题目：ElectronicPhase Control with an Electric Field

报告人：袁洪涛  副研究员

                  斯坦福大学

时间：2015年9月1日（周二）10:00 a.m.

地点：国家脉冲强磁场科学中心B206

报告摘要：

Electric-field control of charge carrier density has attracted much attention since it is remarkably simple for modulating physical properties of condensed matters and for exploring new functionalities with a transistor configuration. To realize novel field-effect modulated electronic phenomena in solids, a broad range of attainable carrier density is always required. However, so far, owing to the limitation of dielectric breakdown in most solid dielectrics, the maximum carrier density accumulated in conventional field-effect transistors (FETs) is quite low (<< 1013 cm-2) and thus seriously limits the tunability of electronic states of solids, for example, not sufficient enough to induce insulator-to-superconductor transition. While, recently a new type of transistor, known as electric-double-layer transistor (EDLT), with ionic liquids (ILs) as gate dielectrics have been proved to be able to effectively attain a high carrier density up to levels of around 1015 cm-2 and to realize a large local electric field up to 50mV/cm at liquid/solid interfaces, which are attracting increasing interests because of their potential to greatly tune electronic states and even to create novel states of matter which are impossible or difficult to obtain in conventional methods.

In this presentation, I will discuss the interfacial carrier accumulation within liquid gated EDLTs and their novel tunability of varied electronic phase transitions in oxides, chacogenides and Dirac materials like graphene and topological insulators. I will start with fundamentals of interface electrochemistry and charging mechanism in such fantastic liquid/solid EDL interfaces, for example the competation between electrochemistry charging and electrostatic charging, or the interfacial band alginment and band engineering confirmed with measuring working functions of different ILs by photoemmision spectroscopy (PES). Based on these investigations and by further taking great advantages of high carrier density at EDL interfaces (1015 cm-2), we successfully obtained electric-field-induced insulator-metal transition in ZnO and insulator-superconductor transition in SrTiO3, KTaO3 and ZrNCl. Also we achieved carrier-mediated room temperature ferromagnetism in diluted magnetic semiconductors and giant anomalous Hall effect in magnetically doped topological insulators through modulating the interfacial carrier accumulation. On the other hand, by taking the advantage of large local electric field (50MV/cm), spin-orbit interaction (SOI) and resulting spin splitting of energy band of 2D systems can be regulated with structure inversion asymmetry (SIA) originated from the interfacial band bending and large applied electric fields, and further be used for generating spin-polarized carriers in solids. With magetotransport measurment under liquid gating, I will discuss a field-effect-tuned SOI and a crossover from weak localization (WL) to weak antilocalization (WAL) in 2D systems based on layered chacogenides, WSe2 and SnSe2, and demonstrate the resulting giant Rashba-type and Zeeman-type energy spin splitting with tunable splitting energy in a broad regime of 10-120 meV by simply changing the applied bias, which is supposed to open a new direction of “spin manipulation with liquid” in “interface spintronics”.

References：

1. K. Ueno, et al. Nature Nanotechnology 6, 408-412 (2011).

2. H. T. Yuan, et al. Adv. Funct. Mater. 19, 1046-1053 (2009).

3. J. T. Ye, et al. Science, 338, 1193-1196 (2012).

4. H. T. Yuan, et al. Nature Physics 9, 563–569 (2013).

5. H. T. Yuan, et al. Nature Nanotechnology 9, 851–857 (2014).

6. H. T. Yuan, et al. Nature Nanotechnology 10, 707–713 (2015).

报告人简介：

袁洪涛副研究员于2003-2007年在中国科学院物理研究所薛其坤院士研究组从事表面界面物理相关的博士论文研究工作。2007年获得博士学位后，在日本东北大学岩佐义宏研究组从事新型液栅场效应晶体管的设计开发和低温电子输运的博士后研究工作。2010年随岩佐教授转至东京大学应用物理系，继续从事液栅场效应晶体管以及场效应诱导的物性调制，并被聘任为东京大学量子相电子研究中心助理教授。2012年至今在Stanford大学Cui Yi研究组和Harold Y. Hwang研究组作为Associate Staff Scientist从事二维量子体系物理特性的场效应调制。

袁洪涛副研究员是在新型场效应器件,奇异异质界面及相关低温物理输运研究领域中非常活跃的青年科学家，尤其在液栅场效应晶体管器件设计和低温电子输运方面有着原创性的研究成果。他的主要研究领域包括：利用在栅压条件下离子液体可在半导体和强关联材料体系表面形成高密度的电双层结构，实现了以离子液体作为介电绝缘材料的电双层场效应晶体管(Electric-Double-Layer Transistor)原型器件，并开发出与之相关联的独特的器件工艺以及液体固体界面电子输运测量技术，进一步扩展到多种有机无机半导体材料当中。利用在栅压条件下离子液体在半导体表面形成电双层结构，在多种半导体材料上实现高性能、低功耗、高导通的场效应晶体管，并发现并深入研究了在界面处发生的多种奇异的场效应诱导的物理现象,比如场效应诱导绝缘体超导相变，顺磁铁磁相变，Rashba/Zeeman自旋极化等。

袁洪涛副研究员发表文章50余篇，其中包括Science，Nature子刊和PNAS 11篇。

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