| Brief Bio of the Speaker | 杜瑞瑞现任北京大学物理学院讲席教授，国际量子材料中心主任。于2011年入选为国家高级专家，回国前任美国莱斯大学物理与天文系教授。杜瑞瑞毕业于复旦大学, 1990年获得美国伊利诺斯(香槟)物理学博士学位。 1990 至1994 年于普林斯顿大学与贝尔实验室进行博士后研究期间, 通过一系列原创和高难度的实验, 证实了在分数量子霍尔效应中存在新的准粒子，称为复合费米子, 并测量了该粒子的一系列物理性质。这些成果现公认为该领域的经典工作。这些实验工作改变了人们对于凝聚态系统中电子－电子相互作用的传统认识，具有深远的影响。杜瑞瑞教授一直从事凝聚态中低温量子输运实验研究，如量子霍尔效应和其他低维系统, 以及拓扑量子材料和拓扑量子计算的基础问题等, 长期以来做出了一系列具有重要国际影响的工作。1996 年获得Sloan 研究奖; 1997 获得海外华人物理学家协会OCPA 杰出研究奖; 2003 年被选为美国物理学会 Fellow。所领导的实验室在分数量子霍尔效应和拓扑材料研究方面居国际领先地位。到北京大学工作后的主要目标是在北大国际量子材料中心建立一支高水平的凝聚态实验研究团队, 并带领团队把北京大学低维体系量子输运研究总体上提升到国际一流水平。 |
Abstract | Electron–hole pairing can occur in a dilute semimetal, transforming the system into an excitonic insulator state in which a gap spontaneously appears at the Fermi surface, analogous to a Bardeen–Cooper–Schrieffer (BCS) superconductor. In this talk I will report optical spectroscopic and electronic transport evidence for the formation of an excitonic insulator gap in an inverted InAs/GaSb quantum-well system at low temperatures and dilute electron–hole densities. Terahertz transmission spectra exhibit two absorption lines that are quantitatively consistent with predictions from the pair-breaking excitation dispersion calculated based on the BCS gap equation. Low-temperature electronic transport measurements reveal a gap of ~2 meV (or ~25 K) with a critical temperature of ~10 K in the bulk, together with quantized edge conductance, suggesting the occurrence of a topological excitonic insulator phase. We will also mention the transport properties of the edge states, which suggest the occurrence of a novel helical Luttinger liquid. The unique applications of the hosting materials, InAs/GaAs and InAs/InGaSb, to topological Qubits via proximity-induced Majorana Fermions and Parafermions will be discussed. References 1. Ivan Knez et al, Evidence for Helical Edge Modes in Inverted InAs/GaSb Quantum Well, Phys. Rev. Lett. 107, 136603 (2011) 2. Lingjie Du at al, Evidence for a topological excitonic insulator in InAs/GaSb bilayers, Nature Commun. 8, 1971 (2017) 3. J. Stajic, Probing an excitonic insulator, Science 358, pp. 1552-1553 (2017) |
