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NbSe2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one NbSe2 sheet oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form edge-sharing NbSe6 octahedra. All Nb–Se bond lengths are 2.62 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.63 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the orthorhombic C222_1 space group. The structure is two-dimensional and consists of four NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are three shorter (2.63 Å) and three longer (2.64 Å) Nb–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of four NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.63 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of four NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.62 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of four NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.63 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the orthorhombic Fmm2 space group. The structure is two-dimensional and consists of two NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.62 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.63 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
Na(NbSe2)2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one Na(NbSe2)2 sheet oriented in the (0, 0, 1) direction. Na1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are three shorter (2.96 Å) and three longer (2.97 Å) Na–Se bond lengths. There are two inequivalent Nb+3.50+ sites. In the first Nb+3.50+ site, Nb+3.50+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are three shorter (2.62 Å) and three longer (2.65 Å) Nb–Se bond lengths. In the second Nb+3.50+ site, Nb+3.50+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are three shorter (2.62 Å) and three longer (2.65 Å) Nb–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent Nb+3.50+ atoms to form a mixture of distorted edge, face, and corner-sharing SeNa3Nb3 octahedra. In the second Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent Nb+3.50+ atoms to form a mixture of distorted edge, face, and corner-sharing SeNa3Nb3 pentagonal pyramids. The corner-sharing octahedral tilt angles are 40°. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+3.50+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+3.50+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the orthorhombic Amm2 space group. The structure is two-dimensional and consists of four NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.63 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two NbSe2 sheets oriented in the (0, 0, 1) direction. Nb4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.63 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb4+ atoms.
NbSe2 is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of four niobium selenide molecules. Nb4+ is bonded in a linear geometry to two equivalent Se2- atoms. Both Nb–Se bond lengths are 2.41 Å. Se2- is bonded in a single-bond geometry to one Nb4+ atom.
Ti(NbSe2)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ti4+ is bonded to six Se2- atoms to form TiSe6 octahedra that share corners with twelve equivalent NbSe6 octahedra, edges with two equivalent TiSe6 octahedra, and faces with two equivalent NbSe6 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are two shorter (2.58 Å) and four longer (2.65 Å) Ti–Se bond lengths. Nb2+ is bonded to six Se2- atoms to form distorted NbSe6 octahedra that share corners with six equivalent TiSe6 octahedra, edges with six equivalent NbSe6 octahedra, and a faceface with one TiSe6 octahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are a spread of Nb–Se bond distances ranging from 2.59–2.87 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent Ti4+ and three equivalent Nb2+ atoms. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to one Ti4+ and three equivalent Nb2+ atoms.
Mn(NbSe2)4 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Nb+3.50+ sites. In the first Nb+3.50+ site, Nb+3.50+ is bonded to six equivalent Se2- atoms to form distorted NbSe6 pentagonal pyramids that share edges with six equivalent NbSe6 pentagonal pyramids and faces with two equivalent MnSe6 octahedra. All Nb–Se bond lengths are 2.64 Å. In the second Nb+3.50+ site, Nb+3.50+ is bonded to six Se2- atoms to form distorted NbSe6 pentagonal pyramids that share corners with four equivalent MnSe6 octahedra and edges with six NbSe6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 49°. There are two shorter (2.59 Å) and four longer (2.64 Å) Nb–Se bond lengths. Mn2+ is bonded to six equivalent Se2- atoms to form MnSe6 octahedra that share corners with twelve equivalent NbSe6 pentagonal pyramids and faces with two equivalent NbSe6 pentagonal pyramids. All Mn–Se bond lengths are 2.60 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+3.50+ atoms. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to three Nb+3.50+ and one Mn2+ atom.
K2(NbSe2)3 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 6-coordinate geometry to six Se2- atoms. All K–Se bond lengths are 3.27 Å. In the second K1+ site, K1+ is bonded in a 6-coordinate geometry to six Se2- atoms. All K–Se bond lengths are 3.27 Å. There are two inequivalent Nb+3.33+ sites. In the first Nb+3.33+ site, Nb+3.33+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are two shorter (2.63 Å) and four longer (2.64 Å) Nb–Se bond lengths. In the second Nb+3.33+ site, Nb+3.33+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are a spread of Nb–Se bond distances ranging from 2.62–2.64 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent K1+ and three Nb+3.33+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent K1+ and three Nb+3.33+ atoms. In the third Se2- site, Se2- is bonded to two equivalent K1+ and three Nb+3.33+ atoms to form a mixture of distorted edge and corner-sharing SeK2Nb3 square pyramids. In the fourth Se2- site, Se2- is bonded to two equivalent K1+ and three Nb+3.33+ atoms to form a mixture of distorted edge and corner-sharing SeK2Nb3 square pyramids.
Abstract Ising superconductivity, observed in NbSe 2 and similar materials, has generated tremendous interest. Recently, attention was called to the possible role that spin fluctuations (SF) play in this phenomenon, in addition to the dominant electron–phonon coupling (EPC); the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet Leggett oscillations. However, these hypotheses have not been put to a quantitative test. In this paper, we report first principle calculations of the EPC and also estimate coupling with SF, including full momentum dependence. We find that: (1) EPC is strongly anisotropic, largely coming from the $$K-{K}^{{\prime} }$$ K − K ′ scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by SF, but anisotropy remains as above; and, (3) we do find the possibility of a Leggett mode, not in a singlet–triplet but in an s ++ – s ± channel.
NbMoSe4(NbSe2)2 is Molybdenite-derived structured and crystallizes in the monoclinic Pm space group. The structure is two-dimensional and consists of one NbMoSe4 sheet oriented in the (0, 0, 1) direction and one NbSe2 sheet oriented in the (0, 0, 1) direction. In the NbMoSe4 sheet, Nb+4.67+ is bonded to six Se2- atoms to form distorted NbSe6 pentagonal pyramids that share edges with two equivalent NbSe6 pentagonal pyramids and edges with four equivalent MoSe6 pentagonal pyramids. There are four shorter (2.61 Å) and two longer (2.63 Å) Nb–Se bond lengths. Mo2+ is bonded to six Se2- atoms to form distorted MoSe6 pentagonal pyramids that share edges with two equivalent MoSe6 pentagonal pyramids and edges with four equivalent NbSe6 pentagonal pyramids. There are two shorter (2.57 Å) and four longer (2.58 Å) Mo–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to one Nb+4.67+ and two equivalent Mo2+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.67+ and one Mo2+ atom. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.67+ and one Mo2+ atom. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to one Nb+4.67+ and two equivalent Mo2+ atoms. In the NbSe2 sheet, there are two inequivalent Nb+4.67+ sites. In the first Nb+4.67+ site, Nb+4.67+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are four shorter (2.62 Å) and two longer (2.63 Å) Nb–Se bond lengths. In the second Nb+4.67+ site, Nb+4.67+ is bonded to six Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. There are four shorter (2.62 Å) and two longer (2.63 Å) Nb–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.67+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.67+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.67+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.67+ atoms.