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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Spin excitations and dynamics in 2D magnets: An overview of magnons and magnetic skyrmions

van der Waals magnetic materials open up exciting possibilities to investigate fundamental spin properties in low-dimensional systems and to build compact functional spintronic structures. This review focuses on the recent progress in two-dimensional (2D) magnets that explore beyond the homogenous magnetically ordered state, including magnons (spin waves), magnetic skyrmions, and complex magnetic domains. Properties of these spin and topology excitations in 2D magnets provide insights into spin-orbit interactions and other forms of coupling between electrons, phonons, and spin-dependent excitations. Such spin-based quasiparticles can also serve as information carriers for next-generation high-speed computing elements. Furthermore, we will first lay out the general theoretical basis of dynamical responses in magnetic systems, followed by detailed descriptions of experimental progress in magnons and spin textures (including magnetic domains and skyrmions). Discussion on the experimental techniques and future perspectives are also included.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Classical dynamics of the antiferromagnetic Heisenberg spin ladder

We employ a classical limit grounded in SU(4) coherent states to investigate the temperature-dependent dynamical spin structure factor of the S = 1/2 ladder consisting of weakly coupled dimers. By comparing the outcomes of this classical approximation with density matrix renormalization group and exact diagonalization calculations in finite size ladders, we demonstrate that the classical dynamics offers an accurate approximation across the entire temperature range when the interdimer coupling is weak and a good approximation in the high temperature regime even when the interdimer coupling is strong. This agreement is achieved after appropriately rescaling the temperature axis and renormalizing expectation values to satisfy a quantum sum rule. Here, we anticipate the method will be particularly effective when applied to 2D and 3D lattices composed of weakly-coupled dimers, situations that remain challenging for alternative numerical methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Realtime dynamics of hyperon spin correlations from string fragmentation in a deformed four-flavor Schwinger model

Self-polarizing weak decays of Λ -hyperons provide unique insight into the role of entanglement in the fragmentation of QCD strings through measurements of the spin correlations of Λ Λ ¯ pairs produced in collider experiments. The simplest quantum field theory representing the underlying parton dynamics is the four-flavor massive Schwinger model plus an effective spin-flip term, where the flavors are mapped to light (up or down) and heavy (strange) quarks and their spins. This construction provides a novel way to explore hyperon spin correlations in 1 + 1 dimensions. We investigate the evolution of these correlations for different string configurations that are sensitive to the rich structure of the model Hamiltonian. Published by the American Physical Society 2024

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Bridge Connectivity Dictates Spin Interactions and Triplet Pair Dynamics in Intramolecular Singlet Fission

Electron spin plays a critical role in determining the structure, dynamics, and reactivities of molecular excited states, including multiexciton processes such as singlet fission. These systems exhibit triplet pair states whose excited state dynamics can be widely tuned through molecular engineering. For example, the electronic coupling between covalently linked chromophores can be readily modulated using chemical bridges to control proximity, quantum interference, or resonance effects. However, less is known about how spin coupling interactions are impacted by chromophore architecture, and how this influences triplet pair recombination dynamics. Here, in this study, we investigate the role of bridge connectivity and chromophore identity in modulating interchromophore exchange and dipolar coupling interactions for a series of pentacene and tetracene dimers bridged by alternant hydrocarbons (phenylene, naphthalene, anthracene). Using both time-resolved electron paramagnetic resonance and transient absorption spectroscopy, we find that the boundedness and recombination pathways of the triplet pair spins are highly sensitive to molecular architecture and chromophore-specific magnetic dipolar interactions. Notably, nominally ferromagnetic and antiferromagnetic eigenstates result in distinct spin state orderings, consistent with predictions from quantum interference-based graphical models. These findings establish new design principles for tuning spin dynamics in iSF materials, with implications for photonic and quantum information applications.

