Dynamical Properties of T3Pb2Ch2 (T=Pd,Pt and Ch=S,Se) with Transition Metal Kagome Net

Abstract

AbstractShandite with Ni3Pb2S2 chemical formula and Rm symmetry contains the kagome sublattice formed by transition metal atoms. Recent experimental results confirmed the possibility of successfully synthesizing Pd3Pb2Ch2 (Ch=S,Se) with the same structure. This paper theoretically investigates the dynamical properties of such compounds. Furthermore, we study the possibility of realizing Pt3Pb2Ch2 with the shandite structure. This study shows that the Pd3Pb2Ch2 and Pt3Pb2S2 are stable with Rm symmetry. In the case of Pt3Pb2S2, there is a soft mode, which is the source of the structural phase transition from Rm to Rc symmetry, related to the distortion within the kagome sublattice. This study discusses realized phonon nodal lines in bulk phonon dispersions in upper frequency modes. It shows that the shandite structure can host phonon surface states, with a strong dependence on the type of surface. Additionally, chiral phonons with circular motion of the Pb atoms around the equilibrium position are realized.