Unconventional excitations and orbital-driven low-energy dispersions in chiral topological semimetals PdAsS, PdSbSe, and PdBiTe: a first-principles study

TL;DR

This study uses first-principles calculations to explore unconventional excitations and Weyl points in chiral topological semimetals PdAsS, PdSbSe, and PdBiTe, revealing new topological features and surface states.

Contribution

It reports the discovery of multiple higher fold excitations, new type-II Weyl points, and detailed low-energy dispersion characteristics in three chiral semimetals using DFT with and without SOC.

Findings

Identified four types of unconventional excitations at high symmetry points.

Discovered 8 new type-II Weyl points without SOC and 12 with SOC.

Analyzed surface states and Fermi arcs related to these excitations.

Abstract

The theoretical dispersion of higher fold excitations are typically governed by space group symmetry. However, physical factors affecting local structural and electronic environment such as atomic arrangement, orbital overlaps, etc., largely alter the behavior of quasiparticle around higher fold nodes. In this work, we consider three chiral material candidates (space group P$2_13$) which exhibit systematic variations in physical parameters by virtue of their constituent elements. We perform a detailed and systematic study of these materials using DFT in absence and presence of spin-orbit coupling (SOC). Four different kinds of unconventional excitations were observed in all three materials at $\Gamma$- and R-point in the full BZ. In absence of SOC, we find spin-1 ($\Gamma$) and double Weyl (R) excitations, where a Rarita-Schwinger-Weyl fermion ($\Gamma$) and double spin-1 excitation (R) are found in presence of SOC. All of these higher fold nodes lie in energy range of $\left(-0.5,-0.85\right)$eV. Remarkably, we also find total of eight new type-II Weyl points even in absence SOC on $\Gamma$-R line in these materials. In presence of SOC, 12 new Weyl nodes of type-II nature at general momenta ($k_x,k_y,k_z$)$\frac{2\pi}{a}$ are also observed. The presence of these Weyl nodes have not been reported in any of the earlier works. Further, analyzing the low-energy dispersion of spin-1 excitations in these materials we find that otherwise flat middle band in PdBiTe is almost parabolic due strong hybridization. On the other hand, relatively flat middle bands can be observed in PdAsS and PdSbSe in low-energy scale. In case of double spin-1 excitations, surprisingly, we see linearly dispersing middle bands in PdSbSe whereas middle bands in PdAsS and PdSbSe are parabolic even in low-energy scale. Lastly, we present non-trivial surface states and Fermi arcs associated with higher fold excitations.