CaTe: a new topological node-line and Dirac semimetal

Abstract

Combining first-principles calculations and effective model analysis, we predict that CaTe is a topological node-line semimetal in the absence of the spin-orbit coupling. Using a slab model, we obtain the nearly flat drumhead surface state near the Fermi level. When the spin-orbit coupling is included, three node lines will evolve into a pair of Dirac points along the M−R line. These Dirac points are robust and protected by the C 4 rotation symmetry. Once this crystal symmetry is broken, the Dirac points will be eliminated, and the system becomes a strong topological insulator.npj Quantum Materials (2017) 2:3 ; doi:10.1038/s41535-016-0005-4 INTRODUCTIONTopological insulator (TI) has attracted broad interest in the past 10 years. [1][2][3][4][5][6][7] The unique property of TI is that it is an insulator in the bulk but has exotic metallic surface states due to the topological order. More recently, the research on topological states has been extended to three-dimensional (3D) semimetal systems. [8][9][10][11][12] These systems could demonstrate many fascinating phenomena, such as Weyl fermion quantum transport and various Hall effects, [13][14][15][16] consequently become the rising stars of the field. Up to now, three kinds of topological semimetals have been discovered, i.e., 3D Dirac semimetal (DSM), 12,[17][18][19][20][21] Weyl semimetal (WSM), 8,9,22,23 and node-line semimetal (NLS). [24][25][26][27][28][29] The 3D DSM has four-fold degeneracy point, which can be viewed as the kiss of two Weyl fermions with opposite chiralities in the Brillouin zone (BZ). Protected by the crystal symmetry and time reversal symmetry, 3D DSMs can be robust against external perturbations. Several materials have been theoretically predicted to be 3D DSMs 12,17-21 and some of them have already been confirmed by experiments. [30][31][32][33] If one breaks the time reversal symmetry 8,22,23,34 or the inversion symmetry, 35-38 the 3D DSM will evolve into WSM. Very recently, the predictions about WSM state in TaAs family 37,38 have been confirmed experimentally. [39][40][41][42] Unlike DSM and WSM whose band crossing points distribute at separate k points in the BZ, for a NLS the crossing points around the Fermi level form a closed loop. Several compounds have been proposed as NLSs, including Mackay-Terrones crystals, 25 Bernal graphite, 43 hyperhoneycomb lattices, 44 and antiperovskite Cu 3 PdN 26,27 and Cu 3 NZn. 27 In the absence of spin-orbit coupling (SOC), time reversal symmetry together with inversion or mirror symmetry will guarantee the occurrence of node line in 3D BZ for systems with band inversion. [25][26][27]37,45,46 Same with TI and WSM, NLS also has a characteristic surface state, namely, drumhead-like state. 24-29 Such a 2D flat band surface state may become a route to achieve high temperature superconductivity. 47,48 As a result, it is of great impetus to search new NLS.In this study, based on first-principles calculations and effective model analysis, we propose that CaTe in CsCl-type structure is a NLS with drumhea...

Symmetry demanded topological nodal-line materials

“…Including SOC typically turns the DNLS into either a DSM or a TI. Some predicted centrosymmetric DNL materials include cubic antiperovskite materials Cu 3 NX [83,84], CaTe [92], LaX [93], Ca 3 P 2 [94], CaP 3 family [95], BaSn 2 [96,97], AlB 2 -type diborides [98][99][100], and 3D carbon allotrope materials with negligible SOC such as Mackay-Terrones crystals [54] and hyperhoneycomb lattices [101]. In addition, two-dimensional DNL materials have also been proposed in monolayer Cu 2 Si [102] and honeycomb-kagome lattice [103].…”

“…CaTe [92]: CaTe is a CsCl-type structured alkaline-earth chalcogenide also in space group Pm3m No. 221.…”

Topological surface electronic states in candidate nodal-line semimetal CaAgAs

“…With strong spin-orbit coupling (SOC), the nodal lines in these materials are either protected by reflection or mirror symmetry, or gapped out due to the lack of such symmetries [18][19][20][21][22]. Recent examples/promising candidates of NLSM include Pb(Tl)TaSe 2 [23,24], ZrSiX (X = S, Se, Te) [25,26], CaP 3 [27], Ca 3 P 2 [28], BaSn 2 [29], Ag 2 S [30], CaTe [31], Cu 3 PdN [32], GdSbTe [33], body-centered orthorhombic C 16 [34], compressed black phosphorus [35], etc. However, the band structures of these materials are often so complex that multiple irrelevant trivial or nontrivial pockets coexist with the drumlike surface states at the Fermi level, masking the quantum transport signals from the nodal lines.…”

Antiferromagnetic topological nodal line semimetals

“…With certain symmetry breaking, NLSM will evolve into various exotic topological states such as TI and nodal point semimetals. The earlier studies on NLSM materials are focused in Θ-invariant systems without [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] and with [50][51][52][53] spin-orbit coupling (SOC).…”