Phononic Stiefel-Whitney topology with corner vibrational modes in two-dimensional Xenes and ligand-functionalized derivatives

Abstract

Two-dimensional (2D) Stiefel-Whitney (SW) insulator is a fragile topological state characterized by the second SW class in the presence of space-time inversion symmetry. So far, SWIs have been proposed in several electronic materials but seldom in phononic systems. Here we recognize that a large class of 2D buckled honeycomb crystals termed Xenes and their ligand-functionalized derivatives realize the nontrivial phononic SW topology. The phononic SWIs are identified by a nonzero second SW number $w_2=1$, associated with gaped edge states and robust topological corner modes. Despite the versatility of electronic topological properties in these materials, the nontrivial phononic SW topology is mainly attributed to the double band inversion between in-plane acoustic and out-of-plane optical bands with opposite parities due to the structural buckling of the honeycomb lattice. Our findings not only reveal an overlooked phononic topological property of 2D Xene-related materials, but also afford abundant readily synthesizable material candidates with simple phononic spectra for further experimental studies of phononic SW topology physics.

Phys. Rev. B (in press)

References in corpus (18)

• Topological Insulators with Inversion Symmetry
• Control of graphene's properties by reversible hydrogenation
• Germanene: a novel two-dimensional Germanium allotrope akin to Graphene and Silicene
• $(d-2)$-dimensional edge states of rotation symmetry protected topological states
• Valley-Polarized Metals and Quantum Anomalous Hall Effect in Silicene
• Reflection symmetric second-order topological insulators and superconductors
• Higher-order topological insulators and semimetals on the breathing Kagome and pyrochlore lattices
• Prediction of Near-Room-Temperature Quantum Anomalous Hall Effect on Honeycomb Materials
• Liganded Xene as a Prototype of Two-Dimensional Stiefel-Whitney Insulators
• $PT$ Symmetric Real Dirac Fermions and Semimetals
• First Principles Calculations for Topological Quantum Materials
• Boundary criticality of $PT$-invariant topology and second-order nodal-line semimetals
• Second Order Topological Insulator State in Hexagonal Lattices and its Abundant Material Candidates
• Kekule Lattice in Graphdiyne: Coexistence of Phononic and Electronic Higher-Order Band Topology
• Phononic real Chern insulator with protected corner modes in graphynes
• Buckled honeycomb group-$V$--$S_6$ symmetric $(d-2)$ higher order topological insulators
• Second-order and real Chern topological insulator in twisted bilayer $\alpha$-graphyne
• Topological edge and corner states and fractional corner charges in blue phosphorene

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