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All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Emergent Ising degrees of freedom above a double-stripe magnetic ground state [Emergent Ising degrees of freedom above double-stripe magnetism]

Here, double-stripe magnetism [Q=(π/2,π/2)] has been proposed as the magnetic ground state for both the iron-telluride and BaTi 2 Sb 2 O families of superconductors. Double-stripe order is captured within a J 1 –J 2 –J 3 Heisenberg model in the regime J 3 >> J 2 >> J 1 . Intriguingly, besides breaking spin-rotational symmetry, the ground-state manifold has three additional Ising degrees of freedom associated with bond ordering. Via their coupling to the lattice, they give rise to an orthorhombic distortion and to two nonuniform lattice distortions with wave vector (π,π). Because the ground state is fourfold degenerate, modulo rotations in spin space, only two of these Ising bond order parameters are independent. Here, we introduce an effective field theory to treat all Ising order parameters, as well as magnetic order, and solve it within a large-N limit. All three transitions, corresponding to the condensations of two Ising bond order parameters and one magnetic order parameter are simultaneous and first order in three dimensions, but lower dimensionality, or equivalently weaker interlayer coupling, and weaker magnetoelastic coupling can split the three transitions, and in some cases allows for two separate Ising phase transitions above the magnetic one.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

DETECTING GRAVITATIONAL WAVE MEMORY WITH PULSAR TIMING

We compare the detectability of gravitational bursts passing through the solar system with those passing near each millisecond pulsar in an N-pulsar timing array. The sensitivity to Earth-passing bursts can exploit the correlation expected in pulse arrival times while pulsar-passing bursts, though uncorrelated between objects, provide an N-fold increase in overall time baseline that can compensate for the lower sensitivity. Bursts with memory from mergers of supermassive black holes produce step functions in apparent spin frequency that are the easiest to detect in pulsar timing. We show that the burst rate and amplitude distribution, while strongly dependent on inadequately known cosmological evolution, may favor detection in the pulsar terms rather than the Earth timing perturbations. Any contamination of timing data by red spin noise makes burst detection more difficult because both signals grow with the length of the time data span T. Furthermore, the different bursts that could appear in one or more data sets of length T Almost-Equal-To 10 yr also affect the detectability of the gravitational wave stochastic background that, like spin noise, has a red power spectrum. A burst with memory is a worthwhile target in the timing of multiple pulsars in a globular cluster because it should produce a correlated signal with a time delay of less than about 10 years in some cases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Experimental evidence for the two-path description of neutron spin echo

Here, we describe an experiment that strongly supports a two-path interferometric model in which the spin-up and spin-down components of each neutron propagate coherently along spatially separated parallel paths in a typical neutron spin-echo small-angle scattering (SESANS) experiment. Specifically, we show that the usual semi-classical, single-path treatment of Larmor precession of a polarized neutron in an external magnetic field predicts a damping as a function of the spin-echo length of the SESANS signal obtained with a periodic phase grating when the transverse width of the neutron wave packet is finite. However, no such damping is observed experimentally, implying either that the Larmor model is incorrect or that the transverse extent of the wave packet is very large. In contrast, we demonstrate theoretically that a quantum-mechanical interferometric model in which the two mode-entangled (i.e., intraparticle entangled) spin states of a single neutron are separated in space when they interact with the grating accurately predicts the measured SESANS signal, which is independent of the wave packet width.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Electronic structure and magnetism of Mn-doped GaSb for spintronic applications: A DFT study

We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x = 0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the Mn{sub Ga} substitution is the most stable configuration with a formation energy of ∼1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 μ{sub B}/Mn-atom. The results indicate that the magnetic ground state originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Prediction of Half-Metallic Properties in Non-transition Metal-based Binary Compounds X Bi (X = Ba, Sr and Ca) with Zinc-Blende and Wurtzite Structures

