报告题目：2D monochalcogenides: from ferroelectricity to valleytronics

报  告  人：常凯，北京量子信息科学研究院，研究员

时        间：2021年4月15日  14:30

地        点：中心校区知新楼C座七层物理学院量子报告厅

邀  请  人：李洋洋 物理学院教授、博士生导师

摘要：

The scientific interests in 2D ferroic materials, which are potential building blocks for the next-generation fast, low-power cost and miniaturized non-volatile logic and memory devices, have experienced an explosion over the past few years. In this talk, I will introduce the discovery of robust ferroelectricity in 2D monochalcogenide films with staggered black phosphorus lattices, as well as the interesting electronic phenomena associated with their domain walls and spin-valley coupled band structures. Combining van der Waals molecular beam epitaxy (vdW-MBE) and variable temperature scanning tunneling microscopy (VT-STM), we revealed switchable in-plane spontaneous polarizations in monolayer SnTe and SnSe with transition temperatures T_c = 270 K and 380 K, respectively. Surprisingly, the T_c of monolayer SnTe is much higher than that in its bulk counterpart (~100 K), which is ascribed to a thickness-dependent phase transition. A non-volatile memory device based on 2D ferroelectrics with in-plane polarizations was proposed. We have also discovered band-bending-induced conductive domain walls and nanoplate edges in ultrathin SnTe films, which are promising for the fabrication of 1D logic devices. Between the parallel, electrically neutral 90° domain walls in monolayer SnTe, we have observed clear energetically dispersive electronic standing waves, which are found to be induced by a valley mismatch in k space, rather than high potential barriers at the 1D defects like the atomic steps on noble metal surfaces. Furthermore, applying quasiparticle interference technique, we have demonstrated a valley-dependent Zeeman-like spin splitting as large as 220 meV at the valence band maximum of monolayer Pb_0.5Sn_0.5Te. Intrinsic valley and spin Hall effects are expected in this noncentrosymmetric monolayer. In the end, I will briefly discuss the exciting future of 2D ferroic material heterostructures.

报告人简介：

常凯研究员，2009年本科毕业于山东大学物理学院，2015年博士毕业于清华大学物理系，师从著名量子材料专家薛其坤院士，2015-2019年在德国马克斯普朗克微结构物理研究所任博士后研究员，2019年年底回国加入北京量子信息科学研究院，任量子物态科学研究部低维量子材料团队PI。常凯研究员长期致力于高质量低维量子材料及其异质结的生长与扫描隧道显微学研究，发现并引领了IV-VI族二维铁电半导体的实验研究，在《Science》《Nature Physics》《Physical Review Letters》《Advanced Materials》等国际顶尖期刊上发表论文20余篇，总被引2000余次，H因子为12，受邀为物理学顶尖综述期刊《Reviews of Modern Physics》撰写Colloquium，有美国发明专利一项。常凯研究员目前正在北京量子院建设一个具备低维材料生长、原位原子与电子结构表征、微纳器件制备以及光学与光电子学表征能力的研究团队，未来的研究方向将集中于二维铁性材料异质结中的电子结构调控效应，为下游的量子计算、量子通信、量子精密测量等应用基础研究提供坚实的材料基础。

欢迎感兴趣的老师、同学参加！