Towards artificial Kondo nano-lattice structures

近藤效应是关联电子系统物理学的一个主要例子。一般来说，它是与费米子浴耦合的局域简并屏蔽的结果。在狭义上，近藤效应指的是在传导电子系统中嵌入磁性杂质时，在低于近藤特征温度下形成自旋单线态。一个重要的未决问题涉及与近藤效应相关的特征长度尺度的性质。这种特征长度尺度或近藤屏蔽长度可以从与单态形成相关的电子能量增益和传导电子的费米速度来估计。理论估计发现，它是在10至1000 nm的范围内的金属Kondo systems.In这个项目的第一步将采取系统的研究的性质的Kondo屏蔽云及其相关的长度尺度在纳米级金属Kondo系统。其中一种方法是结合区域选择性原子层沉积和聚焦电子束诱导沉积（FEBID）技术制备基于近藤铂铬体系的金属近藤单电子晶体管（SET）。金属近藤SETs的低温电流-电压特性将揭示近藤屏蔽云的形成是否受到有限尺寸重整化效应的影响。第二种方法使用由FEBID制备的纳米颗粒金属，其中金属纳米颗粒掺杂有磁性杂质，以形成颗粒状近藤金属的新型材料类别。可以预期纳米晶粒之间的隧穿在低温下并且对于足够大的隧穿速率变得相干，使得形成相干的粒状费米液体，如在强隧穿耦合机制中的常规纳米粒状金属结构中所发现的。主要的科学相关性将是理解与从一大类金属间Ce，Yb或U化合物中已知的相干重费米子态相比的相似性和差异性。

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.