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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Solvent Effect on the Photoinduced Structural Change of a Phosphorescent Molecular Butterfly

Abstract Photoinduced structural changes (PSC) is one of the fundamental excited‐state dynamic processes, and yet often very challenging to distinguish from competing electronic excited‐state relaxation channels having similar or even comparable timescales. Here, we report a detailed study on the PSC of a pyrazolate bridged platinum(II) binuclear complex, BFPtPZ (C^NPt(μ‐pz′) 2 PtC^N, C^N=2‐(2,4‐difluorophenyl)pyridine, pz′=pyrazolate), a molecular butterfly, using time‐correlated single photon counting measurements at different wavelengths and sample temperatures. Analysis of the results obtained using dichloromethane (DCM) and ethylene carbonate (EC) as solvents enabled us to reveal an unexpected, strong solvent effect on the PSC processes. We show that a rapid PSC process with a characteristic timescale of 323 ps is observed in DCM, which leads to an excitation equilibrium between the ligand center/metal‐to‐ligand charge transfer ( 3 LC/MLCT) and metal‐metal‐to‐ligand charge transfer ( 3 MMLCT) triplet states. The subsequent relaxation from these electronic states to the ground state takes place in several nanoseconds. In contrast, the corresponding PSC process in EC appears slow at all temperatures studied in our experiments and showed no sign of such excitation equilibrium. The observed solvent effect is found to arise from distinct solvent properties including their viscosities and polarities as well as the peculiar electronic excited‐states of the butterfly‐like molecules with charge transfer character.

Ma, Ying‐Zhong↗
DOE OSTI2022

Superconductor/Ferromagnet Heterostructures: A Platform for Superconducting Spintronics and Quantum Computation

The interplay between superconductivity and ferromagnetism in the superconductor/ferromagnet (SC/FM) heterostructures generates many interesting physical phenomena, including spin-triplet superconductivity, superconducting order parameter oscillation, and topological superconductivity. The unique physical properties make the SC/FM heterostructure as promising platforms for future superconducting spintronics and quantum computation applications. In this article, important research progress of SC/FM heterostructures from superconducting spintronics to quantum computation is reviewed, and it is organized as follows. First, the progress of spin current carriers in SC/FM heterostructures including Bogoliubov quasiparticles, superconducting vortex, and spin-triplet Cooper pairs which might be used for long-range spin transport is discussed. Then, the π Josephson junctions and their application for constructing π qubits are described. Finally, experimental signatures of Majorana states in the SC/FM heterostructures and the theoretically proposed manipulation are briefly reviewed, which could be useful to realize fault-tolerant topological quantum computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Scattering Properties of Ground-State {sup 23}Na Vapor Using Generalized Scattering Theory

The scattering properties of ground-state {sup 23}Na vapor are investigated within the framework of the Galitskii–Migdal–Feynman formalism. Viewed as a generalized scattering theory, this formalism is used to calculate the medium phase shifts. The scattering properties of the system—the total, viscosity, spin-exchange, and average cross sections—are then computed using these phase shifts according to standard recipes. The total cross section is found to exhibit the Ramsauer–Townsend effect as well as resonance peaks. These peaks are caused by the large difference between the potentials for electronic spin-singlet and spin-triplet states. They represent quasi-bound states in the system. The results obtained for the complex spin-exchange cross sections are particularly highlighted because of their importance in the spectroscopy of the Na{sub 2} dimer. So are the results for the scattering lengths pertaining to both singlet and triplet states. Wherever possible, comparison is made with other published results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Fulde–Ferrell State in Spin–Orbit-Coupled Superconductor: Application to Dresselhaus SOC

We show that in the presence of magnetic field, two superconducting phases with the center-of-mass momentum of Cooper pair parallel to the magnetic field are induced in Dresselhaus spin–orbit-coupled superconductor. Specifically, at small magnetic field, the center-of-mass momentum is induced due to the energy-spectrum distortion and no unpairing region with vanishing singlet correlation appears. We refer to this superconducting state as the drift-BCS state. By further increasing the magnetic field, the superconducting state falls into the Fulde–Ferrell state with the emergence of the unpairing regions. The observed abrupt enhancement of the center-of-mass momenta and suppression on the order parameters during the transition indicate the occurrence of a first-order phase transition. Enhanced Pauli limit and hence enlarged magnetic-field regime of the Fulde–Ferrell state, due to the spin-flip terms of the spin–orbit coupling, are revealed. We also address the triplet correlations induced by the spin–orbit coupling, and show that the Cooper-pair spin polarizations, generated by the magnetic field and center-of-mass momentum with the triplet correlations exhibit totally different magnetic-field dependences between the drift-BCS and Fulde–Ferrell states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of the magnetic dipole interaction on a spin-1 system

