Towards artificial Kondo nano-lattice structures

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The Kondo effect is a prime example for the physics of correlated electron systems. In general terms, it is the result of the screening of a localized degeneracy coupled to a bath of fermions. In the narrower sense, the Kondo effect involves the formation of a spin singlet below a characteristic Kondo temperature if a magnetic impurity is embedded in a system of conduction electrons.An important open question relates to the nature of the characteristic length scale associated with the Kondo effect. This characteristic length scale or Kondo screening length can be estimated from the electronic energy gain associated with the singlet formation and the Fermi velocity of the conduction electrons. Theoretical estimates find it to be in the range from 10 to 1000 nm for metallic Kondo systems.In this project first steps will be taken towards a systematic study of the nature of the Kondo screening cloud and its associated length scale in nanoscale metallic Kondo systems. For this two complementary approaches are followed.In one approach, metallic Kondo single electron transistors (SET) based on the Kondo system Platinum-Chromium will be fabricated by combining area-selective atomic layer deposition and focused electron beam induced deposition (FEBID). The temperature- dependent low-temperature current-voltage characteristics of the metallic Kondo SETs will shed light on the question whether the formation of a Kondo screening cloud is subject to finite-size renormalization effects.The second approach uses nano-granular metals prepared by FEBID in which metallic nano-grains are dopend with magnetic impurities such as to form the novel material class of granular Kondo metals. Tunneling between the nano-grains may be expected to become coherent at low temperatures and for sufficiently large tunneling rates, such that a coherent, granular Fermi liquid is formed, as has been found in conventional nano- granular metal structures in the strong tunnel coupling regime. Of major scientific relevance will be to understand what the similarities and differences are in comparison with the coherent heavy fermion state known from a large class of intermetallic Ce, Yb or U compounds.