SEMINAR The State Key Lab of High Performance Ceramics and Superfine Microstructure Shanghai Institute of Ceramics, Chinese Academy of Sciences 中 国 科 学 院 上 海 硅 酸 盐 研 究 所 高 性 能 陶 瓷 和 超 微 结 构 国 家 重 点 实 验 室 Recent development in phase change memory materials using time-dependent density functional theory Shengbai Zhang Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA 时间：2018年6月4日（星期一）上午9:30 地点：嘉定园区F楼8（2）会议室 欢迎广大科研人员和研究生参与讨论！ 联系人：孙宜阳（15618031025） 报告摘要： Phase change memory (PCM) materials exhibit fascinating physics as SET (i.e., its amorphiszation) happens in less than a 100 fs, while RESET (i.e., its recrystallization) happens in a matter of only a few ns, which defies exclusively all the phase-change phenomena known for solid state. They are the backbone of DVD, as well as that of electronic memory devices such as IBM’s storage class memory and the recent Micron’s X-Point technology. Most recently, PCM also gained momentum for developing non-von Neumann architecture, beyond CMOS, and in-memory computing. Our journey on the quest of the PCM materials started with the understanding of phase transitions using static and quasi-static first-principles calculations. Nonetheless, a non-thermal nature of the ultrafast PCM material amorphization under a high electronic excitation was unveiled for the first time, which has since gained considerable momentum. Using the recently developed time-dependent density functional theory (TDDFT)-molecular dynamics (MD), we not only confirmed the previous predictions, but also uncovered the dependence on the excitation energies – a high enough excitation energy inevitably leads to a significant carrier multiplication effect. As such, a phase transition takes place well before the lattice can be heated up. A similar phenomenon found in standard semiconductors, coined with the name plasma quenching, was also explained by our theory. Most recently, we found that, in ferroelectric materials, an equally ultrafast (< a few 100’s fs) phases transition can take place between crystalline phases. While this proposition is in startle contrast to our na？ve intuition, it is in full agreement with experiments. 主讲人简介: Shengbai Zhang graduated from Jilin University in 1982. He received Ph.D. in Physics from the University of California at Berkeley in 1989. He moved to Xerox PARC as a postdoc, before joining the National Renewable Energy Laboratory in 1991. In 2008, he became the Senior Kodosky Constellation Chair and Professor in Physics at Rensselaer Polytechnic Institute. His computational research covers a wide range of materials for bulk properties, defect structures, and surface physics. His recent work involves emerging low-cost photovoltaic materials, phase change memory materials, topological insulators, Weyl semimetals, two-dimensional layered materials, and excited state dynamics. He has published ~390 peer-reviewed articles, including 60 in Physical Review Letters, with a total citation over 25,000. He is a Fellow of the American Physical Society since 2001. |