We consider a hybrid system composed of a spin-1 triplet coupled to a nuclear spin. We study the effect of the axisymmetric and the quadrupole term of the magnetic dipole interaction between the two electrons forming the triplet on the energy spectrum in a static magnetic field. The energy spectrum obtained by directly diagonalizing the Hamiltonian of the system shows that these two terms not only remove the special crossings that appear in the absence of the magnetic dipole interaction, but also produce new (avoided) crossings by lifting the relevant levels. Specially, the gaps between the avoided crossing levels increase with the strength of the quadrupole term. In order to accurately illustrate these effects, we present the results for the discriminant and von Neumann entropy of one electron interacting with the rest of the whole system. Finally, by numerically solving the time-dependent Schrödinger equations of the system, we discover that the polarization oscillation of electron and nuclear spin is in-phase and the total average longitudinal spin is not conserved at location of avoided crossing, but the two results are opposite beyond that.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Computational tools for the simulation and analysis of spin-polarized EPR spectra

The EPR spectra of paramagnetic species induced by photoexcitation typically exhibit enhanced absorptive and emissive features resulting from sublevel populations that differ from thermal equilibrium. The populations and the resulting spin polarization of the spectra are dictated by the selectivity of the photophysical process generating the observed state. Simulation of the spin-polarized EPR spectra is crucial in the characterization of both the dynamics of formation of the photoexcited state as well as its electronic and structural properties. EasySpin, the simulation toolbox for EPR spectroscopy, now includes extended support for the simulation of the EPR spectra of spin-polarized states of arbitrary spin multiplicity and formed by a variety of different mechanisms, including photoexcited triplet states populated by intersystem crossing, charge recombination or spin polarization transfer, spin-correlated radical pairs created by photoinduced electron transfer, triplet pairs formed by singlet fission and multiplet states arising from photoexcitation in systems containing chromophores and stable radicals. In this paper, we highlight EasySpin’s capabilities for the simulation of spin-polarized EPR spectra on the basis of illustrative examples from the literature in a variety of fields ranging across chemistry, biology, material science and quantum information science.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Luminescent lanthanide coordination polymers synthesized via in-situ hydrolysis of dimethyl-3,4-furandicarboxylate

Dimethyl-3,4-furandicarboxylate undergoes hydrolysis under hydrothermal conditions with lanthanide (Ln) ions to form two-dimensional coordination polymers, [Ln(C{sub 6}H{sub 2}O{sub 5})(C{sub 6}H{sub 3}O{sub 5})(H{sub 2}O)]{sub n} (Ln=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). The resulting materials exhibit luminescent properties with quantum yields and lifetimes for the Eu(III) and Tb(III) compounds of 1.1±0.3% and 0.387±0.0001 ms, and 3.3±0.8% and 0.769±0.006 ms, respectively. Energy values for the singlet and triplet states were determined for dimethyl-3,4-furandicarboxylate and 3,4-furandicarboxylic acid. Excited state dynamics and structural features are examined to explicate the reported quantum yields. A series of other FDC structures is briefly presented. - Graphical abstract: A new two-dimensional coordination polymer derived from the in-situ hydrolysis of a furan dimethyl ester with lanthanide(III) ions was obtained in order to study its photophysical behavior when constructed from trivalent Eu and Tb. Quantum yields, lifetime measurements, and singlet/triplet state energies values were obtained. The nature of the material's excited state dynamics is examined and correlated to its structure in order to explain the overall luminescent efficiency of the system. - Highlights: • A new lanthanide–furandicarboxylate coordination polymer is presented. • Eu and Tb compounds display luminescent properties, albeit with low quantum yields. • Photophysical behavior explained through the compound's triplet state and structure. • Nonradiative deactivation of luminescence through high-energy oscillators was noted. • Molecular modeling of the organic moiety was conducted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Singlet Fission and Excimer Formation in Disordered Solids of Alkyl-Substituted 1,3-Diphenylisobenzofurans