He, Guiying [City Univ. of New York (CUNY), NY (Un↗
DOE OSTI2024

Spin and lattice dynamics of the two-dimensional van der Waals ferromagnet CrI3

Chromium tri-iodide (CrI 3 ) is a prototypical ferromagnetic van der Waals insulator with its genuinely two-dimensional (2D) long-range magnetic order below 45 K demonstrated recently. The underlying magnetic anisotropy has not been completely understood while both the Dzyaloshinskii-Moriya (DM) interaction and the Kitaev—Γ type interaction have been considered as the relevant magnetic Hamiltonian. In addition, the relation between the crystal structure and the magnetic order needs to be further elucidated concerning their possible coupling in few-layer samples and in the topmost surface layers of bulk samples. Here, we investigate these issues via temperature- and magnetic field-dependent terahertz spectroscopy on bulk CrI 3 single crystals, focusing on the dynamics of ferromagnetic resonances (FMRs) and optical phonons in the terahertz (THz) region from 4 to 120 cm -1 (from 0.5 to 15 meV). We narrow down the possible ranges of the interaction parameters such as the off-diagonal symmetric terms and the single-ion anisotropy. The accurate values of these parameters significantly constrain the magnitude of possible Kitaev—Γ exchange interaction and the topological magnon gap. Moreover, the structure-magnetism relationship was critically analyzed based on the temperature- and field-dependences of two E u in-plane optical phonon modes, which shows that the commonly believed structural phase diagram of CrI 3 , derived from surface-preferential data, has to be seriously modified.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Classical signatures of quenched and thermal disorder in the dynamics of correlated spin systems

Neutron scattering is frequently used to look for evidence of features indicative of quantum-entangled phases of matter such as continua from fractionalisation or quantised excitations. However, the non-specificity of these features and difficulty of both fully quantum treatments and semiclassical models of disorder, make the diagnosis of such states problematic. Here, we demonstrate the feasibility of semiclassical treatments of disordered systems for supercells of ~10 000 spins. By examining a number of classically disordered models we show the presence of quantised excitations, broad continua and anomalous damping originating from quenched disorder or large classical degeneracies.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Phonon dynamics in quantum spin liquid and valence bond crystal states in the barlowite family of kagome magnets

The barlowite [Cu 4 ⁢(OD) 6⁢ FBr] family of materials is characterized by antiferromagnetic spin-1/2 kagome layers and are believed to host interesting ground states of quantum magnetism. Substituting the interlayer sites with zinc ions yields Zn-barlowite (Zn 𝑥 ⁢Cu 4−𝑥 ⁢(OD) 6 ⁢FBr, 𝑥 ≈ 0.80) which is a strong candidate to have a quantum spin liquid (QSL) state. Experimentally distinguishing between valence bond crystal (VBC) and QSL states in the absence of magnetic ordering can prove challenging as both states exhibit similar average spin-spin correlations. Using high-resolution inelastic x-ray scattering with 1.4 meV energy resolution, we probe acoustic phonons in these structurally similar materials at various temperatures. Our measurements uncover robust differences possibly driven by different spin-phonon physics in VBC and QSL states, particularly at the 𝑀-point Brillouin zone boundary. Over a large 𝑇=[15,200]⁢ K temperature range, where neither material undergoes magnetic ordering nor a structural transition, we observe phonon softening in Zn-barlowite in contrast to a hardening of the same phonon in barlowite. Further, these results indicate that acoustic phonons in the barlowite system can be used to study and possibly distinguish between QSL and disordered VBC states in quantum magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Cluster spin glass correlations and dynamics in Zn 0.5⁢ Mn 0.5⁢ Te

Here, we present a combined magnetometry, muon spin-relaxation (𝜇⁢SR), and neutron-scattering study of the insulating spin glass Zn 0.5 ⁢Mn 0.5 ⁢Te, for which magnetic Mn 2+ and nonmagnetic Zn 2+ ions are randomly distributed on a face-centered cubic lattice. The magnetometry and 𝜇⁢SR results confirm a spin freezing transition around 𝑇 𝑓 ≈ 23 K, with the spin-fluctuation rate decreasing gradually and somewhat inhomogeneously through the sample volume as the temperature decreases toward 𝑇 𝑓 . Characteristic spin-correlation times well above 𝑇 𝑓 are on the order of 10 −10 s, much slower than typically observed in canonical spin glasses but in line with expectations for a cluster spin glass. Using magnetic pair distribution function (mPDF) analysis and reverse Monte Carlo (RMC) modeling of the magnetic diffuse neutron-scattering data, we show that the spin-glass ground state consists of clusters of spins exhibiting short-range-ordered type-III antiferromagnetic correlations with a locally ordered moment of 3.1⁢(1)⁢𝜇 B between nearest-neighbor spins. The type-III correlations decay exponentially as a function of spin separation distance with a correlation length of approximately 5 Å. The diffuse magnetic scattering and corresponding mPDF show no significant changes across 𝑇 𝑓 , indicating that the dynamically fluctuating short-range spin correlations in the paramagnetic state retain the same basic type-III configuration that characterizes the spin-glass state; the only change apparent from the neutron-scattering data is a gradual reduction of the correlation length and locally ordered moment with increasing temperature. Taken together, these results paint a unique and detailed picture of the local magnetic structure and dynamics in Zn 0.5 ⁢Mn 0.5⁢ Te and provide strong evidence that this material is best described as a cluster spin glass. In addition, this work showcases a statistical method for extracting diffuse scattering signals from neutron powder diffraction data, which we developed to facilitate the mPDF and RMC analysis of the neutron data. This method has the potential to be broadly useful for neutron powder diffraction experiments on a variety of materials with short-range atomic or magnetic order.

