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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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482 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Opposite current-induced spin polarizations in bulk-metallic Bi 2 Se 3 and bulk-insulating Bi 2 Te 2 Se topological insulator thin flakes

One of the most fundamental and exotic properties of three-dimensional (3D) topological insulators (TIs) is spin-momentum locking (SML) of their topological surface states (TSSs), promising for potential applications in future spintronics. However, other possible conduction channels, such as a trivial two-dimensional electron gas (2DEG) with strong Rashba-type spin-orbit interaction (SOI) and bulk-conducting states that may possess a spin Hall effect (SHE), can coexist in 3D TIs, making determining the origin of the current-induced spin polarization (CISP) difficult. Here, we directly compared the CISP between bulk-insulating Bi 2 Te 2 Se (BTS221) and bulk-metallic Bi2Se3 thin flakes using spin potentiometry. In the bulk-insulating BTS221, the observed CISP has a sign consistent with the expected helicity of the SML of the TSS, but an opposite sign to its calculated bulk spin Hall conductivity. However, compared to BTS221, an opposite CISP is observed in the bulk-metallic Bi2Se3, consistent with both the expectations of its Rashba-Edelstein effect of the band-bending induced 2DEG and bulk intrinsic spin Hall Effect (SHE). If one assumes a representative occupation of the Rashba band of 3×10 13 cm –2 in Bi 2 Se 3 with a relevant relaxation time of 100 fs, the contribution to the CISP could be more dominated by the bulk intrinsic SHE. Our results provide an electrical way to distinguish the TSS from other possible conducting channels in spin transport measurements on 3D TIs, and open ways for the potential applications in charge-spin conversion devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Enhancement of microwave to optical spin-based quantum transduction via a magnon mode

We propose a method for converting single microwave photons to single optical sideband photons based on spinful impurities in magnetic materials. This hybrid system is advantageous over previous proposals because (i) the implementation allows much higher transduction rates (10 3 times faster at the same optical pump Rabi frequency) than state-of-the-art devices, (ii) high-efficiency transduction is found to happen in a significantly larger space of device parameters (in particular, over 1 GHz microwave detuning), and (iii) it does not require mode volume matching between optical and microwave resonators. We identify the needed magnetic interactions as well as potential materials systems to enable this speed up using erbium dopants for telecom compatibility. This is an important step towards realizing high-fidelity entangling operations between remote qubits and will provide additional control of the transduction through perturbation of the magnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Low-Field Regime of Magnon Transport in PLD-Grown YIG Films

The diffusive propagation of magnons in the archetypal magnetic insulator yttrium iron garnet (YIG) is being actively explored for low-power and low-loss data communication. However, operation under external magnetic fields reduces the magnon diffusion length and attenuates the voltage amplitude at measurement terminals of magnonic devices. Here, we explore the low-field and field-free regime of diffusive magnon transport in YIG films, demonstrating that the field-induced suppression of magnon diffusion length can be fully inhibited only at the zero-field limit. Even a modest field of 10 mT attenuates the nonlocal spin voltage by ~20% in an ~1 μm long transport channel. We further identify the often overlooked in-plane uniaxial magnetic anisotropy as the dominant factor governing magnon transport in the low-field regime. Using Stoner-Wohlfarth macrospin simulations, we quantify the anisotropy parameters and reveal a 10-fold enhancement at low temperatures, a key finding for field-free operation of magnonic devices under cryogenic conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Predicting Phonon-Induced Spin Decoherence from First Principles: Colossal Spin Renormalization in Condensed Matter

Developing a microscopic understanding of spin decoherence is essential to advancing quantum technologies. Electron spin decoherence due to atomic vibrations (phonons) plays a special role as it sets an intrinsic limit to the performance of spin-based quantum devices. Two main sources of phonon-induced spin decoherence—the Elliott-Yafet and Dyakonov-Perel mechanisms—have distinct physical origins and theoretical treatments. Here, we show calculations that unify their modeling and enable accurate predictions of spin relaxation and precession in semiconductors. We compute the phonon-dressed vertex of the spin-spin correlation function with a treatment analogous to the calculation of the anomalous electron magnetic moment in QED. We find that the vertex correction provides a giant renormalization of the electron spin dynamics in solids, greater by many orders of magnitude than the corresponding correction from photons in vacuum. Finally, our Letter demonstrates a general approach for quantitative analysis of spin decoherence in materials, advancing the quest for spin-based quantum technologies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Magnetic Solitons and Thickness‐Dependent Magnetization Reversal in Interconnected Helical Nanowire Arrays