Here, we describe the preparation and excited state dynamics of three alkyl derivatives of 1,3-diphenylisobenzofuran (1) in both solutions and thin films. The substitutions are intended to disrupt the slip-stacked packing observed in crystals of 1 while maintaining the favorable energies of singlet and triplet for singlet fission (SF). All substitutions result in films that are largely amorphous as judged by the absence of strong X-ray diffraction peaks. The films of 1 carrying a methyl in the para position of one phenyl ring undergo SF relatively efficiently (≥75% triplet yield, Φ T ) but more slowly than thin films of 1. When the methyl is replaced with a t-butyl, kinetic competition in the excited state favors excimer formation rather than SF (Φ T = 55%). When t-Bu groups are placed in both meta positions of the phenyl substituent, SF is slowed further and Φ T = 35%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Observation of Persistent Zero Modes and Superconducting Vortex Doublets in UTe 2

Superconducting vortices can reveal electron pairing details and nucleate topologically protected states. Yet, vortices of bulk spin-triplet superconductors have never been visualized at the atomic scale. Recently, UTe 2 has emerged as a prime spin-triplet superconductor, but its superconducting order parameter is elusive, and whether time-reversal symmetry (TRS) is broken remains unsettled. Here, in this work, we visualize vortices on the (011) surface of ultraclean UTe 2 single crystals (T c = 2.1 K) using scanning tunneling microscopy (STM). We introduce $\frac{d^{2}𝐼}{d𝑉^{2}}$ imaging as an effective technique for vortex visualization in superconductors with substantial residual zero-energy density of states (DOS), as in UTe 2 . Anisotropic single-flux-quantum vortices, with coherence lengths of ∼12 nm (4 nm) parallel (perpendicular) to the a -axis, form a triangular vortex lattice (VL) under a small out-of-plane magnetic field. The invariance of vortex structures and VL under changes of field polarity and cooling history strongly supports time-reversal invariant superconductivity under zero field. At vortex cores (VCs), nonsplit, spectrally sharp zero-bias conductance peaks (ZBPs) persist up 8 T that are consistent with symmetry-protected Majorana zero modes (MZMs) in a topological vortex line. Close examination of vortex structures reveals a mirror-asymmetric doublet─one with ZBPs and another with an enhanced apparent gap, possibly originating from a field-induced multicomponent order parameter.

UTe2↗
DOE OSTI2016

Two-Photon Absorbing Phosphorescent Metalloporphyrins: Effects of $\pi$-Extension and Peripheral Substitution

The ability to form triplet excited states upon two-photon excitation is important for several applications of metalloporphyrins, including two-photon phosphorescence lifetime microscopy (2PLM) and two-photon photodynamic therapy (PDT). We analyzed one-photon (1P) and degenerate two-photon (2P) absorption properties of several phosphorescent Pt (II) porphyrins, focusing on the effects of aromatic π-extension and peripheral substitution on triplet emissivity and two-photon absorption (2PA). Our 2PA measurements for the first time made use of direct time-resolved detection of phosphorescence, having the ability to efficiently reject laser background through microsecond time gating. π-Extension of the porphyrin macrocycle by way of syn-fusion with two external aromatic fragments, such as in syn-dibenzo- (DBP) and syn-dinaphthoporphyrins (DNP), lowers the symmetry of the porphyrin skeleton. As a result, DBPs and DNPs exhibit stronger 2PA into the one-photon-allowed B (Soret) and Q states than fully symmetric (D 4h ) nonextended porphyrins. However, much more 2P-active states lie above the B state and cannot be accessed due to the interfering linear absorption. Alkoxycarbonyl groups (CO 2 R) in the benzo-rings dramatically enhance 2PA near the B state level. Time-dependent density functional theory (TDDFT) calculations in combinations with the sum-over-states (SOS) formalism revealed that the enhancement is due to the stabilization of higher-lying 2P-active states, which are dominated by the excitations involving orbitals extending onto the carbonyl groups. Furthermore, calculations predicted even stronger stabilization of the 2P-allowed gerade-states in symmetric Pt octaalkoxycarbonyl-tetrabenzoporphyrins. Experiments confirmed that the 2PA cross-section of PtTBP(CO 2 Bu) 8 near 810 nm reaches above 500 GM in spite of its completely centrosymmetric structure. Combined with exceptionally bright phosphorescence (Φ phos = 0.45), strong 2PA makes Pt(II) complexes of π-extended porphyrins a valuable class of chromophores for 2P applications. Another important advantage of these porphyrinoids is their compact size and easily scalable synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Polaron and Exciton Delocalization in Oligomers of High-Performance Polymer PTB7

