報告日期：2018年11月5日

報告時間：10:30

報 告 人：吳明衛(wèi) 教授（中國科技大學(xué)）

報告地點：長安校區(qū) 物理學(xué)與信息技術(shù)學(xué)院三層會議室（致知樓3328）

主辦單位：物理學(xué)與信息技術(shù)學(xué)院

報告人簡介：

吳明衛(wèi)教授，中國科學(xué)技術(shù)大學(xué)教授，1986年-1991年，中國科技大學(xué)近代物理系理論物理專業(yè)學(xué)士，1991年-1995年中國科技大學(xué)凝聚態(tài)物理博士，1995年12月-1996年8月美國Stevens技術(shù)所博士后，1996年9月-1997年8月美國Rochester大學(xué)博士后，1997年9月-1998年9月德國法蘭克福大學(xué)理論物理研究所博士后，1998年10月-2001年2月美國加利福尼亞大學(xué)Santa Barbara分校博士后。2001年2月-2001年12月任日本東京大學(xué)研究員，2000年11月至今，任中國科技大學(xué)教授。2002年8月起擔(dān)任西藏大學(xué)數(shù)理系客座教授，2003年2月-4月到美國Delaware大學(xué)訪問，2004年至今任合肥微尺度物質(zhì)科學(xué)國家實驗室研究員，目前擔(dān)任Physica E、Journal of Superconductivity and Novel Magnetism等雜志的編輯和編委。吳明衛(wèi)教授的主要研究領(lǐng)域為凝聚態(tài)理論，主要的研究興趣涉及自旋電子學(xué)、超導(dǎo)動力學(xué)、半導(dǎo)體超快光譜學(xué)、熱電子輸運以及導(dǎo)電聚合物中激子和非線性光學(xué)性質(zhì)，有機材料中的輸運性質(zhì)理論等。

報告摘要：

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 v_s is larger than a threshold v_L=|Δ|/k_F. 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 v_s < v_L with only the nonviscous superfluid, the Meissner supercurrent is excited and the gap equation can be reduced to the Ginzburg-Landau equation. At v_s ≥ v_L, 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 v_s < v_L, only the nonviscous superfluid is present, whereas at v_s ≥ v_L, 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.