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【材料学院】学术报告七:Spin Effects in ParamagneticThermoelectric Materials

2019年03月14日

报告主题:Spin Effects in Paramagnetic Thermoelectric Materials

报告嘉宾:Daryoosh Vashaee教授(北卡罗莱纳州立大学

  间:2019314日(周下午2:30-3:30

  点:材料学院 B2-527会议室

报告摘要

While the progress in traditional thermoelectric materials research based on the engineering of the charge carriers and phonons characteristics is reaching a plateau, adding spin and spin wave to the picture offers new degrees of freedom for developing new materials with unprecedented thermoelectric properties. The effect of spin on thermoelectric properties is a non-trivial topic with many aspects. In particular, spin entropy in hopping systems, dilute Kondo systems due to the resonant interaction of the magnetic impurities with free electrons, and magnon electron drag in magnetically ordered systems have all resulted in enhancement of the thermopower. Another significant effect, although not yet theoretically confirmed, is the paramagnon drag. Paramagnon drag has been experimentally observed in many paramagnetic spin fluctuation systems such as (Sc,Lu,Y)Co2 or UAl2 near their spin fluctuation temperatures. MnTe, a semiconducting A-type antiferromagnet, shows a robust magnon-electron drag near and below the Neel temperature. Interestingly, as we will show, this rather large enhancement of the thermopower did not diminish above the Neel temperature (~305K) and remained consistently high up to ~1000K (our highest measurement temperature). We will discuss several possible explanations of the observed large thermopower above the ordering temperature. Although spin entropy, magnon drag, and paramagnon drag have already shown zT enhancement in several materials, this is the first time that such effects lead to zT>1. A better understanding of the thermopower in the paramagnetic phase of MnTe can guide the development of higher performance thermoelectric materials which are not limited to the trade-off between the electrical conductivity and the thermopower.

报告人简介

Daryoosh Vashaee is an Associate Professor at North Carolina State University Electrical & Computer Engineering Department and Materials Science & Engineering Department. He received his Ph.D. working under the supervision of Dr. Ali Shakouri at University of California at Santa Cruz in 2004, worked at MIT as a postdoctoral scholar under the supervision of Drs. Mildred Dresselhaus and Gang Chen, and worked at Oklahoma State University as Assistant Professor in 2008-2013. He is an expert in the quantum and nanostructured materials for energy conversion and information technologies. In the past, he has contributed to the development of several key thermoelectric structures including heterostructure thermionic devices and bulk nanocomposite thermoelectric materials. He is the director of the Nanoscience and Quantum Engineering Research group at NC State University and leads the thermoelectric materials research in ASSIST, an NSF Engineering Research Center which is working on the development of self-powered wearable health and environmental monitoring and advising systems.

 

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