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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.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Application of the regular associated solution model to the Cd-Te and Hg-Te binary systems

The regular associated solution model is used to treat the phase diagrams of the binary II-VI semiconductor alloy systems Hg-Te and Cd-Te. The equations for the species activity coefficients are used without approximations regarding the magnitudes of the various binary interchange energies or the functional dependence on component mol fraction. The values of the four-adjustable parameters required for description of each system are fixed by fitting liquidus data, and the resulting activity coefficients are used to calculate component partial pressures, which are compared with experimental values as an indpendent check of the validity of the model. The results show that the regular associated solution model provides a usefully accurate, but not complete, description for both the Hg-Te and Cd-Te systems. The relationship of this work to previous investigations is discussed.

Kelley, J. D.↗
DOE OSTI2021

Unusual dynamic susceptibility arising from soft ferromagnetic domains in MnBi 8 Te 13 and Sb-doped MnBi 2n Te 3n+1 (n = 2, 3)

MnBi$_{2n}$Te$_{3n+1}$ (MBT) is the first intrinsic magnetic topological insulator and is promising to host emergent phenomena such as quantum anomalous Hall effect. They can be made ferromagnetic by having n ≥ 4 or with Sb doping. In this work, we studied the magnetic dynamics in a few selected ferromagnetic (FM) MBT compounds, including MnBi 8 Te 13 and Sb doped MnBi$_{2n}$Te$_{3n+1}$ ($n = 2, 3)$ using AC susceptibility and magneto-optical imaging. Slow relaxation behavior is observed in all three compounds, suggesting its universality among FM MBT. We attribute the origin of the relaxation behavior to the irreversible domain movements since they only appear below the saturation fields when ferromagnetic domains form. The very soft ferromagnetic domain nature is revealed by the low-field fine-structured domains and high-field sea-urchin-shaped remanent-state domains imaged via our magneto-optical measurements. Finally, we ascribe the rare 'double-peak' behavior observed in the AC susceptibility under small DC bias fields to the very soft ferromagnetic domain formations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Pressure-Dependent Magnetic Properties of Quasi-2D Cr 2 Si 2 Te 6 and Mn 3 Si 2 Te 6

Recently, pressure has been used to induce structural and magnetic phase transitions in many layered quantum materials whose layers are linked by van der Waals forces. Materials with such weakly held layers allow for relatively easy manipulation of the superexchange mechanism, which can give rise to novel magnetic behavior. Here, using hydrostatic pressure as a disorderless means to manipulate the interlayer coupling, we applied pressure on two quasi-2D sister compounds, namely, Cr 2 Si 2 Te 6 (CST) and Mn 3 Si 2 Te 6 (MST), up to ~1 GPa. Magnetic property measurements with the application of pressure revealed that the ferromagnetic transition temperature decreases in CST, while the opposite occurs for the ferrimagnetic MST. In MST, magnetization decreases with the increase in pressure, and such a trend is not clearly observed within the pressure range studied for CST. The overall pressure effect on magnetic characteristics such as exchange couplings and magnetic anisotropy energies is also examined theoretically using density functional theory. Exchange coupling in MST is strongly frustrated, and the first nearest neighbor interaction is the most dominant of the components with the strongest pressure dependence. In CST, the exchange coupling parameters exhibit very little dependence on pressure. This combined experimental and theoretical work has the potential to expand to other relevant quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Reconstructing the Wave Function of Magnetic Topological Insulators MnBi 2 ⁢Te 4 and MnBi 4 ⁢Te 7 Using Spin-Resolved Photoemission

Despite their importance for exotic quantum effects, the surface electronic structure of magnetic topological insulators MnBi 2 ⁢Te 4 and MnBi 4 ⁢Te 7 remains poorly understood. Using high-efficiency spin- and angle-resolved photoemission spectroscopy, we directly image the spin-polarization and orbital character of the surface states in both compounds and map our observations onto a model wave function to describe the complex spin-orbital texture, which solidifies our understanding of the surface band structure by establishing the single-band nature of the most prominent states. Most importantly, our analysis reveals a new mechanism for reducing the magnetic gap of the topological surface states based on the orbital composition of the wave function.

