准周期晶格中的临界局域拓扑绝缘体

Observation of topological phase with critical localization in a quasi-periodic lattice

安德森局域化,即由无序导致的体系波函数在空间的局域,是凝聚态物理中的重要现象.在此基础上,无序对体系输运及拓扑性质均有深刻影响,例如对拓扑材料输运性质起关键作用的边缘态会被足够强的无序破坏.而在近来发现的安德森拓扑绝缘体中,无序可以从拓扑平庸的体系中诱导出拓扑非平庸相.本文利用超冷原子动量晶格的实验技术,通过调控动量晶格中的对角和非对角准周期无序,观测到一种不同于安德森拓扑绝缘体的临界局域拓扑绝缘相.此前的理论研究表明,由于不同形式的无序相互竞争,该体系的波函数具有分形维度,奇异能谱统计等临界特性.本文作者利用动力学可观测量刻画了体系的局域和拓扑特性,得到了临界局域拓扑相存在的初步证据.实验为进一步研究相互作用下的多体临界局域态奠定了基础.

Disorder and localization have dramatic influence on the topological properties of a quantum system.While strong disorder can close the band gap thus depriving topological materials of topological features,disorder may also induce topology from trivial band structures,wherein topological invariants are shared by completely localized states.Here we experimentally investigate a fundamentally distinct scenario where topology is identified in a critically localized regime,with eigenstates neither fully extended nor completely localized.Adopting the technique of momentum-lattice engineering for ultracold atoms,we implement a one-dimensional,generalized Aubry-Andrémodel with both diagonal and off-diagonal quasi-periodic disorder in momentum space,and characterize its localization and topological properties through dynamic observables.We then demonstrate the impact of interactions on the critically localized topological state,as a first experimental endeavor toward the clarification of many-body critical phase,the critical analogue of the many-body localized state.