Dr. Jiejuan Yan [Jilin University, China]

Title: The Structural and Electrical Transport Properties of Compressed AlAs, SnSe, and GeTe

Time: 10:00 - 11:00 AM, Monday, May 9, 2016

Place: Conference Room 201, Building 6, HPSTAR (Shanghai)

Host: Dr. Hengzhong Zhang

Abstract:

Selenide tin (SnSe) and Telluride germanium (GeTe) have been attracted considerable experimental and theoretical efforts due to their unique properties, including topological insulating states and high thermoelectric performance. High pressure has been shown to be an effective approach to modulate the electronic structure of materials, and subsequently the electrical transport parameters of materials. An important issue concerns how compression tunes the topological insulating states.  Besides, can the thermoelectric performance (ZT= (S2σ/κ)T) be improved by the compression-driven enhancement of electrical conductivity? Furthermore, exploring the metallic state with application of compression is a matter of interest in band-gap engineering. However, few studies can be found about the electrical transport properties of SnSe and GeTe under compression. We evaluated the electrical resistivity measurements to explore the high-pressure metallic behavior of SnSe and GeTe. The experimental results indicate that SnSe transforms from a semiconducting to semimetallic state at 12.6 GPa. GeTe behaves as a metal in all pressure range. Hall-effect measurements further explore the mechanism behind the abnormal variations. Meanwhile, First-principles calculations and XRD measurements were also carried out for better understanding the variations of electrical transport properties.

References:

1. J. J. Yan et al., Electrical Transport Properties of AlAs under Compression: Reversible Boundary Effect, Phys.Chem.Chem.Phys., 2015, 17, 26277.

2. J. J. Yan et al., Pressure-driven semiconducting-semimetallic transition in SnSe, Phys.Chem.Chem.Phys., 2016, 18, 5012.

3. T. J. Ou, J. J. Yan et al., Nanoscale, 2016.

4. L. Wang, F. Ke, Q. L. Wang, J. J. Yan et al., Appl. Phys. Lett., 2015, 107, 201603.

Biography of the Speaker:

Jiejuan Yan completed her Ph.D study under the supervision by Prof. Chunxiao Gao in State Key Lab of Superhard Materials, Institute of Atomic and Molecular Physics, Jilin University. She mainly focused on the electrical transport properties of semiconductor materials under high pressure. Her work on AlAs, SnSe, and GeTe discussed the physical mechanism of the phase transition and electrical transport properties. In addition, she has studied the connection between the phase transitions and the transport properties.

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题目：高压下AlAs、SnSe及 GeTe的结构和电输运性质研究

摘要：

SnSe 和GeTe由于它们具有很多卓越的物理性质，包括：拓扑绝缘性和高的热电性能等，而受到人们在实验和理论方面的广泛研究。压力作为一维调节材料电子结构进而调节电输运参数的有效手段，其如何调节材料的拓扑绝缘性成为一个重要的课题。而能否通过压力提高材料的导电性从而提高其ZT= (S2σ/κ)T对人们寻找高性能的热电材料具有重要意义。此外，探索压力作用下材料的金属态是带隙工程中人们感兴趣的课题。然而高压下SnSe 和GeTe的电输运性质研究仍然很少。我们对SnSe 和GeTe进行了电阻率测量探究其高压金属特性。研究结果表明，在12.6 GPa，SnSe从半导体传导特性转变为金属传导特性，而GeTe在所有的压力范围内均表现为金属传导特性。霍尔效应测量进一步研究了电输运性质的变化机制。同时，为了更好的理解SnSe 和GeTe的电输运性质我们对其进行了第一性原理计算及高压XRD测量研究。