Colloquium: Mohammad Hamidian
"Imaging Electrons in the Realm of Quantum Entanglement:
Visualizing the Formation of Heavy Fermions and the Impact of Kondo Holes"
Abstract: Heavy fermion materials are a realization of a system in which the starkly contrasting worlds of itinerant electrons and a matrix of localized magnetic moments become quantum mechanically entangled. This hybridization process has a direct manifestation on the macroscopic observables including thermodynamic quantities from which the term ‘heavy’ originally stems. While a great deal has been learned experimentally and theoretically about heavy fermions over the last 30 years, 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 entanglement 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. The introduction of an atomic-scale defect in this hybridized lattice by replacing a magnetic atom randomly with a non-magnetic atom is referred to as a Kondo Hole. The atomic scale electronic structure of a Kondo Hole, reported here for the first time, contains real-space modulations in the hybridization strength as recently predicted (Figgins et al arXiv 1010.3875). 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.
Refreshments will be served at 2:30 in 2214 SES