Loss of quantum coherence due to non-stationary glass fluctuations

Low-temperature dynamics of insulating glasses is dominated by a macroscopic concentration of tunneling two-level systems (TTLS). The distribution of the switching/relaxation rates of TTLS is exponentially broad, which results in non-equilibrium state of the glass at arbitrarily long time-scales. Due to the electric dipolar nature, the switching TTLS generate fluctuating electromagnetic fields. We study the effect of the non-thermal slow fluctuators on the dephasing of a solid state qubit. We find that at low enough temperatures, non-stationary contribution can dominate the stationary (thermal) one, and discuss how this effect can be minimized.Comment: 4 page

Zero-bias anomalies of point contact resistance due to adiabatic electron renormalization of dynamical defects

We study effect of the adiabatic electron renormalization on the parameters of the dynamical defects in the ballistic metallic point contact. The upper energy states of the ``dressed'' defect are shown to give a smaller contribution to a resistance of the contact than the lower energy ones. This holds both for the "classical" renormalization related to defect coupling with average local electron density and for the "mesoscopic" renormalization caused by the mesoscopic fluctuations of electronic density the dynamical defects are coupled with. In the case of mesoscopic renormalization one may treat the dynamical defect as coupled with Friedel oscillations originated by the other defects, both static and mobile. Such coupling lifts the energy degeneracy of the states of the dynamical defects giving different mesoscopic contribution to resistance, and provides a new model for the fluctuator as for the object originated by the electronic mesoscopic disorder rather than by the structural one. The correlation between the defect energy and the defect contribution to the resistance leads to zero-temperature and zero-bias anomalies of the point contact resistance. A comparison of these anomalies with those predicted by the Two Channel Kondo Model (TCKM) is made. It is shown, that although the proposed model is based on a completely different from TCKM physical background, it leads to a zero-bias anomalies of the point contact resistance, which are qualitatively similar to TCKM predictions.Comment: 6 pages, to be published in Phys. Rev.

Study of Genotype X Environment Interaction in Alfalfa Forage Yield

The response of alfalfa (Medicago sativa L.) forage yield to eight Alberta test sites was studied for the 1990 and 1991 production years. Cluster analysis was used to group locations and cultivars. Analyses of variances indicated genotype x environment (location) interaction for the first cut yield, the total yield and the difference between first and second cut yields. The Brooks, Bow Island (irrigation), Bow Island (dryland) and Provost locations always clustered together indicating that three of these four test sites may be eliminated without sacrificing reliability

Non-equilibrium electronic transport and interaction in short metallic nanobridges

We have observed interaction effects in the differential conductance $G$ of short, disordered metal bridges in a well-controlled non-equilibrium situation, where the distribution function has a double Fermi step. A logarithmic scaling law is found both for the temperature and for the voltage dependence of $G$ in all samples. The absence of magnetic field dependence and the low dimensionality of our samples allow us to distinguish between several possible interaction effects, proposed recently in nanoscopic samples. The universal scaling curve is explained quantitatively by the theory of electron-electron interaction in diffusive metals, adapted to the present case, where the sample size is smaller than the thermal diffusion length.Comment: Published version, 6 Pages, 6 postscript figures, 1 tabl

Transport properties and point contact spectra of Ni_xNb_{1-x} metallic glasses

Bulk resistivity and point contact spectra of Ni_xNb_{1-x} metallic glasses have been investigated as functions of temperature (0.3-300K) and magnetic field (0-12T). Metallic glasses in this family undergo a superconducting phase transition determined by the Nb concentration. When superconductivity was suppressed by a strong magnetic field, both the bulk sample R(T) and the point contact differential resistance curves of Ni_xNb_{1-x} showed logarithmic behavior at low energies, which is explained by a strong electron - "two level system" coupling. We studied the temperature, magnetic field and contact resistance dependence of Ni_{44}Nb_{56} point-contact spectra in the superconducting state and found telegraph-like fluctuations superimposed on superconducting characteristics. These R(V) characteristics are extremely sensitive detectors for slow relaxing "two level system" motion.Comment: 4 pages, 5 figure

Shot Noise by Quantum Scattering in Chaotic Cavities

We have experimentally studied shot noise of chaotic cavities defined by two quantum point contacts in series. The cavity noise is determined as 1/4*2e|I| in agreement with theory and can be well distinguished from other contributions to noise generated at the contacts. Subsequently, we have found that cavity noise decreases if one of the contacts is further opened and reaches nearly zero for a highly asymmetric cavity.Comment: 4 pages, 4 figures, REVTe

Evidence for saturation of channel transmission from conductance fluctuations in atomic-size point contacts

The conductance of atomic size contacts has a small, random, voltage dependent component analogous to conductance fluctuations observed in diffusive wires (UCF). A new effect is observed in gold contacts, consisting of a marked suppression of these fluctuations when the conductance of the contact is close to integer multiples of the conductance quantum. Using a model based on the Landauer-Buettiker formalism we interpret this effect as evidence that the conductance tends to be built up from fully transmitted (i.e., saturated) channels plus a single, which is partially transmitted.Comment: An error in Eq.(2) was corrected, where a square root was added to the factor (1-cos(gamma)). This results in a revised estimate for the mean free path of 5 nm, which is now fully consistent with the estimates from the series resistance and the thermopowe

Magnetic field effects in energy relaxation mediated by Kondo impurities

We study the energy distribution function of quasiparticles in voltage biased mesoscopic wires in presence of magnetic impurities and applied magnetic field. The system is described by a Boltzmann equation where the collision integral is determined by coupling to spin 1/2 impurities. We derive an effective coupling to a dissipative spin system which is valid well above Kondo temperature in equilibrium or for sufficiently smeared distribution functions in non-equilibrium. For low magnetic field an enhancement of energy relaxation is found whereas for larger magnetic fields the energy relaxation decreases again meeting qualitatively the experimental findings by Anthore et al. (cond-mat/0109297). This gives a strong indication that magnetic impurities are in fact responsible for the enhanced energy relaxation in copper wires. The quantitative comparison, however, shows strong deviations for energy relaxation with small energy transfer whereas the large energy transfer regime is in agreement with our findings.Comment: 14 pages, 8 figure

Nonlinear voltage dependence of the shot noise in mesoscopic degenerate conductors with strong electron-electron scattering

It is shown that measurements of zero-frequency shot-noise can provide information on electron-electron interaction, because the strong interaction results in the nonlinear voltage dependence of the shot noise in metallic wires. This is due to the fact that the Wiedemann-Franz law is no longer valid in the case of considerable electron-electron interaction. The deviations from this law increase the noise power and make it dependent strongly on the ratio of electron-electron and electron-impurity scattering rates.Comment: 4 pages, 2 figures, revised version according to referee's comment

Reactions of a Be-10 beam on proton and deuteron targets

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus Be-11 has been examined through the 10Be(d,p) reaction in inverse kinematics at equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of Be-10 on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of Be-10 on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in Be-11 were analyzed using the Finite Range ADiabatic Wave Approximation (FR-ADWA). Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4) respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor.Comment: 16 Pages, 10 figure