chaotic Conductors
We show (analytically and by numerical simulation) that the zero-temperature
limit of the distribution of the thermopower S of a one-dimensional disordered
wire in the localized regime is a Lorentzian, with a disorder-independent width
of 4 pi^3 k_B^2 T/3e\Delta (where T is the temperature and \Delta the mean
level spacing). Upon raising the temperature the distribution crosses over to
an exponential form exp(-2|S|eT/\Delta). We also consider the case of a chaotic
quantum dot with two single-channel ballistic point contacts. The distribution
of S then has a cusp at S=0 and a tail |S|^{-1-\beta} log|S| for large S (with
\beta=1,2 depending on the presence or absence of time-reversal symmetry).Comment: To be published in Superlattices and Microstructures, special issue
on the occasion of Rolf Landauer's 70th birthda
Distribution of parametric conductance derivatives of a quantum dot
The conductance G of a quantum dot with single-mode ballistic point contacts
depends sensitively on external parameters X, such as gate voltage and magnetic
field. We calculate the joint distribution of G and dG/dX by relating it to the
distribution of the Wigner-Smith time-delay matrix of a chaotic system. The
distribution of dG/dX has a singularity at zero and algebraic tails. While G
and dG/dX are correlated, the ratio of dG/dX and is independent
of G. Coulomb interactions change the distribution of dG/dX, by inducing a
transition from the grand-canonical to the canonical ensemble. All these
predictions can be tested in semiconductor microstructures or microwave
cavities.Comment: 4 pages, RevTeX, 3 figure
The Thermopower of Quantum Chaos
The thermovoltage of a chaotic quantum dot is measured using a current
heating technique. The fluctuations in the thermopower as a function of
magnetic field and dot shape display a non-Gaussian distribution, in agreement
with simulations using Random Matrix Theory. We observe no contributions from
weak localization or short trajectories in the thermopower.Comment: 4 pages, 3 figures, corrected: accidently omitted author in the
Authors list, here (not in the article
Berry phase and adiabaticity of a spin diffusing in a non-uniform magnetic field
An electron spin moving adiabatically in a strong, spatially non-uniform
magnetic field accumulates a geometric phase or Berry phase, which might be
observable as a conductance oscillation in a mesoscopic ring. Two contradicting
theories exist for how strong the magnetic field should be to ensure
adiabaticity if the motion is diffusive. To resolve this controversy, we study
the effect of a non-uniform magnetic field on the spin polarization and on the
weak-localization effect. The diffusion equation for the Cooperon is solved
exactly. Adiabaticity requires that the spin-precession time is short compared
to the elastic scattering time - it is not sufficient that it is short compared
to the diffusion time around the ring. This strong condition severely
complicates the experimental observation.Comment: 16 pages REVTEX, including 3 figure
Measurement of the Probability Distribution of Total Transmission in Random Waveguides
Measurements have been made of the probability distribution of total
transmission of microwave radiation in waveguides filled with randomly
positioned scatterers which would have values of the dimensionless conductance
g near unity. The distributions are markedly non-Gaussian and have exponential
tails. The measured distributions are accurately described by diagrammatic and
random matrix calculations carried out for nonabsorbing samples in the limit g
>> 1 when g is expressed in terms of the variance of the distribution, which
equals the degree of long-range intensity correlation across the output face of
the sample.Comment: 5 pages, 5 post script figures, RevTe
Berry phase and persistent current in disordered mesoscopic rings
A novel quantum interference effect in disordered quasi-one-dimensional rings
in the inhomogeneous magnetic field is reported. We calculate the canonical
disorder averaged persistent current using the diagrammatic perturbation
theory. It is shown that within the adiabatic regime the average current
oscillates as a function of the geometric flux which is related to the Berry
phase and the period becomes half the value of the case of a single
one-dimensional ring. We also discuss the magnetic dephasing effect on the
averaged current.Comment: 6 pages, RevTeX, 2 figures. To appear in Phys. Rev. B Rapid
Communications Vol.60 No.12 (1999
Shot noise of series quantum point contacts intercalating chaotic cavities
Shot noise of series quantum point contacts forming a sequence of cavities in
a two dimensional electron gas are studied theoretically and experimentally.
Noise in such a structure originates from local scattering at the point
contacts as well as from chaotic motion of the electrons in the cavities. We
found that the measured shot noise is in reasonable agreement with our
theoretical prediction taking the cavity noise into account.Comment: 4 pages, 5 figure
From planning the port/city to planning the port-city : exploring the economic interface in European port cities
In last three decades, planning agencies of most ports have institutionally evolved into a (semi-) independent port authority. The rationale behind this process is that port authorities are able to react more quickly to changing logistical and spatial preferences of maritime firms, hence increasing the competitiveness of ports. Although these dedicated port authorities have proven to be largely successful, new economic, social, and environmental challenges are quickly catching up on these port governance models, and particularly leads to (spatial) policy ‘conflicts’ between port and city. This chapter starts by assessing this conflict and argue that the conflict is partly a result of dominant—often also academic—spatial representations of the port city as two separate entities. To escape this divisive conception of contemporary port cities, this chapter presents a relational visualisation method that is able to analyse the economic interface between port and city. Based on our results, we reflect back on our proposition and argue that the core challenge today for researchers and policy makers is acknowledging the bias of port/city, being arguably a self-fulfilling prophecy. Hence, we turn the idea of (planning the) port/city conflicts into planning the port-city’s strengths and weaknesses
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