In this study, structural, electronic and magnetic properties of non-transition metal-based binary compounds X Bi (X = Ba, Sr and Ca) in five different phases: rock salt, NiAs, wurtzite, zinc blende and CsCl, are investigated in order to find new sp magnetic materials used for real spintronic and other related applications. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW + lo) method within the spin density functional theory. As exchange-correlation potential, we used the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) and the modified Becke-Johnson potential mBJ-GGA-PBE form. It is found that the magnetic moment in these compounds is mainly contributed by the spin-polarized p orbitals of Bi atoms. The WZ XBi are true half-metallic ferromagnet with opposite spin direction at Fermi energy having a magnetic moment of 2.00 μ B per formula unit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spin–Orbit Coupling Constants in Atoms and Ions of Transition Elements: Comparison of Effective Core Potentials, Model Core Potentials, and All-Electron Methods

The spin–orbit coupling constants (SOCC) in atoms and ions of the first- through third-row transition elements were calculated for the low-lying atomic states whose main electron configuration is [ n d] q ( q = 1–4 and 6–9, n = the principal quantum number), using four different approaches: (1) a nonrelativistic Hamiltonian used to construct multiconfiguration self-consistent field (MCSCF) wave functions utilizing effective core potentials and their associated basis sets within the framework of second-order configuration interaction (SOCI) to calculate spin–orbit couplings (SOC) using one-electron Breit–Pauli Hamiltonian (BPH), (2) a nonrelativistic Hamiltonian used to construct MCSCF wave functions utilizing model core potentials and their associated basis sets within the framework of SOCI to calculate SOC using the full BPH, (3) nonrelativistic and spin-independent relativistic Hamiltonians used to construct MCSCF wave functions utilizing all-electron (AE) basis sets within the framework of SOCI to calculate SOC using the full BPH, and (4) a relativistic Hamiltonian given by the exact two-component (X2C) transformation for construction of Kramers-restricted relativistic configuration interaction wave functions. In this investigation, these four approaches are referred to as ECP, MCP, AE, and X2C methods, respectively. The ECP, MCP, and AE methods are so-called two-step approaches (TSA), while the X2C method is a one-step approach (OSA). In the AE method, three different calculations—relativistic elimination of small components (RESC), third-order Douglas–Kroll–Hess (DKH3), and infinite-order two-component (IOTC) relativistic correction—were performed for the estimation of the scalar relativistic components in addition to those of the nonscalar relativistic (NSR) contributions. The calculated SOCC are compared to the available experimental data via the Landé interval rule. Although there are several exceptions, including states whose main configuration is [ n d] 5 , the average differences between the ECP and AE (IOTC) SOCC and between the ECP and the X2C SOCC are mostly less than 20%. The differences between the ECP and the experimental SOCC are even smaller. No serious discrepancy was found between the TSA and OSA predictions of SOCC for the first- and second-row transition elements in comparison to experiment. For atoms and ions of the third-row transition elements, the SOCC calculated through the Landé interval rule are not reliable. The low-energy spin-mixed (SM) states originating from a [5d]q configuration ( q = 2–4) have a larger energy lowering due to the SOC effects, in comparison with those for atoms and ions of the first- and second-row transition elements. For the spin-mixed (SM) states originating from a [5d]q configuration ( q = 6–8), the energy lowering of all 4 F 7/2 , 5 D 1 , and 5 D 3 states due to the SOC effects is smaller than those of the other SM states. Furthermore this difficulty, which also arises for the MCP, AE, and X2C (OSA) approaches, suggests that the LS-coupling scheme is inappropriate.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Two-leg SU ( 2 n ) spin ladder: A low-energy effective field theory approach

We present a field-theory analysis of a model of two SU( 2n )-invariant magnetic chains coupled by a generic interaction preserving time reversal and inversion symmetry. Contrary to the SU(2)-invariant case the zero-temperature phase diagram of such two-leg spin ladder does not contain topological phases. Thus, only generalized Valence Bond Solid phases are stabilized when n > 1 with different wave vectors and ground-state degeneracies. In particular, we find a phase which is made of a cluster of 2n spins put in an SU( 2n ) singlet state. For n = 3, this cluster phase is relevant to ¹⁷³Yb ultracold atoms, with an emergent SU(6) symmetry, loaded in a double-well optical lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Communication: Configuration interaction combined with spin-projection for strongly correlated molecular electronic structures

