Observation of the dual quantum spin Hall insulator by density-tuned correlations in a van der Waals monolayer
arxiv(2024)
摘要
The convergence of topology and correlations represents a highly coveted
realm in the pursuit of novel quantum states of matter. Introducing electron
correlations to a quantum spin Hall (QSH) insulator can lead to the emergence
of a fractional topological insulator and other exotic time-reversal-symmetric
topological order, not possible in quantum Hall and Chern insulator systems.
However, the QSH insulator with quantized edge conductance remains rare, let
alone that with significant correlations. In this work, we report a novel dual
QSH insulator within the intrinsic monolayer crystal of TaIrTe4, arising from
the interplay of its single-particle topology and density-tuned electron
correlations. At charge neutrality, monolayer TaIrTe4 demonstrates the QSH
insulator that aligns with single-particle band structure calculations,
manifesting enhanced nonlocal transport and quantized helical edge conductance.
Interestingly, upon introducing electrons from charge neutrality, TaIrTe4 only
shows metallic behavior in a small range of charge densities but quickly goes
into a new insulating state, entirely unexpected based on TaIrTe4's
single-particle band structure. This insulating state could arise from a strong
electronic instability near the van Hove singularities (VHS), likely leading to
a charge density wave (CDW). Remarkably, within this correlated insulating gap,
we observe a resurgence of the QSH state, marked by the revival of nonlocal
transport and quantized helical edge conduction. Our observation of helical
edge conduction in a CDW gap could bridge spin physics and charge orders. The
discovery of a dual QSH insulator introduces a new method for creating
topological flat minibands via CDW superlattices, which offer a promising
platform for exploring time-reversal-symmetric fractional phases and
electromagnetism.
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