Phononic drumhead surface state in distorted kagome compound RhPb

TL;DR

This paper reports the experimental confirmation of a phononic drumhead surface state in distorted kagome RhPb, revealing unique phononic topological features such as flattened bands and Dirac points due to lattice distortion.

Contribution

It provides the first experimental evidence supporting the predicted lattice distortion and explores the resulting phononic topological surface states in RhPb.

Findings

Confirmation of kagome lattice distortion in RhPb

Observation of phononic drumhead surface state

Presence of Dirac nodal lines and triple degenerate Dirac points

Abstract

RhPb was initially recognized as one of a CoSn-like compounds with $P6/mmm$ symmetry, containing an ideal kagome lattice of $d$-block atoms. However, theoretical calculations predict the realization of the phonon soft mode which leads to the kagome lattice distortion and stabilization of the structure with $P\bar{6}2m$ symmetry [A. Ptok et al., Phys. Rev. B 104, 054305 (2021)]. Here, we present the single crystal x-ray diffraction results supporting this prediction. Furthermore, we discuss the main dynamical properties of RhPb with $P\bar{6}2m$ symmetry. The bulk phononic dispersion curves contain several flattened bands, Dirac nodal lines, and triple degenerate Dirac points. As a consequence, the phononic drumhead surface state is realized for the (100) surface, terminated by the zigzag-like edge of Pb honeycomb sublattice.