[seminar] Seminar Fizičkog odsjeka, Zawadowski

[hbuljan at phy.hr]

Poštovani kolege,

    u četvrtak 21. 09., s početkom u 14:15 sati, Prof. Alfred Zawadowski
sa Sveučilišta u Budimpešti održati će predavanje naslovljeno
"Energy relaxation due to magnetic impurities in mesoscopic
wires: Logarithmic approach". Predavanje će se održati u
predavaonici F102 na Fizičkom odsjeku PMF-a. Dodatne informacije
o predavanju nalaze se u nastavku poruke.

Srdačan pozdrav
Hrvoje Buljan

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SEMINAR FIZIČKOG ODSJEKA
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Vrijeme:  četvrtak, 21. 09. 2006., 14:15 sati (točno)
Mjesto:   Fizički odsjek, Bijenička c. 32, predavaonica F102


     ENERGY RELAXATION DUE TO MAGNETIC IMPURITIES IN
          MESOSCOPIC WIRES: LOGARITHMIC APPROACH

                Prof. Dr. Alfred Zawadowski

       Budapest University of Technology and Economics,
    Institute of Physics and Research Group Theory of Condensed Matter
         of Hungarian Academy of Sciences, Budapest, Hungary


The transport in mesoscopic wires with large applied bias voltage
has recently attracted great interest by measuring the energy
distribution of the electrons at a given point of the wire, in Saclay. In
the previous theoretical works of different authors extensive
numerical calculations were presented, but the relative importance of the
different effects was hidden. The main goal of the present
talk is to break up the calculation and show how the final result is
formed step by step. In the diffusive limit with negligible
energy relaxation the energy distribution shows two sharp steps at the
Fermi energies of the two contacts. Those steps are, however,
broadened due to the energy relaxation which is relatively weak if only a
Coulomb electron-electron interaction is assumed. In some of the
experiments the broadening is more essential, reflecting an
anomalous energy relaxation rate proportional to E-2 instead of E-3/2
where E is the energy transfer. Later it has been suggested that such a
relaxation rate can be due to the electron-electron interaction
mediated by Kondo impurities which is, as has been known for a long time,
singular in E. In the present paper the magnetic-impurity-mediated
interaction is systematically studied in the logarithmic approximation
valid above the Kondo temperature. In the case of large applied bias
voltage Kondo resonances are formed at the steps of the distribution
function and they are narrowed by increasing the bias. An additional
Korringa energy broadening occurs for the spins by creating electron-hole
pairs in the electron gas out of equilibrium. That smears the Kondo
resonances, and the renormalized coupling can be replaced by a smooth but
essentially enhanced average coupling and that enhancement can reach the
value 8-10. Thus the experimental data can be described by formulas
without logarithmic Kondo corrections, but with enhanced coupling. In
certain regions of large bias, that averaged coupling depends weakly on
the bias. In those cases the distribution function depends only on the
ratio of the electron energy and the bias, showing scaling behavior.

- O. Újsághy, A. Jakovác and A. Zawadowski,
  Phys. Rev. B 72, 205119 (2005)

		          Voditelj seminara FO
		          Hrvoje Buljan, hbuljan at phy.hr

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