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Visualizing Heavy Fermion Formation, and Their Destruction by Kondo Holes

While a great deal has been learned experimentally and theoretically about heavy fermions, some of the most fundamental microscopic tenets have remained experimentally unobserved. In this talk I will discuss spectroscopic imaging scanning tunneling spectroscopy (SI-STS) for direct visualization of heavy fermions. Using newly developed techniques for heavy quasiparticle interference imaging on the heavy fermion metal URu2Si2, the formation of the heavy fermion electronic structure both in momentum-space and real-space are imaged for the first time (Schmidt, Hamidian et al., Nature 465, 570 (2010)). The redistribution of spectral weight in the real space density of states as the hybridization process takes hold is accompanied by the splitting of a light hole-like band into two far heavier ones and consequently the opening of a direct hybridization gap. When a magnetic atom in a heavy fermion system is replaced by a non-magnetic atom, the result is a Kondo Hole. I will report the first visualization of the atomic scale electronic structure of a Kondo Hole, revealing the long-range real-space modulations in the hybridization strength that have been recently predicted (Hamidian, Schmidt et al., PNAS 108, 18233 (2011)). The random distribution of Kondo Holes also generates vivid hybridization disorder which can now be imaged by introducing the “hybridization gapmap” technique. These methods and observations open up a new frontier in the study and understanding of heavy fermion physics.