Prof. Junqiao Wu | 吴军桥 [University of California, USA]

Title: Electrons that conduct electricity but not heat

Time: 10:00 - 11:00 AM, Wednesday, June 21, 2017

Place: Conference Room 410, HPSTAR (Shanghai)

Host: Dr. Charles Zeng

Abstract

In conventional metals, itinerant electrons transport heat proportionally to the amount of electricity they transport, a fact known as the Wiedemann-Franz (W-F) law which is a hallmark of Fermi liquids. The law is robust in nearly all metals, with modest violations observed in exotic materials but all at low temperatures. We recently discovered [Science 355, 371 (2017)] a drastic violation of the W-F law above room temperature, where the electronic contribution to thermal conductivity amounts to only 10% of what is expected from the W-F law. The breakdown of the W-F law was observed in metallic tungsten vanadium dioxide in the vicinity of its metal-insulator transition. Different from previously established mechanisms, the unusually low electronic thermal conductivity is a signature of the absence of quasiparticles in transport of a strongly correlated electron fluid where heat and charge diffuse separately and independently. On the basis of these materials, we developed a reprogrammable meta-canvas on which arbitrary meta-photonic devices can be written, erased and re-written. Using the meta-canvas, we demonstrate dynamic manipulation of optical waves for light propagation, polarization and reconstruction.

Biography of the Speaker:

Prof. Junqiao Wu received a BS from Fudan University and a MS from Peking University, China, both in physics. He obtained a PhD degree from the University of California, Berkeley, and did postdoctoral research in the Department of Chemistry at Harvard University. In 2006, he started his faculty appointment at UC Berkeley where he is now a Full Professor, as well as a faculty scientist at Lawrence Berkeley National Laboratory. He is also a PI in the Tsinghua-Berkeley Shenzhen Institute. His honors include the 29th Ross N. Tucker Memorial Award, the US-NSF Career Award, the US-DOE Early Career Award, the Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House, the Outstanding Alumni Award from Peking University China, and the Bakar Faculty Fellowship. The Wu group explores novel properties and applications of strongly correlated electron materials with reduced dimensions, and optoelectronic, thermal and thermoelectric properties of semiconductor alloys and interfaces. He has made ground-breaking contributions to development and understanding of narrow-bandgap nitride semiconductors, highly mismatched semiconductor alloys, defect physics of low-dimensional semiconductors, and thermal/thermoelectric physics of novel materials. He has published over 200 papers that have received over 15,000 citations. More information can be found at http://mse.berkeley.edu/~jwu