5,667 research outputs found
The chiral symplectic universality class
We report a numerical investigation of localization in the SU(2) model
without diagonal disorder. At the band center, chiral symmetry plays an
important role. Our results indicate that states at the band center are
critical. States away from the band center but not too close to the edge of the
spectrum are metallic as expected for Hamiltonians with symplectic symmetry.Comment: accepted in Proceedings of Localisation 2002 Conference, Tokyo, Japan
(to be published as supplement of J. Phys. Soc. Japan
Fano resonances as a probe of phase coherence in quantum dots
In the presence of direct trajectories connecting source and drain contacts,
the conductance of a quantum dot may exhibit resonances of the Fano type. Since
Fano resonances result from the interference of two transmission pathways,
their lineshape (as described by the Fano parameter q) is sensitive to
dephasing in the quantum dot. We show that under certain circumstances the
dephasing time can be extracted from a measurement of q for a single resonance.
We also show that q fluctuates from level to level, and calculate its
probability distribution for a chaotic quantum dot. Our results are relevant to
recent experiments by Goeres et al.Comment: 4 pages, 3 figures; published versio
Rectification of displacement currents in an adiabatic electron pump
Rectification of ac displacement currents generated by periodic variation of
two independent gate voltages of a quantum dot can lead to a dc voltage linear
in the frequency. The presence of this rectified displacement current could
account for the magnetic field symmetry observed in a recent measurement on an
adiabatic quantum electron pump by Switkes et al. [Science 283, 1905 (1999)].Comment: 2 pages, RevTeX; 1 figur
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
A spin pump turnstile: parametric pumping of a spin-polarized current through a nearly-closed quantum dot
We investigate parametric pumping of a spin-polarized current through a
nearly-closed quantum dot in a perpendicular magnetic field. Pumping is
achieved by tuning the tunnel couplings to the left and right lead - thereby
operating the quantum dot as a turnstile - and changing either the magnetic
field or a gate-voltage. We analyze the quantum dynamics of a pumping cycle and
the limiting time scales for operating the quantum dot turnstile as a pure spin
pump. The proposed device can be used as a fully controllable double-sided and
bipolar spin filter and to inject spins "on demand".Comment: 5 pages, 2 figures, one reference correcte
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