A key characteristic of organic photovoltaic cells is the efficient charge separation in the active layer. Sufficient delocalization of the positive polaron in organic photovoltaics is considered essential for the effective separation of the opposite charges and the suppression of recombination. Here we use light-induced EPR and ENDOR spectroscopy combined with DFT calculations to determine the electronic structure of the positive polaron in PTB7-type oligomers. Utilizing the superior spectral resolution of high-frequency (130 GHz) D-band EPR, the principal components of the g tensors were determined. Pulsed ENDOR spectroscopy at X-band allowed the measurement of H-1 hyperfine coupling constants. A comparison of g tensors and H-1 hyperfine coupling constants of the PTB7-type oligomers with the high-performance PTB7 polymer revealed a delocalization of the positive polaron in the polymer over about four monomeric units, corresponding to about 45 angstrom in length. Our current study thus not only determines the polaron delocalization length in PTB7 but also validates the approach combining EPR/ENDOR spectroscopy with DFT-calculated magnetic resonance parameters. This is of importance in those cases where oligomers of defined length are not easily obtained. In addition, the delocalization of the neutral triplet exciton was also determined in the oligomers and compared with polymer PTB7. The analysis revealed that the neutral triplet exciton is substantially more delocalized than the positive polaron, exceeding 10 monomeric units.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Dephasing of strong coupling in the non-linear regime

We study the effect of pure dephasing on the strong-coupling of a two-level system (typically, a quantum dot) with the single mode of a microcavity. Whereas dephasing merely broadens the line in the linear regime, it results in a new spectral shape when transitions between higher manifolds of the Jaynes-Cummings ladder are involved, namely, a triplet, that we show does not imply weak-coupling. Higher excitation brings the system into lasing. Description of this intermediate triplet allows to demonstrate quantum nonlinearities even in noisy systems and to measure the magnitude of dephasing.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Hybrid time dependent/independent solution for the He I line ratio temperature and density diagnostic for a thermal helium beam with applications in the scrape-off layer-edge regions in tokamaks

Spectroscopic studies of line emission intensities and ratios offer an attractive option in the development of non-invasive plasma diagnostics. Evaluating ratios of selected He I line emission profiles from the singlet and triplet neutral helium spin systems allows for simultaneous measurement of electron density (n{sub e}) and temperature (T{sub e}) profiles. Typically, this powerful diagnostic tool is limited by the relatively long relaxation times of the {sup 3}S metastable term of helium that populates the triplet spin system, and on which electron temperature sensitive lines are based. By developing a time dependent analytical solution, we model the time evolution of the two spin systems. We present a hybrid time dependent/independent line ratio solution that improves the range of application of this diagnostic technique in the scrape-off layer (SOL) and edge plasma regions when comparing it against the current equilibrium line ratio helium model used at TEXTOR.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Ion imaging study of reaction dynamics in the N{sup +}+ CH{sub 4} system

The velocity map ion imaging method is applied to the ion-molecule reactions of N{sup +} with CH{sub 4}. The velocity space images are collected at collision energies of 0.5 and 1.8 eV, providing both product kinetic energy and angular distributions for the reaction products CH{sub 4}{sup +}, CH{sub 3}{sup +}, and HCNH{sup +}. The charge transfer process is energy resonant and occurs by long-range electron transfer that results in minimal deflection of the products. The formation of the most abundant product, CH{sub 3}{sup +}, proceeds by dissociative charge transfer rather than hydride transfer, as reported in earlier publications. The formation of HCNH{sup +} by C-N bond formation appears to proceed by two different routes. The triplet state intermediates CH{sub 3}NH{sup +} and CH{sub 2}NH{sub 2}{sup +} that are formed as N{sup +}({sup 3}P) approaches CH{sub 4} may undergo sequential loss of two hydrogen atoms to form ground state HCNH{sup +} products on a spin-allowed pathway. However, the kinetic energy distributions for formation of HCNH{sup +} extend past the thermochemical limit to form HCNH{sup +}+ 2H, implying that HCNH{sup +} may also be formed in concert with molecular hydrogen, and requiring that intersystem crossing to the singlet manifold must occur in a significant ({approx}25%) fraction of reactive collisions. We also report GAUSSIAN G2 calculations of the energies and structures of important singlet and triplet [CNH{sub 4}{sup +}] complexes that serve as precursors to product formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Design of large aperture superferric quadrupole magnets for an in-flight fragment separator