Han, Xue [SLAC National Accelerator Laboratory (SL↗
DOE OSTI2022

Pressure-induced creation and annihilation of Weyl points in T d - Mo 0.5 W 0.5 Te 2 and 1 T " - Mo 0.5 W 0.5 Te 2

By means of first-principles density-functional theory calculations, we investigate the role of hydrostatic pressure in the electronic structure of the T d (Pmn2 1 ) and 1T" (Pm) phases of the Weyl semimetal Mo 0.5 W 0.5 Te 2 , which is a promising material for phase-change memory technology and superconductivity. We particularly focus on changes occurring in the distribution of the gapless Weyl points (WPs) within the 0 to 45 GPa pressure range. Here we further investigate the structural phase transition and lattice dynamics of the T d and 1T" phases within the aforementioned pressure range. Our calculations suggest that both the T d and 1T" phases of Mo 0.5 W 0.5 Te 2 host four WPs in their full Brillouin zone at zero pressure. The total number of WPs increases to 44 (36) with increasing pressure via pair creation up to 20 (15) GPa for the T d (1T") phase, and beyond this pressure pair annihilation of WPs starts occurring, leaving only 16 WPs at 45 GPa in both phases. The enthalpy versus pressure data reveal that the 1T" phase is more favorable below the critical pressure of 7.5 GPa; however, beyond this critical pressure the T d phase becomes enthalpically favorable. We also provide the calculated x-ray diffraction spectra along with the calculated Raman- and infrared-active phonon frequencies to facilitate the experimental identification of the studied phases

36 MATERIALS SCIENCE↗
DOE OSTI2023

A search for decays of the Higgs boson to invisible particles in events with a top-antitop quark pair or a vector boson in proton-proton collisions at $$\sqrt{s} = 13\,\text {Te}\hspace{-.08em}\text {V} $$

A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been performed using proton-proton collision data collected at $\sqrt{s} = 13$ TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138fb -1 . The 95% confidence level upper limit set on the branching fraction of the 125 GeV Higgs boson to invisible particles, B(H → inv), is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous B(H → inv) searches carried out at $\sqrt{s} = 7$, 8, and 13 TeV in complementary production modes. The combined upper limit at 95% confidence level on B(H → inv) is 0.15 (0.08 expected).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1985

An experimental TE sub 12 - TE sub 11 circular waveguide mode converter

Theoretical and experimental results for a prototype TE sub 12 to TE sub 11 circular waveguide mode converter are discussed. The system which requires such device, the high power Ka-Band transmitter is described briefly. A short review of coupled mode theory is given, and the theoretical performance of the final converter design is given. Experimental results for the fabricated converter are presented and compared with theory. A method of identifying the various circular waveguide modes in a multimode device is described. Given the close agreement between the theoretical predictions and experimental results, the computer code may be used with confidence in the design of future multimode tapers and mode converters.

Hoppe, D.↗
NASA NTRS1987

Directional couplers for detecting the TE sub 11 and TE sub 12 circular waveguide modes

The theoretical and experimental results for a pair of mode-selective directional couplers designed to detect the TE sub 11 and TE sub 12 modes in a multimode circular wavelength are described. A brief description of the design of the couplers is presented, followed by a comparison of their measured and calculated parameters. The couplers were used to measure the characteristics of a circular waveguide mode converter. The results of these measurements are described.

