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31 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on K2(NbSe2)3 by Materials Project

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.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electron-phonon coupling and spin fluctuations in the Ising superconductor NbSe2

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.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on Nb17Ir3Se40 by Materials Project

Nb7Ir3Se20(NbSe2)10 is trigonal omega-derived structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two Nb7Ir3Se20 sheets oriented in the (1, 0, -1) direction and two NbSe2 sheets oriented in the (1, 0, -1) direction. In each Nb7Ir3Se20 sheet, there are four inequivalent Nb+4.12+ sites. In the first Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form distorted NbSe6 octahedra that share edges with two equivalent IrSe6 octahedra and edges with four NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.52–2.73 Å. In the second Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form edge-sharing NbSe6 octahedra. There are four shorter (2.67 Å) and two longer (2.71 Å) Nb–Se bond lengths. In the third Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form NbSe6 octahedra that share edges with two equivalent IrSe6 octahedra and edges with four NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.49–2.81 Å. In the fourth Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form NbSe6 octahedra that share edges with two equivalent IrSe6 octahedra and edges with four NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.50–2.76 Å. There are two inequivalent Ir+3.33+ sites. In the first Ir+3.33+ site, Ir+3.33+ is bonded to six Se2- atoms to form IrSe6 octahedra that share edges with two equivalent IrSe6 octahedra and edges with four NbSe6 octahedra. There are a spread of Ir–Se bond distances ranging from 2.52–2.58 Å. In the second Ir+3.33+ site, Ir+3.33+ is bonded to six Se2- atoms to form IrSe6 octahedra that share edges with two equivalent IrSe6 octahedra and edges with four equivalent NbSe6 octahedra. There are four shorter (2.57 Å) and two longer (2.61 Å) Ir–Se bond lengths. There are ten inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to one Nb+4.12+ and two equivalent Ir+3.33+ atoms. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to one Nb+4.12+ and two equivalent Ir+3.33+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the fifth Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.12+ and one Ir+3.33+ atom. In the sixth Se2- site, Se2- is bonded in a 3-coordinate geometry to one Nb+4.12+ and two equivalent Ir+3.33+ atoms. In the seventh Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the eighth Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.12+ and one Ir+3.33+ atom. In the ninth Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.12+ and one Ir+3.33+ atom. In the tenth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In each NbSe2 sheet, there are five inequivalent Nb+4.12+ sites. In the first Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form edge-sharing NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.59–2.73 Å. In the second Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form edge-sharing NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.54–2.73 Å. In the third Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form edge-sharing NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.54–2.75 Å. In the fourth Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form edge-sharing NbSe6 octahedra. There are four shorter (2.65 Å) and two longer (2.66 Å) Nb–Se bond lengths. In the fifth Nb+4.12+ site, Nb+4.12+ is bonded to six Se2- atoms to form edge-sharing NbSe6 octahedra. There are a spread of Nb–Se bond distances ranging from 2.56–2.72 Å. There are ten inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+4.12+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the fifth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the sixth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the seventh Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the eighth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent Nb+4.12+ atoms. In the ninth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms. In the tenth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb+4.12+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3MoSe8 by Materials Project

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.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbHSe2 by Materials Project

(NbSe2)2H2 is H-Phase structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two hydrogen molecules and two NbSe2 sheets oriented in the (0, 0, 1) direction. In each NbSe2 sheet, Nb3+ 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 Nb3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3WSe8 by Materials Project

NbWSe4(NbSe2)2 is Molybdenite-derived structured and crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of two NbSe2 sheets oriented in the (1, 0, 0) direction and two NbWSe4 sheets oriented in the (1, 0, 0) direction. In each NbSe2 sheet, Nb+4.67+ 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 2.61–2.63 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+4.67+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+4.67+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+4.67+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Nb+4.67+ atoms. In each NbWSe4 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 WSe6 pentagonal pyramids. There are four shorter (2.61 Å) and two longer (2.64 Å) Nb–Se bond lengths. W2+ is bonded to six Se2- atoms to form distorted WSe6 pentagonal pyramids that share edges with two equivalent WSe6 pentagonal pyramids and edges with four equivalent NbSe6 pentagonal pyramids. There are two shorter (2.56 Å) and four longer (2.59 Å) W–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.67+ and one W2+ atom. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to one Nb+4.67+ and two equivalent W2+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to one Nb+4.67+ and two equivalent W2+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Nb+4.67+ and one W2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbMoSe4 by Materials Project

NbSe2MoSe2 is Molybdenite-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of one MoSe2 sheet oriented in the (0, 0, 1) direction and one NbSe2 sheet oriented in the (0, 0, 1) direction. In the MoSe2 sheet, Mo3+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.56 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo3+ atoms. 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.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbWSe4 by Materials Project

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.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ultralow-temperature cryogenic transmission electron microscopy using a new helium flow cryostat stage

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.

Charge density wave↗
DOE OSTI2021

Simplified feedback control system for scanning tunneling microscopy

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).

Martín-Vega, Francisco (ORCID:0000000333177833)↗
DOE OSTI2026

Microscopic Scattering Approach to In-Gap States

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

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Optically induced quantum transitions in direct probed mesoscopic NbSe 2 for prototypical bolometers

Superconducting transition-edge sensors (TES) have emerged as fascinating devices to detect broadband electromagnetic radiation with low thermal noise. The advent of metallic transition metal dichalcogenides, such as NbSe 2 , has also created an impetus to understand their low-temperature properties, including superconductivity. Interestingly, NbSe 2 -based sensor within the TES framework remains unexplored. In this work, direct-probed superconducting NbSe 2 absorbers led to a proof-of-concept demonstration for the transduction of incoming light to heat, where a thermodynamic superconducting phase transition in NbSe 2 was evident to switch it to the normal-state, when biased below its superconducting transition temperature. A wavelength-dependent response of its optical absorption properties was observed, based on the incident optical excitation source used. Furthermore, extensive optical characterization studies were conducted using Raman spectroscopy, where the in-plane and out-of-plane thermal conductivity was empirically determined. Our results open new possibilities for the use of NbSe 2 in superconducting radiation detectors, including in a TES framework

47 OTHER INSTRUMENTATION↗