281 research outputs found
Super-Poissonian noise in a Coulomb blockade metallic quantum dot structure
The shot noise of the current through a single electron transistor (SET),
coupled capacitively with an electronic box, is calculated, using the master
equation approach. We show that the noise may be sub-Poissonian or strongly
super-Poissonian, depending mainly on the box parameters and the gate. The
study also supports the idea that not negative differential conductance, but
charge accumulation in the quantum dot, responds for the super-Poissonian noise
observed.Comment: 4 Pages, 3 Figure
Negative polarizability of 2D electrons in HgTe quantum well
The polarizability of electrons occupying the lowest subband of spatial
quantization in CdTe/CdHgTe/CdTe quantum wells is calculated. It is
shown that polarizability in the quantum well without cadmium is negative,
i.e., the displacement of an electron in an electric field applied
perpendicularly to the quantum well plane is opposite to the force acting on
it. The negative polarizability of 2D electrons can reduce the dielectric
constant of quantum wells by up to percent.Comment: 4 pages, 4 figure
The valence band energy spectrum of HgTe quantum wells with inverted band structures
The energy spectrum of the valence band in HgTe/CdHgTe quantum
wells with a width ~nm has been studied experimentally by
magnetotransport effects and theoretically in framework -bands -method.
Comparison of the Hall density with the density found from period of the
Shubnikov-de Haas (SdH) oscillations clearly shows that the degeneracy of
states of the top of the valence band is equal to 2 at the hole density ~cm. Such degeneracy does not agree with the
calculations of the spectrum performed within the framework of the -bands
-method for symmetric quantum wells. These calculations show that the top
of the valence band consists of four spin-degenerate extremes located at (valleys) which gives the total degeneracy . It is shown that taking
into account the "mixing of states" at the interfaces leads to the removal of
the spin degeneracy that reduces the degeneracy to . Accounting for any
additional asymmetry, for example, due to the difference in the mixing
parameters at the interfaces, the different broadening of the boundaries of the
well, etc, leads to reduction of the valleys degeneracy, making . It is
noteworthy that for our case two-fold degeneracy occurs due to degeneracy of
two single-spin valleys. The hole effective mass () determined from
analysis of the temperature dependence of the amplitude of the SdH oscillations
show that is equal to and weakly increases with the
hole density. Such a value of and its dependence on the hole density are
in a good agreement with the calculated effective mass.Comment: 8 pages, 11 figure
Coherent oscillations in a Cooper-pair box
This paper is devoted to an analysis of the experiment by Nakamura {\it et
al.} (Nature {\bf 398}, 786 (1999)) on the quantum state control in Josephson
junctions devices. By considering the relevant processes involved in the
detection of the charge state of the box and a realistic description of the
gate pulse we are able to analyze some aspects of the experiment (like the
amplitude of the measurement current) in a quantitative way
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