Topologically quantized response is one of the focal points of contemporary condensed matter physics. While it directly results in quantized response coefficients in quantum systems, there has been no notion of quantized response in classical systems thus far. This is because quantized response has always been connected to topology via linear response theory that assumes a quantum mechanical ground state. Yet, classical systems can carry arbitrarily amounts of energy in each mode, even while possessing the same number of measurable edge modes as their topological winding. In this work, we discover the totally new paradigm of quantized classical response, which is based on the spectral winding number in the complex spectral plane, rather than the winding of eigenstates in momentum space. Such quantized response is classical insofar as it applies to phenomenological non-Hermitian setting, arises from fundamental mathematical properties of the Green’s function, and shows up in steady-state response, without invoking a conventional linear response theory. Specifically, the ratio of the change in one quantity depicting signal amplification to the variation in one imaginary flux-like parameter is found to display fascinating plateaus, with their quantized values given by the spectral winding numbers as the topological invariants.
简 介：李林虎，2015年于中国科学院物理研究所取得理学博士，现为中山大学物理与天文学院副教授，博士生导师。主要从事拓扑量子物态的理论研究，围绕凝聚态系统及量子模拟系统，探索新奇的拓扑机制及其产生的物理现象。近期主要成果包括首次提出或发现高环绕数弗洛凯（Floquet）拓扑扭结半金属、非厄米复合高阶拓扑态、临界非厄米趋肤效应等多种拓扑物态及效应，及通过动力学特征刻画高阶拓扑物态的一般性理论等。在物理学领域国际权威期刊发表论文28篇（第一作者及通讯作者20篇），包括4篇Phys. Rev. Lett.，1篇Nat. Comm.，1篇Comm. Phys.，16篇Phys. Rev. A/B等，其中3篇论文入选ESI高被引论文；并受邀为本领域国际专著撰写一个章节。