By expanding magnetic nanostructures into the third dimension, it is possible to introduce new interactions and realize new forms of magnetic textures and emergent phenomena. Consequently, this unlocks new opportunities for applications in data storage, unconventional computing and sensing by utilizing 3D devices with enhanced functionalities. Connected magnetic nanowires offer a unique platform for applications such as neuromorphic computing due to their tunability and the presence of multiple transport pathways. However to realize this promise, it is necessary to further our understanding of how to locally control the magnetization in 3D, nanowire-based geometries. In this work we show the formation of magnetic domain walls, vortices, anti-vortices, and linked vortex-anti-vortex pairs in interconnected helical nanowire arrays. We show how wire diameter and 3D geometric design can control the states that form and reveal the magnetization reversal mechanism. Hence, we demonstrate this to be a highly tunable system, where the magnetization can be readily reconfigured by an external magnetic field.

3D Nanomagnetism↗
DOE OSTI2023

Long-lived electronic spin qubits in single-walled carbon nanotubes

Abstract Electron spins in solid-state systems offer the promise of spin-based information processing devices. Single-walled carbon nanotubes (SWCNTs), an all-carbon one-dimensional material whose spin-free environment and weak spin-orbit coupling promise long spin coherence times, offer a diverse degree of freedom for extended range of functionality not available to bulk systems. A key requirement limiting spin qubit implementation in SWCNTs is disciplined confinement of isolated spins. Here, we report the creation of highly confined electron spins in SWCNTs via a bottom-up approach. The record long coherence time of 8.2 µs and spin-lattice relaxation time of 13 ms of these electronic spin qubits allow demonstration of quantum control operation manifested as Rabi oscillation. Investigation of the decoherence mechanism reveals an intrinsic coherence time of tens of milliseconds. These findings evident that combining molecular approaches with inorganic crystalline systems provides a powerful route for reproducible and scalable quantum materials suitable for qubit applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Space-Charge-Limited van der Waals Spin Transistor

Integrating semiconducting and magnetic materials could combine transistorlike operation with nonvolatility and enable architectures such as logic in memory. Here, in this work, we employ correlated electrical transport and scanning nitrogen-vacancy center magnetic imaging to elucidate a spin transistor concept that amalgamates vertical and lateral hopping transport inside a 2D antiferromagnetic semiconductor, mechanistically distinct from vertical tunneling devices. Our device, based on a monolayer-bilayer junction in CrSBr, displays giant, gate-tunable magnetoresistance driven by the dual action of electrostatic doping on space-charge-limited lateral conduction and interlayer exchange coupling. Moreover, we visualize a field-trainable, layer-sharing effect that selects between coherent or domain-wall reversal at the spin-flip transition, enabling multilevel, memristive conductance states. Our layer-dependent space charge mechanism for convergent electrical and magnetic control opens opportunities to address limitations in contemporary computing.

2-dimensional systems↗
DOE OSTI2025

Tunable high Néel temperature and large anomalous Hall response in antiferromagnetic Weyl semimetal Mn 3 Sn 1− x Ga x thin films

Antiferromagnetic Weyl semimetals based on Mn 3 X(X = Ge, Sn, Ga) kagome compounds exhibit the same ferromagnetic-like responses, including anomalous Hall, Nernst, and magneto-optical effects, as recently discussed for altermagnets. Driven by the Berry curvature due to Weyl fermions, these materials show a disproportionately large magnitude of electromagnetic effects even in the absence of large magnetization. For applications it is crucial to realize these responses in a wide range of temperatures both below and above 300 K. While stoichiometric Mn 3 X materials do not offer optimal performance, we show that Mn 3 Sn 1−x Ga x sputtered films with a variable composition offers a tunable Néel temperature, T N ≈ 425 ± 6–500 ± 15 K, which is crucial for device applications, together with a large tunable anomalous Hall effect. Our thin film growth method enables continuous and precise control over the film composition between x = 0 and x = 1. Through a detailed magnetization and Hall transport, we establish the magnetic phase diagram for the hexagonal Mn 3 Sn 1−x Ga x . Our results reveal an enhanced T N and antichiral magnetic phase in Ga-doped Mn 3 Sn and an enhanced anomalous Hall magnitude in Sn-doped Mn 3 Ga compared to their stoichiometric undoped forms. Our work demonstrates a route to optimize the technologically relevant antiferromagnets for various applications.

