Finite-temperature Fermi-edge singularity in tunneling studied using random telegraph signals

We show that random telegraph signals in metal-oxide-silicon transistors at millikelvin temperatures provide a powerful means of investigating tunneling between a two-dimensional electron gas and a single defect state. The tunneling rate shows a peak when the defect level lines up with the Fermi energy, in excellent agreement with theory of the Fermi-edge singularity at finite temperature. This theory also indicates that defect levels are the origin of the dissipative two-state systems observed previously in similar devices.Comment: 5 pages, REVTEX, 3 postscript figures included with epsfi

Is weak temperature dependence of electron dephasing possible?

The first-principle theory of electron dephasing by disorder-induced two state fluctuators is developed. There exist two mechanisms of dephasing. First, dephasing occurs due to direct transitions between the defect levels caused by inelastic electron-defect scattering. The second mechanism is due to violation of the time reversal symmetry caused by time-dependent fluctuations of the scattering potential. These fluctuations originate from an interaction between the dynamic defects and conduction electrons forming a thermal bath. The first contribution to the dephasing rate saturates as temperature decreases. The second contribution does not saturate, although its temperature dependence is rather weak, $\propto T^{1/3}$. The quantitative estimates based on the experimental data show that these mechanisms considered can explain the weak temperature dependence of the dephasing rate in some temperature interval. However, below some temperature dependent on the model of dynamic defects the dephasing rate tends rapidly to zero. The relation to earlier studies of the dephasing caused by the dynamical defects is discussed.Comment: 14 pages, 6 figures, submitted to PR

Inbreeding, outbreeding, infant growth, and size dimorphism in captive Indian rhinoceros (Rhinoceros unicornis)

Effects of inbreeding and outbreeding on gestation period, birth mass, infant mortality, and growth, as well as the ontogeny of sexual size dimorphism, were analyzed in captive Indian rhinoceros (Rhinoceros unicornis L., 1758) using studbook data. Neither gestation period nor birth mass were affected by inbreeding. However, inbred calves grew slower and had a lower mortality rate than non-inbred ones. It is suggested that the severe bottleneck experienced in the early twentieth century by the Kaziranga population, from which most captive-born Indian rhinoceroses descend, resulted in strong inbreeding with consequent purging of recessive lethal alleles. Outbred individuals (offspring of matings between individuals from the Kaziranga and the Chitwan populations) had a higher infant mortality rate, suggesting that the two populations are genetically partially incompatible. Among captive individuals, adult males were found to be heavier (2300 kg) and larger (shoulder height = 172 cm) than females (1800 kg, 160 cm). There were, however, no sex differences in gestation period, birth mass, or infant growth. This suggests that sexual dimorphism in adults is the result of a longer growth period in males rather than a difference in growth rate between the sexes