报告日期：2018年11月5日
报告时间：10:30
报 告 人：吴明卫 教授（中国科技大学）
报告地点：长安校区 物理学与信息技术学院三层会议室（致知楼3328）
主办单位：物理学与信息技术学院
报告人简介：
吴明卫教授，中国科学技术大学教授，1986年-1991年，中国科技大学近代物理系理论物理专业学士，1991年-1995年中国科技大学凝聚态物理博士，1995年12月-1996年8月美国Stevens技术所博士后，1996年9月-1997年8月美国Rochester大学博士后，1997年9月-1998年9月德国法兰克福大学理论物理研究所博士后，1998年10月-2001年2月美国加利福尼亚大学Santa Barbara分校博士后。2001年2月-2001年12月任日本东京大学研究员，2000年11月至今，任中国科技大学教授。2002年8月起担任西藏大学数理系客座教授，2003年2月-4月到美国Delaware大学访问，2004年至今任合肥微尺度物质科学国家实验室研究员，目前担任Physica E、Journal of Superconductivity and Novel Magnetism等杂志的编辑和编委。吴明卫教授的主要研究领域为凝聚态理论，主要的研究兴趣涉及自旋电子学、超导动力学、半导体超快光谱学、热电子输运以及导电聚合物中激子和非线性光学性质，有机材料中的输运性质理论等。
报告摘要：
Within a gauge-invariant microscopic kinetic theory, we study the electromagnetic response in the superconducting states. Both superfluid and normal-fluid dynamics are involved. We predict that the normal fluid is present only when the excited superconducting velocity vs is larger than a threshold vL=|Δ|/kF. Interestingly, with the normal fluid, we find that there exists friction between the normal-fluid and superfluid currents. Due to this friction, part of the superfluid becomes viscous. Therefore a three-fluid model, normal fluid and nonviscous and viscous superfluids, is proposed. For the stationary magnetic response, at vs < vL with only the nonviscous superfluid, the Meissner supercurrent is excited and the gap equation can be reduced to the Ginzburg-Landau equation. At vs ≥ vL, with the normal fluid and nonviscous and viscous superfluids, in addition to the directly excited Meissner supercurrent in the superfluid, a normal-fluid current is also induced through the friction drag with the viscous superfluid current. Due to the normal-fluid and viscous-superfluid currents, the penetration depth is influenced by the scattering effect. In addition, a modified Ginzburg-Landau equation is proposed. We predict an exotic phase in which both the resistivity and superconducting gap are finite. As for the optical response, the excited vs oscillates with time. When vs < vL, only the nonviscous superfluid is present, whereas at vs ≥ vL, normal fluid and nonviscous and viscous superfluids are present. We show that the excited normal-fluid current exhibits the Drude-model behavior, while the superfluid current consists of the Meissner supercurrent and Bogoliubov quasiparticle current. Due to the friction between the superfluid and normal-fluid currents, the optical conductivity is captured by the three-fluid model. Finally, we also study the optical excitation of the Higgs mode. By comparing the contributions from the drive and Anderson-pseudospin pump effects, we find that the drive effect is dominant at finite temperature whereas at zero temperature, both effects contribute.