We present single and double particle-hole excitations in the recently revived spin-projected Hartree-Fock. Our motivation is to treat static correlation with spin-projection and recover the residual correlation, mostly dynamic in nature, with simple configuration interaction (CI). To this end, we introduce the Wick theorem for nonorthogonal determinants, which enables an efficient implementation in conjunction with the direct CI scheme. The proposed approach, termed spin-extended CI with singles and doubles, achieves a balanced treatment between dynamic and static correlations. To approximately account for the quadruple excitations, we also modify the well-known Davidson correction. We report that our approaches yield surprisingly accurate potential curves for HF, H{sub 2}O, N{sub 2}, and a hydrogen lattice, compared to traditional single reference wave function methods at the same computational scaling as regular CI.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Nature of the magnetic stripes in fully oxygenated La 2 CuO 4+y

We present triple-axis neutron scattering studies of static and dynamic magnetic stripes in an optimally oxygen-doped cuprate superconductor, La 2 CuO 4+y , which exhibits a clean superconducting transition at T c = 42 K. Polarization analysis reveals that the magnetic stripe structure is equally represented along both of the tetragonal crystal axes and that the fluctuating stripes display significant weight for in-plane as well as out-of-plane spin components. Both static magnetic order as well as low-energy fluctuations are fully developed in zero applied magnetic field and the low-energy spin fluctuations at ℏω = 0.3 – 10 meV intensify on cooling. We interpret this as an indication that superconductivity and low-energy spin fluctuations coexist microscopically in spatial regions which are separated from domains with static magnetic order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Primordial gravitational waves from black hole evaporation in standard and nonstandard cosmologies

Gravitons radiated from light, evaporating black holes contribute to the stochastic background of gravitational waves. The spectrum of such emission depends on both the mass and the spin of the black holes, as well as on the redshifting that occurs between the black hole formation and today. This, in turn, depends on the expansion history of the Universe, which is largely unknown and unconstrained at times prior to the synthesis of light elements. Here, we explore the features of the stochastic background of gravitational waves from black hole evaporation under a broad range of possible early cosmological histories. The resulting gravitational wave signals typically peak at very high frequencies, and offer opportunities for proposed ultrahigh-frequency gravitational wave detectors. Lower-frequency peaks are also possible, albeit with a suppressed intensity that is likely well below the threshold of detectability. We find that the largest intensity peaks correspond to cosmologies dominated by fluids with equations of state that have large pressure-to-density ratios. Such scenarios can be constrained on the basis of violation of Δ⁢N eff bounds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Spin and parity measurement of the Λ(1405) baryon

A determination of the spin and parity of the Λ(1405) is presented using photoproduction data from the CLAS detector at Jefferson Lab. The reaction γ+p→K + +Λ(1405) is analyzed in the decay channel Lambda(1405)→Σ + +π, where the decay distribution to Σ + pi- and the variation of the Σ + polarization with respect to the Λ(1405) polarization direction determines the parity. The Λ(1405) is produced, in the energy range 2.55 c.m. K+ <0.9, with polarization P=0.45±0.02(stat)±0.07(syst). The analysis shows that the decays are in S wave, with the Σ + polarized such that the Λ(1405) has spin-parity J P =1/2-, as expected by most theories.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Emergent superconductivity in topological-kagome-magnet/metal heterostructures

