Oscillations of the magnetic polarization in a Kondo impurity at finite magnetic fields

The electronic properties of a Kondo impurity are investigated in a magnetic field using linear response theory. The distribution of electrical charge and magnetic polarization are calculated in real space. The (small) magnetic field does not change the charge distribution. However, it unmasks the Kondo cloud. The (equal) weight of the d-electron components with their magnetic moment up and down is shifted and the compensating s-electron clouds don't cancel any longer (a requirement for an experimental detection of the Kondo cloud). In addition to the net magnetic polarization of the conduction electrons an oscillating magnetic polarization with a period of half the Fermi wave length is observed. However, this oscillating magnetic polarization does not show the long range behavior of Rudermann-Kittel-Kasuya-Yosida oscillations because the oscillations don't extend beyond the Kondo radius. They represent an internal electronic structure of the Kondo impurity in a magnetic field. PACS: 75.20.Hr, 71.23.An, 71.27.+

Density of States in the Magnetic Ground State of the Friedel-Anderson Impurity

By applying a magnetic field whose Zeeman energy exceeds the Kondo energy by an order of magnitude the ground state of the Friedel-Anderson impurity is a magnetic state. In recent years the author introduced the Friedel Artificially Inserted Resonance (FAIR) method to investigate impurity properties. Within this FAIR approach the magnetic ground state is derived. Its full excitation spectrum and the composition of the excitations is calculated and numerically evaluated. From the excitation spectrum the electron density of states is calculated. Majority and minority d-resonances are obtained. The width of the resonances is about twice as wide as the mean field theory predicts. This broadening is due to the fact that any change of the occupation of the d-state in one spin band changes the eigenstates in the opposite spin band and causes transitions in both spin bands. This broadening reduces the height of the resonance curve and therefore the density of states by a factor of two. This yields an intuitive understanding for a previous result of the FAIR approach that the critical value of the Coulomb interaction for the formation of a magnetic moment is twice as large as the mean field theory predicts

KONDO RESISTIVITY IN COPPER-CHROMIUM AT 35 GHZ

L'impédance de surface pour une irradiation de micro-ondes a 35 GHz a été mesurée à des températures aussi basses que 80 mK pour des concentrations en chrome entre 30 et 150 ppm. A ces fréquences, (au refroidissement de l'alliage) on observe un net accroissement de la température correspondant à la saturation de la divergence "Kondo" en résistivité, par rapport à la valeur mesurée en résistivité statique.The microwave surface impedance at 35 GHz has been measured at temperatures down to 80 mK for chromium concentrations between 30 and 150 ppm. The temperature, at which the "Kondo" divergence in the resistivity saturates as the alloy is cooled, is shown to be strongly enhanced at these frequencies over its value for static resistivity