magnetism↗
DOE OSTI2026

Classification of dynamical Lie algebras generated by spin interactions on undirected graphs

Dynamical Lie algebras (DLAs) are a versatile tool for various topics that span from the expressibility-trainability of variational quantum algorithms (VQAs), to simulation of many body Hamiltonians. Quantum gates and most of the Hamiltonians of interest consist of local interactions; therefore, the analysis of all possible DLAs generated by 1- and 2-local operators is crucial for quantum simulation and VQAs on current hardware. Previously in [R. Wiersema et al ., npj Quantum Inf. 10 , 110 (2024)], we analyzed the DLAs on linear, circular and all-to-all topologies, and obtained results about their dimensions and algebraic structure. Here, in this work, we extend our analysis into any possible hardware topology and provide a classification of all DLAs generated by Pauli strings on any undirected interaction graph. Our results indicate that the DLAs depend solely on whether the connectivity or interaction graph is bipartite or not. In addition, we find that the non-trivial polynomially scaling DLAs appear only on 1D line or circle topologies, and all other DLAs have dimensions scaling exponentially with the system size. Together with the current VQA literature, our results imply that either the majority of VQAs are non-trainable, or we are yet to understand the role of DLAs on the trainability of VQAs.

Algebraic structures↗
DOE OSTI2026

Magnetic resonance control of spin-correlated radical pair dynamics in vivo

Magnetic fields can influence reactions involving spin-correlated radical pairs (SCRPs). This provides a mechanism by which both static and time-varying magnetic fields can affect living systems at the biomolecular level. However, an engineered SCRP system conferring magnetic sensitivity to a non-native biochemical process in a multicellular organism has not yet been demonstrated. Here, in this study, we demonstrate control of SCRP dynamics using magnetic resonance in a live transgenic animal. We show that the emission of various red fluorescent proteins (RFPs), in the presence of a flavin cofactor, can be modified by a combination of static and radiofrequency magnetic fields applied near the electron spin resonance frequency. This effect was measured at room temperature both in vitro and in the nematode Caenorhabditis elegans, genetically modified to express the RFP mScarlet. These observations suggest that the magnetic field effects measured in RFP-flavin systems are due to quantum-correlated radical pairs with a coherence time larger than 4 ns. Our experiments demonstrate that radiofrequency magnetic fields can influence dynamics of reactions involving SCRPs in vivo, potentially enabling new methods for remotely controlling biomolecular processes, such as gene expression, and suggest broader potential for quantum tools in biology.

Burd, Shaun C. [Stanford Univ., CA (United States)↗
DOE OSTI2026

Enhancement of antiferromagnetic spin fluctuations in UTe2 under pressure revealed by 125 Te NMR

Characterizing magnetic fluctuations is one of the keys to understanding the origin of superconductivity in the spin-triplet superconductor UTe 2 , which exhibits two superconducting (SC) phases (SC1 and SC2) under pressure: SC1 where the superconducting transition temperature of 𝑇c decreases with pressure, whereas 𝑇c of SC2 rises with pressure. Previously, D. Ambika et al. [Phys. Rev. B 105, L220403 (2022)] reported the possible coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) spin fluctuations in UTe2 under pressure from their nuclear magnetic resonance (NMR) measurements. To delve into the relationship between the magnetic fluctuations and the two SC phases, we have carried out detailed 125 Te NMR measurements on a single crystal of UTe2 with 𝑇c=1.6K at various pressures ranging from 0 to 2.05 GPa. By comparing the temperature 𝑇 dependence of nuclear spin-lattice relaxation rates divided by temperature 1/𝑇1⁢𝑇 with that of the Knight shift 𝐾 for magnetic fields along the 𝑎, 𝑏, and 𝑐 directions, we evidence the enhancement of AFM spin fluctuations with increasing pressure. Based on the results, we suggest that FM spin fluctuations are more favorable for SC1 and AFM spin fluctuations are crucial for SC2. Our work will inspire further study on this material to understand the peculiar SC phases in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Weyl semimetal phases and intrinsic spin-Hall conductivity in SbAs ordered alloys