Itinerant kagome lattice magnets exhibit many novel correlated and topological quantum electronic states with broken time-reversal symmetry. Superconductivity, however, has not been observed in this class of materials, presenting a roadblock in a promising path toward topological superconductivity. Here, we report that novel superconductivity can emerge at the interface of kagome Chern magnet TbMn 6 Sn 6 and metal heterostructures when elemental metallic thin films are deposited on either the top (001) surface or the side surfaces. Superconductivity is also successfully induced and systematically studied by using various types of metallic tips on different TbMn 6 Sn 6 surfaces in point-contact measurements. The anisotropy of the superconducting upper critical field suggests that the emergent superconductivity is quasi-two-dimensional. Remarkably, the interface superconductor couples to the magnetic order of the kagome metal and exhibits a hysteretic magnetoresistance in the superconducting states. Taking into account the spin-orbit coupling, the observed interface superconductivity can be a surprising and more realistic realization of the p-wave topological superconductors theoretically proposed for two-dimensional semiconductors proximity-coupled to s-wave superconductors and insulating ferromagnets. Our findings of robust superconductivity in topological-Chern-magnet/metal heterostructures offer a new direction for investigating spin-triplet pairing and topological superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Domain Structure and Magnetization Reversal Micromechanisms in Quasi-Two-Dimensional Exchange-Biased Nanomagnetics

Abstract—The domain structure and magnetization reversal mechanisms are studied in quasi-two-dimensional exchange-biased NiFe/FeMn and NiFe/NiO nanomagnetics, using a complex method of magnetooptical indicator films and acoustic emission. The presence of the axial dispersion of unidirectional anisotropy in grains of the antiferromagnetic layer is shown to determine the statistic distribution and chirality of spin springs near the interface. The acoustic emission signals caused by the excitation of elastic Lamb waves upon the magnetization reversal of NiFe/NiO heterostructure are found. The coercive force of these systems is due to irreversible processes to overcome potential barriers that are induced by the formation of spin springs with different chirality, localized in the antiferromagnetic near the ferromagnetic–antiferromagnetic boundary.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Spinning metasurface stack for spectro-polarimetric thermal imaging

Spectro-polarimetric imaging in the long-wave infrared (LWIR) region plays a crucial role in applications from night vision and machine perception to trace gas sensing and thermography. However, the current generation of spectro-polarimetric LWIR imagers suffers from limitations in size, spectral resolution, and field of view (FOV). While meta-optics-based strategies for spectro-polarimetric imaging have been explored in the visible spectrum, their potential for thermal imaging remains largely unexplored. In this work, we introduce an approach for spectro-polarimetric decomposition by combining large-area stacked meta-optical devices with advanced computational imaging algorithms. The co-design of a stack of spinning dispersive metasurfaces along with compressive sensing and dictionary learning algorithms allows simultaneous spectral and polarimetric resolution without the need for bulky filter wheels or interferometers. Our spinning-metasurface-based spectro-polarimetric stack is compact (<10×10×10cm) and robust, and it offers a wide field of view (20.5°). We show that the spectral resolving power of our system substantially enhances performance in machine learning tasks such as material classification, a challenge for conventional panchromatic thermal cameras. Our approach represents a significant advance in the field of thermal imaging for a wide range of applications including heat-assisted detection and ranging (HADAR).

Optics↗
DOE OSTI2014

Cosmological magnetic fields as string dynamo seeds and axion fields in torsioned spacetime

In this paper two examples of the generation cosmological magnetic fields (CMF) are given. The first is the string dynamo seed cosmological magnetic field estimated as B{sub seed}∼10{sup -24} Gauss from a static spin polarised cylinder in Einstein-Cartan-Maxwell spacetime. The string dynamo seeds from a static spin polarised cylinder is given by B∼σ{sup 2}R{sup 2} where σ is the spin-torsion density while R is the string radius. The B-field value above is able to seed galactic dynamo. In the BBN the magnetic fields around 10{sup 12} Gauss give rise to a string radius as small as 10{sup 17}l{sub P} where l{sub P} is the Planck length. The second is the CMF from axionic torsion field which is given by B{sub seed}∼10{sup -27} Gauss which is stronger than the primordial magnetic field B{sub BICEP2}∼10{sup -30} Gauss from the BICEP2 recent experiment on primordial gravitational waves and cosmological inflation to axionic torsion. The interaction Lagrangean between axionic torsion scalar φ and magnetic fields used in this last example is given by f{sup 2}(φ)F{sub μν}F{sup μν}. A similar lagrangean has been used by K. Bamba et al. [JCAP 10 (2012) 058] so generate magnetic fields without dynamo action. Since axionic torsion can be associated with axionic domain walls both examples discussed here could be consider as topological defects examples of the generation of primordial magnetic fields in universes endowed with spacetime torsion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Nodeless High- T c Superconductivity in the Highly Overdoped CuO 2 Monolayer

