Fermi-level Dirac crossings in 4d and 5d cubic metal oxides: NaPd3O4

Abstract

The cubic oxide metals NaM3O4 (M = Pd or Pt) crystallize in the non-symmorphic P m3n space group. First-principles calculations are employed here to understand the role of the MO4 square planes and M-M interactions in the development of the electronic structure. The compounds host numerous Dirac crossings near the Fermi level which, in the absence of spin-orbit coupling, appear to form a cubic nodal state. Spin-orbit coupling fragments this nodal state into smaller regions with Dirac-like character, with the fragmenting being more pronounced in the the M = Pt compound.

Weyl nodes and magnetostructural instability in antiperovskite Mn3ZnC

“…In general, although individual band crossings and nodal lines can be protected, there are no symmetries that can fully protect a 3D nodal surface in the presence of SOC. 52,53 The nodal surfaces depicted in Fig. 3(d,e) about R are no exception.…”

Bonding and Electronic Nature of the Anionic Framework in LaPd3S4

“…The known compounds are not evenly distributed between X = O and X = S. Instead, it appears that when X = O, cations transferring up to two electrons per Pd 3 O 4 unit are stable (including the 0-electron "cation vacancy" Pd 3 O 4 binary, implying stable average Pd valences of 2.66+ to 2+. 21 On the other hand, when X = S, cations must transfer more than two electrons per Pd 3 S 4 unit for a stable structure to result, i.e., average Pd valences <2+, Table 5. Does this trend reflect an underlying principle of bonding, or is it simply the consequence of a bias in the set of known materials?…”

“…The emergence of exotic electronic properties in extended solids is governed by the chemical bonding and symmetries that are present. Understanding how local chemical motifs give rise to interesting features in band structures is essential to the design of theoretically predicted, and often quantum, states of matter. − Elucidating how the atomic arrangement and electron count stabilize structures is essential in experimentally realizing such materials. Symmetry has long been a key tool to classify the mapping between local chemistry and band structure.…”

“…Recently, the field of topology has added to these additional considerations to enable a full understanding of the resultant electronic behavior of a material. Aided by the computational accuracy in predicting the topological features such as the double-struckZ 2 indices and in confirming key features in band structures such as linear dispersions in Dirac materials or band inversions in topological insulators, recent work has established a voluminous set of chemical principles to design new families of topological materials. ,− , …”

“…Recent computational work has identified the palladium bronzes NaPd 3 O 4 and LaPd 3 S 4 as hosting such eight-fold fermion states. , Both crystallize in cubic symmetry space group Pm -3 n that has the required symmetries to host these highly degenerate states at the R = (1/2, 1/2, 1/2) point of the Brillouin zone. , The structure consists of corner-sharing PdX 4 (X = O, S) units that form three orthogonal but symmetry-related 1D chains of stacked [PdX 4 ] units that together form an anionic framework that accepts charge from the Na + /La 3+ cation. Both are known to be metallic, in agreement with computational predictions (and in contrast to other 8-fold fermion candidates such as Bi 2 CuO 4 ). , A recent theoretical study elucidated in detail how topological states arise from the local chemical bonding in NaPd 3 O 4 . Yet the existing literature is sparse on the crystal growth and low-temperature physical properties .…”