The innovation engine for new materials

Visualizing Individual Kondo Holes: Textures in the Pond of Strong Correlations

Seminar Group: 


Dr. Mohammad H. Hamidian


Physics Dept.
Cornell University


Friday, October 12, 2012 - 10:00am


MRL Room 2048


Prof. James Allen

The presence of dopants in strongly correlated systems can lead to substantial alterations in the electronic structure and consequently the macroscopic observables. However, the microscopic spatial reorganizations underlying the macroscopic manifestations are rarely directly measured. This leads to a crucial question as to how the defects' presence truly alters the properties of the system. For example, are the changes dominantly local or do the defects' presence have much longer range correlations and to what extent are their collective effects relevant in shaping the macroscopic quantities? Studied for decades, Kondo Hole defects, arising when a magnetic atom in a heavy fermion compound is replaced by a non-magnetic one, lead to changes in the thermodynamic and transport properties in both the heavy Fermi liquid and superconducting states. The inferred disorder effects arising from Kondo Holes have centered on the long standing premise of local disturbances in the heavy fermion background, as in a 'Swiss Cheese' model.

In this talk I will begin by presenting 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)). Having established the heavy fermion background I will report the first visualization of the atomic scale electronic structure of a Kondo Hole and directly show that in contrast to a purely localized restructuring of the electronic environment, Kondo Holes generate a long-range spatial texture on a fundamental energy scale of electron-electron correlations (Hamidian, Schmidt, et al., PNAS 108, 18233 (2011)). By developing the "hybridization gapmap" technique, the inferred inhomogeneity effects from macroscopic observables can now be associated with the interference patterns of real space modulations of the heavy fermion hybridization strength generated by a random distribution of Kondo Holes. Consequently, these observations provide a new perspective on how spatial inhomogeneity may arise in a wide range of strongly correlated systems.