Discovery of a Topological Charge Density Wave
arxiv(2024)
摘要
Charge density waves (CDWs) appear in numerous condensed matter platforms,
ranging from high-Tc superconductors to quantum Hall systems. Despite such
ubiquity, there has been a lack of direct experimental study on boundary states
that can uniquely stem from the charge order. Here, using scanning tunneling
microscopy, we directly visualize the bulk and boundary phenomenology of CDW in
a topological material, Ta2Se8I. Below the transition temperature (TCDW = 260
K), tunneling spectra on an atomically resolved lattice reveal a large
insulating gap in the bulk and on the surface, exceeding 500 meV, surpassing
predictions from standard weakly-coupled mean-field theory. Spectroscopic
imaging confirms the presence of CDW, with LDOS maxima at the conduction band
corresponding to the LDOS minima at the valence band, thus revealing a π
phase difference in the respective CDW order. Concomitantly, at a monolayer
step edge, we detect an in-gap boundary mode with modulations along the edge
that match the CDW wavevector along the edge. Intriguingly, the phase of the
edge state modulation shifts by π within the charge order gap, connecting
the fully gapped bulk (and surface) conduction and valence bands via a smooth
energy-phase relation. This bears similarity to the topological spectral flow
of edge modes, where the boundary modes bridge the gapped bulk modes in energy
and momentum magnitude but in Ta2Se8I, the connectivity distinctly occurs in
energy and momentum phase. Notably, our temperature-dependent measurements
indicate a vanishing of the insulating gap and the in-gap edge state above
TCDW, suggesting their direct relation to CDW. The theoretical analysis also
indicates that the observed boundary mode is topological and linked to CDW.
更多查看译文
AI 理解论文
溯源树
样例
![](https://originalfileserver.aminer.cn/sys/aminer/pubs/mrt_preview.jpeg)
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要