Discovery of a hybrid topological quantum state in an elemental solid
arxiv(2024)
Abstract
Topology and interactions are foundational concepts in the modern
understanding of quantum matter. Their nexus yields three significant research
directions: competition between distinct interactions, as in the multiple
intertwined phases, interplay between interactions and topology that drives the
phenomena in twisted layered materials and topological magnets, and the
coalescence of multiple topological orders to generate distinct novel phases.
The first two examples have grown into major areas of research, while the last
example remains mostly untouched, mainly because of the lack of a material
platform for experimental studies. Here, using tunneling microscopy,
photoemission spectroscopy, and theoretical analysis, we unveil a "hybrid" and
yet novel topological phase of matter in the simple elemental solid arsenic.
Through a unique bulk-surface-edge correspondence, we uncover that arsenic
features a conjoined strong and higher-order topology, stabilizing a hybrid
topological phase. While momentum-space spectroscopy measurements show signs of
topological surface states, real-space microscopy measurements unravel a unique
geometry of topology-induced step edge conduction channels revealed on various
forms of natural nanostructures on the surface. Using theoretical models, we
show that the existence of gapless step edge states in arsenic relies on the
simultaneous presence of both a nontrivial strong Z2 invariant and a nontrivial
higher-order topological invariant, providing experimental evidence for hybrid
topology and its realization in a single crystal. Our discovery highlights
pathways to explore the interplay of different kinds of band topology and
harness the associated topological conduction channels in future engineered
quantum or nano-devices.
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