Seminar：An STM view on correlated electron systems: From heavy fermion metals to topological Kondo insulators

Steffen Wirth 

MPI for Chemical Physics of Solids Dresden, Germany

Time：10:00-11:00am, Monday, May 7，2018

Location：Room 201, Teaching Building 12, Yuquan Campus, Zhejiang University

Abstract

Electronic correlations give rise to a plethora of interesting phenomena and phases. 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. In our analysis, 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.

 

About the speaker

Education

1985 – 1990 Study of physics at the Technical University Dresden , Germany

1990 – 1992 Research assistent at the Physical Institute of the College of Transportation Dresden (refounded as College for Technical Sciences and Economy, HTW Dresden)

1992 – 1995 Research fellow at the Institute for Solid State and Materials Research Dresden (IFW Dresden)

Employment

1995.10 –1996.04  post-doc with Prof. J.M.D. Coey (magnetism) at Trinity College Dublin, Ireland

1996.05 – 1996.10 Research fellow at the Institute for Solid State and Materials Research Dresden  

1996.11 – 2000.04  post-doc with Dr. S. von Molnár at MARTECH, Florida State University

2000.05 - presently research fellow at the Max Planck-Institute for the Chemical Physics of Solids in Dresden, Germany

since 2010 W2 position the Max Planck-Institute for the Chemical Physics of Solids in Dresden, Germany