Hoppe, D.↗
DOE OSTI2022

Shot noise and differential conductance as signatures of putative topological superconductivity in FeSe 0.45 ⁢Te 0.55

We present a theory for the differential shot noise, dS/dV, as measured via shot-noise scanning tunneling spectroscopy, and the differential conductance, dI/dV, for tunneling into Majorana zero modes (MZMs) in the putative topological superconductor FeSe 0.45 Te 0.55 . We demonstrate that for tunneling into chiral Majorana edge modes near domain walls, as well as MZMs localized in vortex cores and at the end of defect lines, dS/dV vanishes whenever dI/dV reaches a quantized value proportional to the quantum of conductance. Furthermore, these results are independent of the particular orbital tunneling path, thus establishing a vanishing dS/dV concomitant with a quantized dI/dV, as universal signatures for Majorana modes in two-dimensional topological superconductors, irrespective of the material’s specific complex electronic band structure.

Iron-based superconductors↗
DOE OSTI2021

Constraints on Λ CDM extensions from the SPT-3G 2018 $EE$ and $TE$ power spectra

Here, we present constraints on extensions to the Λ CDM cosmological model from measurements of the E-mode polarization autopower spectrum and the temperature-E-mode cross-power spectrum of the cosmic microwave background (CMB) made using 2018 SPT-3G data. The extensions considered vary the primordial helium abundance, the effective number of relativistic degrees of freedom, the sum of neutrino masses, the relativistic energy density and mass of a sterile neutrino, and the mean spatial curvature. We do not find clear evidence for any of these extensions, from either the SPT-3G 2018 dataset alone or in combination with baryon acoustic oscillation and Planck data. None of these model extensions significantly relax the tension between Hubble-constant, H 0 , constraints from the CMB and from distance-ladder measurements using Cepheids and supernovae. The addition of the SPT-3G 2018 data to Planck reduces the square-root of the determinants of the parameter covariance matrices by factors of 1.3–2.0 across these models, signaling a substantial reduction in the allowed parameter volume. We also explore CMB-based constraints on H 0 from combined SPT, Planck, and ACT DR4 datasets. While individual experiments see some indications of different H 0 values between the TT, TE, and EE spectra, the combined H 0 constraints are consistent between the three spectra. For the full combined datasets, we report H 0 = 67.49 ± 0.53 km s -1 Mpc -1 , which is the tightest constraint on H0 from CMB power spectra to date and in 4.1σ tension with the most precise distance-ladder-based measurement of H 0 . The SPT-3G survey is planned to continue through at least 2023, with existing maps of combined 2019 and 2020 data already having ~ 3.5 x lower noise than the maps used in this analysis.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

A thermodynamic model of the Hg(0.8)Cd(0.2)Te-iodine transport system. I - Te-saturated source material. II - Source material composition within the homogeneity range

A thermochemical analysis of the Hg(0.8)Cd(0.2)Te-iodine vapor transport system is presented, and theoretical calculations of diffusion-controlled mass transport rates are made. The predicted mass fluxes are compared with experimental data obtained from transport experiments under vertical, stabilizing conditions reported earlier and with results of additional transport experiments conducted during the present study. Experimental mass transport rate studies of the transport system for fixed amount of excess Hg as a function of transport agent pressure are presented. The mass fluxes are determined for the vertical, stabilizing orientation of the density gradient relative to the gravitational vector. In order to compare experimental mass transport rates with computed values, the thermochemical analysis is extended to take the formation of Hg vacancies in the above compound into account along with their effect on the partial pressure of the system.

Chandra, D.↗
NASA NTRS1992

Electron mobility in n-type Hg(1-x)Cd(x)Te and Hg(1-x)Zn(x)Te alloys

Calculations of electron mobility in n-type mercury cadmium telluride (MCT), a candidate material for IR detectors, and n-type mercury zinc telluride (MZT) are compared. It is found that electron mobilities in MCT and MZT are nearly the same for equivalent energy gaps. The results are also found to compare will with experimental data. Directions of future research are briefly discussed.