Magnetic properties and materials↗
DOE OSTI2024

Reconfigurable spin current transmission and magnon–magnon coupling in hybrid ferrimagnetic insulators

Coherent spin waves possess immense potential in wave-based information computation, storage, and transmission with high fidelity and ultra-low energy consumption. However, despite their seminal importance for magnonic devices, there is a paucity of both structural prototypes and theoretical frameworks that regulate the spin current transmission and magnon hybridization mediated by coherent spin waves. Here, we demonstrate reconfigurable coherent spin current transmission, as well as magnon–magnon coupling, in a hybrid ferrimagnetic heterostructure comprising epitaxial Gd 3 Fe 5 O 12 and Y 3 Fe 5 O 12 insulators. By adjusting the compensated moment in Gd 3 Fe 5 O 12 , magnon–magnon coupling was achieved and engineered with pronounced anticrossings between two Kittel modes, accompanied by divergent dissipative coupling approaching the magnetic compensation temperature of Gd 3 Fe 5 O 12 (T M,GdIG ), which were modeled by coherent spin pumping. Remarkably, we further identified, both experimentally and theoretically, a drastic variation in the coherent spin wave-mediated spin current across T M,GdIG , which manifested as a strong dependence on the relative alignment of magnetic moments. Our findings provide significant fundamental insight into the reconfiguration of coherent spin waves and offer a new route towards constructing artificial magnonic architectures.

42 ENGINEERING↗
DOE OSTI2026

Strain-stabilized interfacial polarization tunes work function over 1 eV in RuO 2 /TiO 2 heterostructures

Interfacial polarization – charge accumulation at the heterointerface – is a well-established tool in semiconductors, but its influence in metals remains unexplored. Here, we demonstrate that interfacial polarization can robustly modulate surface work function in metallic rutile RuO 2 layers in epitaxial RuO 2 /TiO 2 heterostructures grown by hybrid molecular beam epitaxy. Using multislice electron ptychography, we directly visualize polar displacements of transition metal ions relative to oxygen octahedra near the interface, despite the conductive nature of RuO 2 . This interfacial polarization enables over 1 eV modulation of the RuO 2 work function, controlled by small thickness variations (2-3 nm), as measured by Kelvin probe force microscopy, with a critical thickness of ~4 nm – corresponding to the transition from fully-strained to relaxed film. These results establish interfacial polarization as a powerful route to control electronic properties in metals and have implications for designing tunable electronic, catalytic, and quantum devices through interfacial control in polar metallic systems.

Electronic properties and materials↗
DOE OSTI2020

Photoinduced charge transfer in transition metal dichalcogenide heterojunctions – towards next generation energy technologies

Increasing interest in using two-dimensional transition metal dichalcogenides (2D TMDCs) in optical energy conversion technologies creates a demand for improving the yields and lifetimes of photogenerated charge carriers. Despite inherently fast photocarrier decay in neat 2D TMDCs, the unique photophysics in these quantum-confined systems motivates continued effort to control the evolution of photoexcited states and create functional devices. Here, an intriguing strategy to accomplish this goal is to employ TMDCs in heterojunctions with appropriate semiconductors, where energy level offsets drive photoinduced charge transfer (PCT) across material interfaces. PCT in TMDC-based systems can be optimized for many different applications, such as driving free carriers to photocatalytic sites for redox reactions like water splitting, extracting charge to perform work in photovoltaics or photodetectors, and manipulating the spin and momentum valley electronic degrees of freedom for quantum computing systems. Here, we review recent strides in optimizing PCT for such applications through greater fundamental understanding of the photophysics that occurs at TMDC/semiconductor interfaces. After giving an overview of isolated TMDC properties, synthetic methods, and the basics of PCT, we discuss TMDCs in heterojunctions with several classes of materials, including other TMDCs, small molecule semiconductors, polymers, single-walled carbon nanotubes, quantum dots, perovskites, and electrolytes. In addition to highlighting the unique benefits of each materials category, we also identify parallels across common themes, such as the roles of charge-transfer states, spin, electronic coupling, delocalization, interfacial atomic morphology, and the precise design of energy landscapes to direct charge and energy motion. We hope to capture a broad range of the valuable work in this fast-paced field to inspire new research directions for employing PCT in targeted TMDC-based systems.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Nuclear spin engineering for quantum information science

