We report the observation of an unpredictable behavior of a simple, two-path, electron interferometer. Utilizing an electronic analog of the well-known optical Mach-Zehnder interferometer, with current carrying edge channels in the quantum Hall effect regime, we measured high contrast Aharonov-Bohm (AB) oscillations. Surprisingly, the amplitude of the oscillations varied with energy in a lobe fashion, namely, with distinct maxima and zeros (namely, no AB oscillations) in between. Moreover, the phase of the AB oscillations was constant throughout each lobe period but slipped abruptly by pi at each zero. The periodicity of the lobes defines a new energy scale, which may be a general characteristic of quantum coherence of interfering electrons.
Das Buch wendet sich an Theoretiker wie auch Experimentatoren, die auf dem Gebiet der Festkfirperphysik arbeiten. E s kann aber auch Physik-Studenten der hoheren Studienjahre mit der Spezialisierungsrichtung FestkGrperphysik empfohlen werden.nT. JOHN
PACS. 73.23.-b -Mesoscopic systems. PACS. 72.10.-d -Theory of electronic transport; scattering mechanisms.Abstract. -We consider the dephasing of an one-electron state in a quantum dot due to charge fluctuations in a biased quantum point contact coupled to the dot capacitively. The contribution to the dephasing rate due to the bias depends on temperature and bias in the same way as shot-noise in the point contact at zero frequency, but do not follow the |t| 2 (1 − |t| 2 ) suppression.Typeset using EURO-L A T E X
A confined system of non-interacting electrons, subject to the combined
effect of a time-dependent potential and different external
chemical-potentials, is considered. The current flowing through such a system
is obtained for arbitrary strengths of the modulating potential, using the
adiabatic approximation in an iterative manner. A new formula is derived for
the charge pumped through an un-biased system (all external chemical potentials
are kept at the same value); It reproduces the Brouwer formula for a
two-terminal nanostructure. The formalism presented yields the effect of the
chemical potential bias on the pumped charge on one hand, and the modification
of the Landauer formula (which gives the current in response to a constant
chemical-potential difference) brought about by the modulating potential on the
other. Corrections to the adiabatic approximation are derived and discussed.Comment: 8 pages, 2 figure
The reduced BCS Hamiltonian for a metallic grain with a finite number of
electrons is considered. The crossover between the ultrasmall regime, in which
the level spacing, $d$, is larger than the bulk superconducting gap, $\Delta$,
and the small regime, where $\Delta \gtrsim d$, is investigated analytically
and numerically. The condensation energy, spin magnetization and tunneling peak
spectrum are calculated analytically in the ultrasmall regime, using an
approximation controlled by $1/\ln N$ as small parameter, where $N$ is the
number of interacting electron pairs. The condensation energy in this regime is
perturbative in the coupling constant $\lambda$, and is proportional to $d N
\lambda^2 = \lambda^2 \omega_D$. We find that also in a large regime with
$\Delta>d$, in which pairing correlations are already rather well developed,
the perturbative part of the condensation energy is larger than the singular,
BCS, part. The condition for the condensation energy to be well approximated by
the BCS result is found to be roughly $\Delta > \sqrt{d \omega_D}$. We show how
the condensation energy can, in principle, be extracted from a measurement of
the spin magnetization curve, and find a re-entrant susceptibility at zero
temperature as a function of magnetic field, which can serve as a sensitive
probe for the existence of superconducting correlations in ultrasmall grains.
Numerical results are presented which suggest that in the large $N$ limit the
1/N correction to the BCS result for the condensation energy is larger than
$\Delta$.Comment: 17 pages, 7 figures, Submitted to Phys. Rev.
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