The 369th forum: An STM view on correlated electron systems: from heavy fermion metals to topological Kondo insulators
Max Planck Institute for Chemical Physics of Solids
Dr. Steffen Wirth received his Ph.D. degree in Physics at Technical University Dresden, Germany in 1995. Then he did his postdoctoral research at Trinity College during 1995-1996 and Florida State University during 1996-2000, when he received the Feodor Lynen fellowship from the Humboldt-foundation. In 2010, he became a scientific staff member at Max Planck Institute (MPI) for Chemical Physics of Solids, Dresden. He worked as a visiting professor at the University Gottingen in 2009-2010. In 2010, he became an associate professor and research group leader at MPI for Chemical Physics of Solids. He was elected to be a fellow of American Physical Society in 2017.
Dr. Wirth is an expert in scanning tunneling microscopy, magnetization and electronic transport measurements at low temperatures and high magnetic fields. His research interest covers a broad range of topics in condensed matter physics, including magnetic materials, strongly correlated electron systems including heavy fermion metals, quantum criticality, superconductivity, electronic transport properties, Kondo insulators, topological materials, manganites, chalcogenides and magnetic nanoparticles.
Electronic correlations give rise to a plethora of interesting phenomena and phases. For example, hybridization between 4f and conduction electrons in heavy fermion metals may result in the generation of low-energy scales that can induce quantum criticality and unconventional superconductivity . One of the most important techniques that helped shaping our understanding of nonlocal correlations, both magnetic and superconducting, has been scanning tunneling spectroscopy (STS) with its unique ability to give local, microscopic information that directly relates to the one-particle Green's function. We combine STS with bulk measurements to obtain complementary information on different length scales. We compare hybridization effects as observed by STS, focusing on the model heavy fermion metal YbRh2Si2 and the intermediate-valence Kondo insulator SmB6. Investigation of high-quality single crystals of YbRh2Si2 allows to study the evolution the single-ion Kondo effect and lattice Kondo coherence upon lowering temperature . We also show how Kondo coherence connects with quantum criticality . Low-temperature in-situ cleaving of SmB6 single crystals mostly resulted in reconstructed surfaces, while non-reconstructed patches were found less frequently. The different surface terminations give rise to marked differences in the STS results ; in our analysis, however, we concentrate on STS of non-reconstructed areas. These spectra confirm the hybridization picture typically considered for this material . At the surface, the Kondo effect is suppressed to lower temperatures as compared to the bulk material . We show the development of the surface states at low temperatures and how it is locally suppressed around magnetic impurities . The latter is consistent with a topological nature of these surface states.
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