Semiconductors are the backbone of modern technology, garnering decades of investment in high-quality materials and devices. Electron spin systems in semiconductors, including atomic defects and quantum dots, have been demonstrated in the last two decades to host quantum coherent spin qubits, often with coherent spin–photon interfaces and proximal nuclear spins. These systems are at the center of developing quantum technology. However, new material challenges arise when considering the isotopic composition of host and qubit systems. The isotopic composition governs the nature and concentration of nuclear spins, which naturally occur in leading host materials. These spins generate magnetic noise—detrimental to qubit coherence—but also show promise as local quantum memories and processors, necessitating careful engineering dependent on the targeted application. Reviewing recent experimental and theoretical progress toward understanding local nuclear spin environments in semiconductors, we show this aspect of material engineering as critical to quantum information technology.

Defects↗
DOE OSTI2020

Chemical substitution induced half-metallicity in CrMnSb (1– x ) P x

Half-metallic Heusler alloys have been intensively studied in recent years due to their potential applications in spin-based devices, e.g., in magnetic tunnel junctions. Yet, their properties may be very sensitive to the choice of the substrates, i.e., to the epitaxial strain and interface properties. Here, we report the results of our computational work on the half-Heusler compound CrMnSb (1–x) P x . In particular, we demonstrate that the parent compound CrMnSb is close to a half-metallic material at the optimized lattice parameter, with the onset of the half-metallic bandgap a few meV above the Fermi energy. Moreover, although it undergoes a half-metallic transition under a uniform compression of ~1.5%, such a transition is absent under epitaxial strain. At the same time, we show that a half-metallic transition could be induced by a chemical substitution of Sb with P, which results in a volume reduction of the unit cell. In particular, 50% substitution of Sb with P leads to a robust half-metallicity in CrMnSb (1–x) P x , with 100% spin polarization being retained at a large range of epitaxial strain. Furthermore, our results indicate that CrMnSb0.5P0.5 could be grown on different types of substrates, e.g., GaAs, without its electronic properties being detrimentally affected by biaxial strain. In addition, CrMnSb 0.5 P 0.5 exhibits a fully compensated ferrimagnetic alignment, which could be potentially useful in applications where stray magnetic fields are undesirable.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO 2 /Fe Bilayer Heterostructures

Initially identified as a promising altermagnetic (AM) candidate, rutile RuO 2 has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk nonmagnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patterned RuO 2 Hall bars and film heterostructures display magnetotransport signatures of magnetic ordering. Among the characteristics routinely cited as evidence for AM is the observation of exchange bias (EB) in an intimately contacted Fe-based ferromagnetic (FM) layer, which can arise due to interfacial coupling with a compensated antiferromagnet. Here, within this work, the origins of this EB coupling in Ru-capped RuO 2 /Fe bilayers are investigated using polarized neutron diffraction, polarized neutron reflectometry, cross-sectional transmission electron microscopy, and super conducting quantum interference device measurements. These experiments reveal that the EB behavior is driven by the formation of an iron oxide interlayer containing Fe 3 O 4 that undergoes a magnetic transition and pins interfacial moments within Fe at low temperature. These findings are confirmed by comparable measurements of Ni-based heterostructures, which do not display EB coupling, as well as magnetometry of additional Fe/Ru bilayers that display oxide-driven EB coupling despite the absence of the epitaxial RuO 2 layer. While these results do not directly refute the possibility of AM ordering in RuO 2 thin films, they reveal that EB, and related magnetotransport phenomena, cannot alone be considered evidence of this characteristic in the rutile structure due to interfacial chemical disorder.

RuO2↗