We study the electronic structure and superconductivity in a CuO 2 monolayer grown recently on the d-wave cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ . Density functional theory calculations indicate a significant charge transfer across the interface such that the CuO 2 monolayer is heavily overdoped into the hole-rich regime yet inaccessible in bulk cuprates. We show that both the Cu d x 2 –y 2 and d 3z 2 –r 2 orbitals become important and the Fermi surface contains one electron and one hole pocket associated with the two orbitals, respectively. Constructing a minimal correlated two-orbital model for the e g complex, we show that the spin-orbital exchange interactions produce a nodeless superconductor with extended s-wave pairing symmetry and a pairing energy gap comparable to the bulk d-wave gap, in agreement with recent experiments. Here, the findings point to a direction of realizing new high-T c superconductors in ozone grown transition-metal-oxide monolayer heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Energetic Electron Precipitation Driven by Electromagnetic Ion Cyclotron Waves from ELFIN’s Low Altitude Perspective

We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data collected by the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at >0.5 MeV which are abrupt (bursty) (lasting ~17 s, or ΔL ~ 0.56) with significant substructure (occasionally down to sub-second timescale). We attribute the bursty nature of the precipitation to the spatial extent and structuredness of the wave field at the equator. Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Case studies employing conjugate ground-based or equatorial observations of the EMIC waves reveal that the energy of moderate and strong precipitation at ELFIN approximately agrees with theoretical expectations for cyclotron resonant interactions in a cold plasma. Using multiple years of ELFIN data uniformly distributed in local time, we assemble a statistical database of ~50 events of strong EMIC wave-driven precipitation. Most reside at L ~ 5 – 7 at dusk, while a smaller subset exists at L ~ 8 – 12 at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an L-shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio’s spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of ~ 1.45 MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. It should be noted though that this diffusive treatment likely includes effects from nonlinear resonant interactions (especially at high energies) and nonresonant effects from sharp wave packet edges (at low energies). Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven >1 MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to ~ 200-300 keV by much less intense higher frequency EMIC waves at dusk (where such waves are most frequent). At ~100 keV, whistler-mode chorus may be implicated in concurrent precipitation. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Measurements of Siple transmitter signals on the DE 1 satellite - Wave normal direction and antenna effective length

A new experimental technique is developed to simultaneously measure the wave propagation direction and the effective length of a small (L value much smaller than wavelength) electric dipole antenna on a spin-stabilized satellite in the magnetosphere. The technique relies on the near simultaneous measurement of single components of the electric and magnetic fields of a coherent VLF signal injected into the medium from a ground-based source. The spin fading characteristics of the signal received by the electric dipole and the magnetic loop antenna permit the measurement of the wave normal direction assuming whistler-mode propagation. In-situ and remote measurements of the local cold plasma density are used to determine the refractive index. The wave electric field is then inferred from the wave magnetic field as measured on the loop antenna, the refractive index and the direction of propagation. Comparing this electric field with the measured voltage across the dipole antenna leads to the determination of the effective length of the receiving electric dipole. The technique is applied to data from the Dynamics Explorer 1 satellite observations of whistler mode signals injected into the magnetosphere from the Siple, Antarctica, VLF transmitter. In one case, with the measured background cold plasma density being 15 el/cu cm, the effective length of the 200 m-long electric dipole antenna is found to be 222 + or - 56 m, i.e., about twice the conventional value.

Sonwalker, V. S.↗

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