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Dr. Jong-Soo Rhyee

Dept. of Applied Physics, Kyung Hee University Gihung-gu, Korea


Talk Title
Enhancement of thermoelectric performance in the vicinity of topological phase transition in topological crystal insulator and Dirac semimetal

Talk Abstract

Topological insulators generally share commonalities with good thermoelectric materials because of their narrow band gaps and heavy constituent elements. Here we propose that a topological crystalline insulator (TCI) and Dirac semimetal could exhibit a high thermoelectric performance by breaking its crystalline symmetry and tuning chemical potential by elemental doping. As a candidate material, we investigate thermoelectric properties of the Cl-doped topological crystalline insulator Pb0.7Sn0.3Se. The infrared absorption spectra reveal that the band gap is increased from 0.055 eV for Pb0.7Sn0.3Se to 0.075 eV for Pb0.7Sn0.3Se0.99Cl0.01, confirming that the Cl-doping can break the crystalline mirror symmetry of a topological crystalline insulator Pb0.7Sn0.3Se and thereby enlarges its bulk electronic band gap. The topological band inversion is confirmed by the extended X-ray absorption fine structure spectroscopy (EXAFS) showing that the TCI state is weakened in chlorine x = 0.05 doped compound. The small gap opening and partial linear band dispersion with massless and massive bands may have high power factor for high electrical conductivity with enhancement of Seebeck coefficient. As a result, the Pb0.7Sn0.3Se0.99Cl0.01 shows a considerably enhanced ZT value compared to that of the undoped Pb0.7Sn0.3Se. This work demonstrates that the optimal n-type Cl-doping tunes the chemical potential together with breaking the state of topological crystalline insulator, suppresses a bipolar conduction at high temperatures, and thereby enables the Seebeck coefficient to keep increasing up to 823 K, resulting in a significantly enhanced power factor at high temperatures. In addition, the bipolar contribution to thermal conductivity is effectively suppressed for the Cl-doped samples of Pb0.7Sn0.3Se1-xClx (x ≥ 0.01). We propose that breaking the crystalline mirror symmetry in topological crystalline insulators could be a new research direction for exploring high performance thermoelectric materials.

Short Biography

Prof. Jong-Soo Rhyee obtained Ph.D from the Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST) at 2005. After a post-doctoral researcher at the Max-Plank-Institute for Solid State Research in Stuttgart, Germany, he became a R&D Staff researcher in Samsung Advanced Institute of Technology, Korea (2007~2010). Now, he is an associate professor of Dept. of Applied Physics and vice dean of the College of Applied Sciences of Kyung Hee University in Korea. His research interest covers the synthesis and fundamental understanding of thermoelectric, magnetic, and superconducting materials. Especially, his previous and current research topics include high thermoelectric performance in the intrinsic low dimensionality, fundamental understanding and enhancement of thermoelectric performance in topologically protected system, 2-dimensional transition metal dichalcogenide (TMDC) and their misfit-layered superlattice compounds, and unconventional superconductivity in various materials system. Up to now, he published 94 SCI papers (since 2002) with the 1009 number of paper citation during recent 5 years (since 2013) (Google scholar). He got IAAM Scientist Medal from the International Association of Advanced Materials (February 2018), 2017 Outstanding Research Achievement Award from Kyung Hee University, TJ Park Junior Faculty Fellowship from the POSCO TJ Park Foundation (October 2011), Bombi Physics Award from the Korean Physical Society (April 2010), Young Investigator Award from the International Thermoelectric Society (ITS, July 2009) etc.

Talk Keywords
Thermoelectric, Topological insulator, Dirac semimetal, Topological phase transition, ZT.
Target Audience
Stuents, academica, industry, government, NGOs
Speaker-intro video

The International Conference on Innovative Applied Energy (IAPE’18)