报告摘要:
In ordinary superconductors, an external magnetic field is needed to generate magnetic vortices. We discuss two examples where this conventional folklore breaks down in a fundamental way. The first example is about superconductors with strong spin-orbit coupling. We show that topological defect excitations, dubbed quantum anomalous vortices (QAV), can nucleate around magnetic ions spontaneously in the absence of external magnetic fields. When such superconductors have a
nontrivial band structure and superconducting topological surface states, as do certain Fe-based superconductors, the magnetic impurity induced QAV are nonabelian and host Majorana zero mode (MZM) in the integer quantized vortex core states. Recent experimental observations of QAV and MZM will be discussed. The second example concerns the recently discovered kagome superconductorsAV3Sb5(A=K, Cs, Rb) that exhibit a cascade of correlated and topological quantum states triggered by an unconventional charge density wave (CDW) order. We discuss recent experimental evidence for time-reversal symmetry breaking in both the normal and the superconducting state. We argue that the essential phenomenology can be captured by a CDW with loop current order, realizable in models with extended Coulomb interactions on the kagome lattice. The loop-current Chern metal has a partially filled Chern band and Chern Fermi pockets carrying concentrated Berry curvature. We show how Cooper pairing over the Chern Fermi pockets produces an unprecedented roton superconductor, where the internal phases of three pairing components are locked at 120-degree and loop supercurrents circulate around an emergent vortex-antivortex lattice with pair density modulations. We discuss the extraordinary properties of this chiral topological superconductor and the experimental observation of fractionalized flux quantization and charge-6e superconductivity.
报告人简介：
汪自强，1984年毕业于清华大学，1989年获哥伦比亚大学物理学博士学位。他曾在罗格斯大学和洛斯阿拉莫斯国家实验室做博士后，1993年成为波士顿大学助理教授，目前是波士顿学院物理系教授，美国物理学会会士。他于1996年获得Cottrell学者奖，并于2021年获得SEED奖。汪自强教授发表论文200余篇，包括50多篇Physical Review Letters、40余篇Nature及Nature子刊。汪自强教授目前的研究重点是量子材料中的关联和拓扑电子态，包括非常规超导体、量子磁性、整数和分数量子反常霍尔系统、拓扑超导体以及其他奇异超导态。
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