Here, using density functional theory calculations, we investigated possible Weyl semimetal (WSM) phases in antimony arsenide ordered alloys Sb 1-x ⁢As x (x=0, 1/6, 1/3, 1/2, 2/3, 5/6, 1). We find WSM phases for all As compositions of Sb 1-x ⁢As x with broken inversion symmetry, in contrast to Bi 1-x⁢ Sb x where only compositions x=1/2 and 5/6 were predicted to exhibit WSM phases. The WSM phases in Sb 1-x ⁢As x are characterized by the presence of 12 Weyl points, located within 55 meV from the Fermi level in the case of x = 1/2. The robust spin-orbit coupling strength and Berry curvature in these alloys produce large spin-Hall conductivity in the range of 176–602 ($\hslash$/e)(S/cm), comparable to that in the BiSb alloys. Finally, Sb 0.5 ⁢As 0.5 is predicted to be almost lattice matched to GaAs(111), with the Fermi level within the gap of the semiconductor, facilitating growth and characterization, and thus, offering promising integration with conventional semiconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Phonon dynamics in the chiral Kitaev spin liquid

Here, we investigate the effect of a magnetic field on the extended Kitaev spin-liquid state through phonon dynamics. Using a constrained fermionic self-consistent mean field method, we analyze the quantum spin liquid (QSL) ground state for the extended Kitaev model with both the Zeeman term and the perturbative three-spin interaction term 𝜅. Our results demonstrate the dependence of the stability of the Kitaev QSL state on the field direction, consistent with findings in the literature. Additionally, we calculate the phonon dynamics for acoustic phonons coupled to the Majorana fermion excitations of the Kitaev spin-liquid state, discussing the temperature and field evolution of these quantities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Correlated spin-wave generation and domain-wall oscillation in a topologically textured magnetic film

Spin waves, or magnons, are essential for next-generation energy-efficient spintronics and magnonics. Yet, visualizing spin-wave dynamics at nanoscale and microwave frequencies remains a formidable challenge due to the lack of spin-sensitive, time-resolved microscopy. Here, in this study, we report a breakthrough in imaging dipole-exchange spin waves in a ferromagnetic film owing to the development of laser-free ultrafast Lorentz electron microscopy, which is equipped with a microwave-mediated electron pulser for high spatiotemporal resolution. Using topological spin textures, we captured the emission, propagation, reflection and interference of spin waves from spin anti-vortices under radio-frequency excitations. Remarkably, we show that spin-wave generation is closely tied to the oscillatory motion of specific magnetic domain walls, providing the missing link between wave emission and wall dynamics near magnetic singularities. This work opens new possibilities in magnonics, offering a nanoscopic view of spin dynamics via transmission electron microscopy and enabling controlled excitation via radio-frequency fields for exploring non-equilibrium states in magnetic and multiferroic systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Dynamic signatures of spin-lattice coupling in the layered ferrimagnet Mn 3 Si 2 Te 6

Magnetic van der Waals (vdW) materials exhibit a profound interconnectedness between their various degrees of freedom, pointing to a wealth of potential applications in low-power and high-speed spintronic devices. Recently, light-matter interactions have been leveraged as robust, dynamic pathways to gain control over the properties of vdW magnets through the use of ultrafast pulses of light. Here, we utilize ultrafast photoexcitation to drive coherent lattice oscillations in the layered ferrimagnetic crystal Mn 3 Si 2 Te 6 , which significantly stiffen below the magnetic ordering temperature. We suggest that this is due to an exchange-mediated contraction of the lattice, stemming from strong magneto-structural coupling in this material. Furthermore, simulations of the transient incoherent response uncover the critical role of the spin-mediated electronic relaxation pathways. These results underscore the importance of spin-lattice coupling in vdW magnets and demonstrate a promising strategy for their dynamic optical control via their entangled degrees of freedom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

COLUMBUS─An Efficient and General Program Package for Ground and Excited State Computations Including Spin–Orbit Couplings and Dynamics

The COLUMBUS program system provides the tools for performing high-level multireference (MR) computations, including the multireference configuration interaction (MRCI) method and its multireference averaged quadratic coupled cluster (MR-AQCC) extension, allowing computations on a wide range of fascinating atomic and molecular systems, including the treatment of open-shells and complicated excited state phenomena. The inclusion of spin−orbit coupling (SOC) directly within the MRCI step enables the description of systems containing heavy elements, such as lanthanides and actinides, whose properties are strongly influenced by SOC. Analytic energy gradients and nonadiabatic couplings at the correlated MRCI level provide the foundation for a variety of dynamics studies, giving insight into ultrafast photochemistry. New and ongoing method developments in COLUMBUS include the computation of spin densities, improved descriptions of ionic states, enhancements to the AQCC method, and the porting of COLUMBUS to graphical processing units (GPUs). New external interfaces enable an enhanced description of electronic resonances and molecules in strong laser fields. This work highlights these new developments while providing a detailed account of the diverse applications of COLUMBUS in recent years.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