Electron-phonon scattering in quantum point contacts

We study the negative correction to the quantized value 2e(2)/h of the conductance of a quantum point contact due to the backscattering of electrons by acoustic phonons. The correction shows activated temperature dependence and also gives rise to a zero-bias anomaly in conductance. Our results are in qualitative agreement with recent experiments studying the 0.7 feature in the conductance of quantum point contacts.     

Temperature dependence of mobility in scattering on point defects

Scattering amplitude in the field of a short-range force center is calculated using factorization of the potential. The results obtained are used to study the temperature dependence of charge-carrier mobility in the random field of chaotically distributed structural point defects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 50–57, September, 1985.In conclusion, the author sincerely thanks V. L. Bonch-Burevich for his interest in the study and most valuable discussions.     

Temperature dependence of conductance and thermopower anomalies of quantum point contacts

It has been shown within the Landauer approach that the presence of the 0.7 anomaly in the conductance of a ballistic microcontact and the respective plateau in the thermopower implies pinning of the potential barrier height at a depth of k _B T below the Fermi level. A simple way of taking into account the effect of electron-electron interaction on the profile and temperature dependence of a smooth one-dimensional potential barrier in the lower subband of the microcontact has been proposed. The calculated temperature dependences of the conductance and Seebeck coefficient agree with the experimental gate-voltage dependences, including the emergence of anomalous plateaus with an increase in temperature.     

Kondo scattering from Yb in Mg-Yb alloys

We present low temperature electrical resistivity measurements on dilute alloys of Yb in Mg which cover the concentration range 0.021–1.16 at.% Yb. The results of the resistivity measurements of the alloys show weak but unambiguously Kondo-like minima contrary to pure Mg.     

Temperature dependence of a single Kondo impurity

Recent advances in scanning tunneling microscopy have allowed the observation of the Kondo effect for individual magnetic atoms. One hallmark of the Kondo effect is a strong temperature-induced broadening of the Kondo resonance. In order to test this prediction for individual impurities, we have investigated the temperature dependent electronic structure of isolated Ti atoms on Ag(100). We find that the Kondo resonance is strongly broadened in the temperature range T = 6.8 K to T = 49.0 K. These results are in good agreement with theoretical predictions for Kondo impurities in the Fermi liquid regime, and confirm the role of electron-electron scattering as the main thermal broadening mechanism.     

Superconducting quantum point contacts

We review our experiments on the electronic transport properties of atomic contacts between metallic electrodes, in particular superconducting ones. Despite ignorance of the exact atomic configuration, these ultimate quantum point contacts can be manipulated and well characterized in-situ. They allow performing fundamental tests of the scattering theory of quantum transport. In particular, we discuss the case of the Josephson effect.     

Locally critical point in an anisotropic Kondo lattice

We report the first numerical identification of a locally quantum critical point at which the criticality of the local Kondo physics is embedded in that associated with a magnetic ordering. We are able to numerically access the quantum critical behavior by focusing on a Kondo-lattice model with Ising anisotropy. We also establish that the critical exponent for the q-dependent dynamical spin susceptibility is fractional and compares well with the experimental value for heavy fermions.     

Slow two-level systems in point contacts

A great variety of experiments, like heat release measurements, acoustic measurements, and transport measurements on mesoscopic samples, have proved that two-level systems (TLSs) play a crucial role in the low-temperature thermal and electric properties of disordered systems. This paper is aimed at reviewing the role of slow TLSs in point contacts. First the theory of point contacts is summarized, concentrating on the discussion of different point-contact models, and on the different regimes of electron flow in the contact, mainly focusing on the ballistic and diffusive limit. The Boltzmann equation is solved in both regimes, and the position dependence of the electrical potential is determined. Then the scattering processes in point contacts are investigated, particularly concentrating on the scattering on slow TLSs. If the electron-assisted transitions between the two states are negligible the electron–two-level system interaction can be treated with a simplified Hamiltonian. The scattering on such slow TLSs causes non-linearity in the current–voltage characteristics of the point contact, which can be determined using Fermi's Golden Rule. These calculations are presented showing both the contribution of elastic and inelastic scattering, and including the dependence on the position of the TLS, and on the effect of high-frequency irradiation. These results are used to discuss the differences between these slow TLSs and the fast centres which may be described by the two-channel Kondo model. The available experimental results are analysed, distinguishing between the effects due to the different types of TLSs.