I4/mcm-Si₄₈: An Ideal Topological Nodal-Line Semimetal

Abstract

Topological semimetals (TSMs) have attracted much attention due to their exotic physical properties and great application potential. Silicon-based TSMs are of particularly importance because of their abundance, nontoxicity, and natural compatibility with the current semiconductor industry. In this work, an ideal low-energy topological nodal-line semimetal (TNLSM) silicon (I4/mcm-Si 48 ) with a clean band crossing at the Fermi level is screened from thousands of silicon allotropes by general and transferable tight-binding and DFT calculations. The results of formation energy, phonon dispersion, ab initio molecular dynamics, and elastic constants show that I4/ mcm-Si 48 possesses good stability and is more stable than several synthesized silicon structures. Furthermore, I4/ mcm-Si 48 exhibits exotic photoelectric properties, and the Dirac fermions with high Fermi velocity (3.4−4.36 × 10 5 m/s) can be excited by low-energy photons. Our study provides a promising topological nodal-line semimetal for fundamental research and potential applications in semiconductor-compatible high-speed photoelectric devices.

Diamond-XII: a new type of exotic cubic carbon allotrope

“…In fact, Diamond-XII-1 and Diamond-XII-2 containing 12/1 and 60/2 total/inequivalent carbon atoms in their cubic cells are the previously proposed bcc-C6 35 and cl60 22 , respectively. Such small-size configurations can be quickly discovered by our recently developed RG 2 -code 19 ，which is a powerful code for generating crystal structures with well-defined geometrical feature [54][55][56][57][58][59] . The new Diamond-XII-3 with larger size can also be uncovered by RG 2 To show the relative stabilities of these Diamond-XII allotropes, we compare their average energies to those of some well-known cubic carbon phases, such as BC8 41 , BC12 6 , C3-205 38 , Cubane 40 , C22-sc 36 and cubic diamond (cd).…”

“…Such small-size configurations can be quickly discovered by our recently developed RG 2 -code 19 , which is a powerful code for generating crystal structures with well-defined geometrical features. [54][55][56][57][58][59] The new Diamond-XII-3 with a larger size can also be uncovered by RG 2 . It contains 168/84 carbon atoms in its cubic/primitive cell, in which only 4 of them are inequivalent.…”

High-Throughput Screening for Ideal 3D Carbon Topological Semimetals via Bottom-up Approach

“…From the definition of η in eq 1, the smaller the ideal index η, the higher the "quality" of the topological semimetal, which means that (i) it includes a large energy window in the characterization of ARPES in specific k paths that facilitates clearer identification and differentiation of energy bands; 73−76 (ii) it has high Fermi velocities near nodes that facilitate low-energy photon excitation of Dirac Fermions, suggesting potential applications in high-speed optoelectronics; 16,77 (iii) it holds small node energy fluctuations that indicate superior carrier behavior and significant topological Fermion properties; 78 and (iv) it possesses good energy stability that can improve the feasibility of experimental synthesis. 16 To gain a clearer understanding of the "ideal index" and the relationship between the different terms in eq 1, we further construct simplified two-band and four-band effective Hamiltonian models. First, the Hamiltonian for the two-band model can be written as a diagonal matrix: Considering that most of the topological semimetals are protected by mirror symmetry, we assume that the band crossings occur along the Γ → X(k x = 0.5, k y = k z = 0) and Γ → Z(k x = k y = 0, k z = 0.5) paths, which are protected by the mirror plane of k y = 0.…”

“…11−13 However, most of them contain toxic or heavy elements. Moreover, the materials with the ideal features (e.g., nodes located near the Fermi level, 14 clean linear bands with a large window, 15,16 high Fermi velocity, 17,18 and excellent energy stability) are extremely rare. In this context, the design or synthesis of new ideal topological semimetals is quite significant for next generation electronic devices with low-power and highspeed features.…”

General and transferable tight binding model for two-dimensional Bismuth allotropes

“…Therefore, it is of great importance to develop transferable TB model and parameters for efficient electronic properties calculations. In this work, we aim to propose a precise and transferable tight-binding method [32,33] based on the Bi sp 3 d 5 hybridization to calculate the electronic structures efficiently in a wide rangefor 2D Bi allotropes with different structural characteristics. The parameters were obtained by fitting the HSE band structures of three Bi allotropes (β-Bi, MBi and αω-Bi), and the results show that the SK parameters not only can reproduce the band structures of this three Bi allotropes but also can accurately calculate the electronic properties of other Bi allotropes, including the band structures, orbital projection and topological edge states.…”