Patterson, J. D.↗
DOE OSTI2021

Potential neutron-induced γ-ray background on natural tellurium relevant to 130 Te 0 ν ββ decay searches at the CUORE and SNO+ detectors

Gamma-ray production cross-section data have been obtained for the inelastic neutron scattering reactions 126,128,130 Te(n,n'γ) at five neutron energies between 3.6 and 10 MeV. We report data for the γ-ray energy region relevant to 0ν ββ decay of 130 Te with a Q ββ value of 2527.515 keV, assuming natural-abundance tellurium, as used at CUORE and SNO+. The natural abundance of 130 Te, 128 Te, and 126 Te is 34%, 32%, and 19%, respectively. For CUORE the γ-ray cascades from the excited state in 130 Te at 2527.06 keV and in 126 Te at 2533.85 keV are of concern. For SNO+, accounting for its inferior energy resolution, an additional four levels are important in 130 Te, an additional nine levels in 128 Te, and an additional eight levels in 126 Te. Of these, we report neutron-induced γ-ray production cross sections for the strongest transitions: the 2581.15 keV level in 130 Te, the 2494.20, 2508.06, and 2630.14 keV levels in 128 Te, and the 2496.83 and 2585.46 keV level in 126 Te. Here, the largest cross-section values were found for cascade γ-ray transitions to the ground state, while direct transitions to the ground state are very weak and were not observed in the present work. Both the CUORE and SNO+ detectors, however, may not be able to distinguish between cascade transitions and direct transitions to the ground state, making the neutron-induced excitation of the 2527.06 keV state of 130 Te in particular a potential problem for 0νββ decay searches of 130Te, because it matches its Q ββ value.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Materials Data on Te by Materials Project

Te is alpha Po structured and crystallizes in the orthorhombic Pmc2_1 space group. The structure is three-dimensional. there are two inequivalent Te sites. In the first Te site, Te is bonded to six Te atoms to form a mixture of corner and edge-sharing TeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are a spread of Te–Te bond distances ranging from 3.10–3.31 Å. In the second Te site, Te is bonded to six Te atoms to form a mixture of corner and edge-sharing TeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. Both Te–Te bond lengths are 3.20 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Te by Materials Project

Te is High Pressure (4-7GPa) Tellurium structured and crystallizes in the orthorhombic Pmc2_1 space group. The structure is three-dimensional. there are two inequivalent Te sites. In the first Te site, Te is bonded to six Te atoms to form a mixture of distorted edge and corner-sharing TeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Te–Te bond distances ranging from 3.06–3.46 Å. In the second Te site, Te is bonded to six Te atoms to form a mixture of distorted edge and corner-sharing TeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–5°. Both Te–Te bond lengths are 3.13 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Phonon modes and Raman signatures of MnBi 2n Te 3n+1 (n=1,2,3,4) magnetic topological heterostructures

An intrinsic antiferromagnetic topological insulator MnBi 2 Te 4 arises when intercalating a Mn-Te bilayer chain in a topological insulator, Bi 2 Te 3 . We present observations on the inter- and intralayer phonon modes of the generalized MnBi 2n Te 3n+1 (n=1,2,3,4) family using cryogenic low-frequency Raman spectroscopy with various polarization configurations. Two peaks at 66 and 112 cm –1 show abnormal perturbation in Raman linewidths below magnetic transition temperature due to spin-phonon coupling. In MnBi 4 Te 7 , B i2 Te 3 layers induce Davydov splitting of the A1g mode around 137 cm –1 at 5 K. The out-of-plane interlayer force constant estimated using the linear chain model was (3.98±0.14)×10 19 N/m 3 , three times weaker than that of Bi 2 Te 3 . Adding more Bi 2 Te 3 layers, such as MnBi 6 Te 10 and MnBi 8 Te 13 , makes Bi 2 Te 3 properties more dominant than magnetic properties. Our work experimentally and theoretically discovers the dynamics of phonon modes of MnBi 2n Te 3n+ 1 family, facilitating utilization of magnetic topological heterostructures.

74 ATOMIC AND MOLECULAR PHYSICS↗