Pseudo Dirac nodal sphere semimetal

Abstract

Topological semimetals (TSMs) in which conduction and valence bands cross at zero-dimensional (0D) Dirac nodal points (DNPs) or 1D Dirac nodal lines (DNLs), in 3D momentum space, have recently drawn much attention due to their exotic electronic properties. Here we generalize the TSM state further to a higher-dimensional Dirac nodal sphere (DNS) or pseudo DNS (PDNS) state, with the band crossings forming a 2D closed or approximate sphere at the Fermi level. This new TSM state can exhibit unique electronic properties, making DNS/PDNS a new type of fermion beyond DNP/DNL paradigm. In the realistic crystals, we demonstrate two possible types of PDNS states underlied by different crystalline symmetries, which are characterized with a spherical backbone consisting of multiple DNLs and approximate band degeneracy in between the DNLs. We identify all the possible band crossings with pairs of 1D irreducible representations to form the PDNS states in 32 point groups. Importantly, we discover that strained M H3 (M = Y, Ho, Tb, Nd) and Si3N2 are materials candidates to realize these two types of PDNS states, respectively. As a high-symmetryrequired state, the PDNS semimetal can be regarded as the "parent phase" for other topological gapped and gapless states.

Effect of Mechanical Strain on the Optical Properties of Nodal‐Line Semimetal ZrSiS

“…In comparison to conventional metals, Dirac semimetals have raised intense interest both from fundamental and applied perspectives due to their intriguing optical properties . Recently, optical spectra of ZrSiS were measured in a large frequency range, from the near‐infrared to the visible .…”

Fermi-level Dirac crossings in 4d and 5d cubic metal oxides: NaPd3O4Teicher1, Lamontagne2, Schoop3 et al. 2019Phys. Rev. B80110View full textAdd to dashboardCite

“…We have shown that the high symmetry structures of NaM The P m3n cubic space group appears promising for the generation of a stable nodal cube state with surface states that could host exciting correlated electron physics. 11 While the compounds discussed here have significant SOC that prevents the realization of a true nodal cube, this state might be achieved in related systems by lowering SOC using lighter elements. The presence of a full nodal cube in the Pt compound without SOC also gives us some hints as to how we might go about creating such a state in a real material.…”

“…The compounds (Ca/Sr)M 3 O 4 have previously been suggested to be topological semimetals, but these compounds are actually insulating both at appropriate levels of electronic structure theory as well as in experimental studies. 18,32 We present here a detailed electronic structure description of the two compounds NaPd 3 O 4 and NaPt 3 O 4 using a combination of plane-wave pseudopotential and planewave local orbital density functional theory calculations in tandem with tight-binding models to identify Dirac crossings near the Fermi level that appear to form a nodal cube, not unlike the nodal-sphere semimetallic state proposed previously by Wang et al 11 Spin-orbit coupling fragments this nodal cubic state into 14 protected Dirac crossings in both the Pd and Pt compounds. This work points to the potential of complex oxides to enrich the domain of Dirac and related quantum materials and supports the view that there may be a role for previously ignored features in the electronic structure playing a role in the catalytic properties of compounds of the platinum group metals.…”

“…10 Nodal-line semimetals with certain symmetry protections exhibit drumhead-shaped surface states that are proposed to host novel correlated electron physics. 9 Recently, it has been proposed that rather than displaying nodal lines, there could exist compounds in which the degenerate band crossings trace a connected 3D surface -a spherical shell -in the Brillouin zone, 11 these nodal-sphere semimetals could exhibit similar correlated surface states.…”

Prediction of crossing nodal-lines and large intrinsic spin Hall conductivity in topological Dirac semimetal Ta3As family

“…It is known that the nodal line can be protected by appropriate symmetries, such as mirror symmetry, time-reversal symmetry, and inversion symmetry [24][25][26] . Interestingly, the nodal line states have been classified into various types, e.g., isolated closed nodal ring, nodal chain, nodal link, nodal knots, nodal straight line, and even crossing nodal-line (CNL) 27,28 . Until now, the real NLSMs that can host CNL are very rare 28 .…”