SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
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 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 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.
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.
NbSe2WSe2 is Molybdenite-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of one NbSe2 sheet oriented in the (0, 0, 1) direction and one WSe2 sheet oriented in the (0, 0, 1) direction. In the NbSe2 sheet, Nb5+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing NbSe6 pentagonal pyramids. All Nb–Se bond lengths are 2.61 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Nb5+ atoms. In the WSe2 sheet, W3+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing WSe6 pentagonal pyramids. All W–Se bond lengths are 2.57 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent W3+ atoms.
Advances in cryogenic electron microscopy have opened new avenues for probing quantum phenomena in correlated materials. This study reports the installation and performance of a new side-entry condenZero cryogenic cooling system for JEOL (Scanning) Transmission Electron Microscopes (S/TEM), utilizing compressed liquid helium (LHe) and designed for imaging and spectroscopy at ultra-low temperatures. The system includes an external dewar mounted on a vibration-damping stage and a pressurized, low-noise helium transfer line with a remotely controllable needle valve, ensuring stable and efficient LHe flow with minimal thermal and mechanical noise. Performance evaluation demonstrates a stable base temperature of 4.37 K measured using a Cernox bare chip sensor on the holder with temperature fluctuations within ±0.004 K. Complementary in-situ electron energy-loss spectroscopy (EELS) via aluminum bulk plasmon analysis was used to measure the local specimen temperature and validate cryogenic operation during experiments. The integration of cryogenic cooling with other microscopy techniques, including electron diffraction and Lorentz TEM, was demonstrated by resolving charge density wave (CDW) transitions in NbSe2 using electron diffraction, and imaging nanometric magnetic skyrmions in MnSi via Lorentz TEM. In conclusion, this platform provides reliable cryogenic operation below 7 K, establishing a low-drift route for direct visualization of electronic and magnetic phase transformations in quantum materials.
A Scanning Tunneling Microscope (STM) is one of the most important scanning probe tools available to study and manipulate matter at the nanoscale. In a STM, a tip is scanned on top of a surface with a separation of a few Å. Often, the tunneling current between the tip and the sample is maintained constant by modifying the distance between the tip apex and the surface through a feedback mechanism acting on a piezoelectric transducer. This produces very detailed images of the electronic properties of the surface. The feedback mechanism is nearly always made using a digital processing circuit separate from the user computer. Here, we discuss another approach using a computer and data acquisition through the universal serial bus port. We find that it allows successful ultralow noise studies of surfaces at cryogenic temperatures. We show results on different compounds including a type II Weyl semimetal (WTe2), a quasi-two-dimensional dichalcogenide superconductor (2H–NbSe2), a magnetic Weyl semimetal (Co3Sn2S2), and an iron pnictide superconductor (FeSe).
We develop a microscopic scattering formalism to describe Yu-Shiba-Rusinov (YSR) states due to a single Cr adatom on the Bi-terminated surface of beta Bi2Pd, by combining ab initio Wannier functions with a real-space Green's function approach in the Bogoliubov-de Gennes formalism[1]. Our framework reproduces key scanning tunneling spectroscopy features, including a single particle-hole asymmetric YSR peak and isotropic dIdV maps around the impurity. Decomposing the YSR states reveals contributions from four nearly degenerate C4v representations, with energy broadening masking their individual signatures. Spin-orbit coupling induces partial spin polarization, while the spatial asymmetry between particle and hole components arises from Cr d-Bi p hybridization. These results highlight the importance of realistic band structures and microscopic modeling for interpreting STM data for magnetic in-gap states on superconductors. Further advances examining layered 2D material surfaces, such as NbSe2, will be described[2]. For this system the superconducting properties are obtained from a full anisotropic Eliashberg calculation of the superconducting order parameter along with the charge density wave gap. Additional features associated with proposals to measure the dynamics of these individual YSR states will be presented. [1] arXiv:2507.08740 [2] arXiv:2507.11856