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/Cd$_x$Hg$_{1-x}$Te/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 $(10-15)$ 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/Cd$_x$Hg$_{1-x}$Te quantum wells with a width $(8-20)$~nm has been studied experimentally by magnetotransport effects and theoretically in framework $4$-bands $kP$-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 $p< 5.5\times 10^{11}$~cm$^{-2}$. Such degeneracy does not agree with the calculations of the spectrum performed within the framework of the $4$-bands $kP$-method for symmetric quantum wells. These calculations show that the top of the valence band consists of four spin-degenerate extremes located at $k\neq 0$ (valleys) which gives the total degeneracy $K=8$. 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 $K=4$. 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 $K=2$. It is noteworthy that for our case two-fold degeneracy occurs due to degeneracy of two single-spin valleys. The hole effective mass ($m_h$) determined from analysis of the temperature dependence of the amplitude of the SdH oscillations show that $m_h$ is equal to $(0.25\pm0.02)\,m_0$ and weakly increases with the hole density. Such a value of $m_h$ and its dependence on the hole density are in a good agreement with the calculated effective mass.Comment: 8 pages, 11 figure

Superhigh-frequency characteristics of optical modulators on the basis of InGaAlAs resonance-tunnel heterostructures

The impedance of InGaAlAs resonance-tunnel heterostructures used for modulation of optical radiation is experimentally studied in the frequency range from 45 to 18 MHz. The dependence of their equivalent circuit on the bias voltage is determined. The spectrum of the harmonics of the current in the resistive frequency multiplication in such structures is calculated. The results confirm that these structures are promising as applied to the frequency multiplication. The effect of frequency multiplication is demonstrated experimentally at low frequencies