Superferric quadrupole magnets to be used for in-flight fragment separator have been designed. A quadrupole magnet triplet for beam focusing is placed in a cryostat together with superconducting correction coils. To maximize acceptance of rare isotope beams produced by projectile fragmentation, it is essential to use large-aperture quadrupole magnets. The pole tip radius is 17 cm in the current design, and we tried to enlarge the aperture with 3D analysis on magnetic fields. In the front end of the separator, where a target and beam dump are located, we plan to use two sets of quadrupole triplets made of high-Tc superconductor (HTS) operating at 20-50 K considering high radiation heat load. The HTS magnet will use warm iron poles. Both low-Tc and high-Tc superconductors are acquired for test winding, and two kinds of dewar and cryostat are under construction to perform the coil and magnet tests. The magnetic design of superferric quadrupole is mainly discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Long-range superconducting proximity effect in polycrystalline Co nanowires

We report experimental evidence of a long-range superconducting proximity effect in polycrystalline Co nanowires in contact with a superconducting W-based floating electrode (inducer). For electrical resistance measurements, voltage leads were connected to the Co nanowire on both sides of the superconducting inducer at a distance of 7.2 μm. We observed a 28% reduction of the nanowire resistance when sweeping the temperature below the inducer's transition temperature T{sub c} = 5.2 K. Our analysis of the resistance data shows that the superconducting proximity length in polycrystalline Co is as large as 1 μm at 2.4 K, attesting to a long-range proximity effect. Moreover, this long-range proximity effect is insusceptible to magnetic fields up to 11 T, which is indicative of spin-triplet pairing. Our results provide evidence that magnetic inhomogeneity of the ferromagnet enlarges the spatial extend of the spin-triplet superconducting proximity effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Coupling and matching study of the ICRF antenna for W7-X

A tight antenna plug consisting in a pair of straps with strong pre-matching covers the first selected frequency band (25-38MHz) for W7-X and provides the toroidal phasings for heating, current drive and wall conditioning. Another plug-in with two short strap triplets is devoted for operation around 76MHz. The antenna coupling to a reference plasma profile is first analyzed by means of the coupling code ANTITER II. It shows the radiation power spectra for the different phasing cases and indicates the problem of the edge power deposition through the Alfven resonance occurring when the operating frequency is lower than the majority cyclotron frequency. Matrices provided by the TOPICA code are used for the matching-decoupling study of the first antenna plug. The large mutual coupling between the 2 straps is counterbalanced by the use of a decoupler. Finally the tunable 5-port junction used to feed in parallel each triplet of the second plug-in is analyzed by means of MWS simulation together with its decoupling-matching system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Thermo-structural development of the ITER ICRF strap housing module

Since March 2010 the preliminary design of the ITER ICRF Antennas have been developed by CYCLE, a consortium consisting of IPP (Garching), CCFE (Culham), CEA (Cadarache), Politecnico di Torino (Torino) and LPPERM/KMS (Brussels). This paper describes the steps taken to develop the present geometry of the triplet pair Strap Housing Module from a thermal and structural perspective, and shows the critical areas of the structure. Key issues are the manufacturability, (achieved by HIPing - Hot Isostatic Pressing), the ability to handle the radiating plasma thermal flux of 0.35 MW/m{sup 2}, the RF losses and the neutronic radiation. HIPing is necessary to achieve the complicated system of cooling channels inside the structure, which divides the coolant equally in order to supply each strap in the triplet with 1 l/s of water. The components have also to withstand the strong mechanical forces generated by plasma disruptions affecting all internal structures and the elevated design cooling water pressure of 5MPa. In order to maximise reliability, joints between different materials in the cooling water system have been kept to a minimum. Therefore, in the interests of fabricability and availability, the whole structure is manufactured out of stainless steel (316L(N)IG). The low conductivity of 316L(N)IG demands small wall thicknesses to avoid hot spots; however this reduces the mechanical strength. Consequently an in depth FEM analysis is presented, which was used to find and to improve the critical aspects of this important component and was the best means of finding the optimum between thermal and mechanical performance.

42 ENGINEERING↗