Towards artificial Kondo nano-lattice structures

近藤效应是相关电子系统物理学的一个主要例子。一般来说，它是一个局域简并耦合到一群费米子的筛选结果。从狭义上讲，近藤效应涉及到如果磁性杂质嵌入到传导电子系统中，则在特征近藤温度以下形成自旋单重态。一个重要的开放性问题涉及到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筛选长度可以通过与单线态形成和传导电子的费米速度相关的电子能量增益来估计。理论估计发现，对于金属近藤系统，其范围在10到1000纳米之间。在这个项目中，第一步将采取系统研究近藤筛选云的性质及其在纳米级金属近藤系统中的相关长度尺度。为此，遵循两种互补的方法。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）制备基于近藤系统铂铬的金属近藤单电子晶体管（SET）。金属Kondo SETs的温度依赖性低温电流-电压特性将阐明Kondo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FEBID制备的纳米颗粒金属，其中金属纳米颗粒与磁性杂质（如磁性杂质）相沉积，形成颗粒状近藤金属的新型材料类别。在低温和足够大的隧道速率下，纳米颗粒之间的隧道可能会变得相干，从而形成相干的粒状费米液体，就像在强隧道耦合状态下的传统纳米颗粒金属结构中发现的那样。重要的科学意义将是了解与从一大类金属间化合物Ce， Yb或U中已知的相干重费米子态相比，它们的相似和不同之处。

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.