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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Non‐Fermi‐Liquid Behavior of Superconducting SnH 4

Abstract The chemical interaction of Sn with H 2 by X‐ray diffraction methods at pressures of 180–210 GPa is studied. A previously unknown tetrahydride SnH 4 with a cubic structure ( fcc ) exhibiting superconducting properties below T C = 72 K is obtained; the formation of a high molecular C 2/ m ‐SnH 14 superhydride and several lower hydrides, fcc SnH 2 , and C 2‐Sn 12 H 18 , is also detected. The temperature dependence of critical current density J C (T) in SnH 4 yields the superconducting gap 2Δ(0) = 21.6 meV at 180 GPa. SnH 4 has unusual behavior in strong magnetic fields: B,T ‐linear dependences of magnetoresistance and the upper critical magnetic field B C2 (T) ∝ ( T C – T ). The latter contradicts the Wertheimer–Helfand–Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH 4 in non‐superconducting state exhibits a deviation from what is expected for phonon‐mediated scattering described by the Bloch‐Grüneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Angular‐Momentum Transfer Mediated by a Vibronic‐Bound‐State

Abstract The notion that phonons can carry pseudo‐angular momentum has many major consequences, including topologically protected phonon chirality, Berry curvature of phonon band structure, and the phonon Hall effect. When a phonon is resonantly coupled to an orbital state split by its crystal field environment, a so‐called vibronic bound state forms. Here, a vibronic bound state is observed in NaYbSe 2 , a quantum spin liquid candidate. In addition, field and polarization dependent Raman microscopy is used to probe an angular momentum transfer of Δ J z = ±ℏ between phonons and the crystalline electric field mediated by the vibronic bound stat. This angular momentum transfer between electronic and lattice subsystems provides new pathways for selective optical addressability of phononic angular momentum via electronic ancillary states.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Transition Metal Dichalcogenides: Making Atomic‐Level Magnetism Tunable with Light at Room Temperature

Abstract The capacity to manipulate magnetization in 2D dilute magnetic semiconductors (2D‐DMSs) using light, specifically in magnetically doped transition metal dichalcogenide (TMD) monolayers ( M ‐doped TX 2 , where M = V, Fe, and Cr; T = W, Mo; X = S, Se, and Te), may lead to innovative applications in spintronics, spin‐caloritronics, valleytronics, and quantum computation. This Perspective paper explores the mediation of magnetization by light under ambient conditions in 2D‐TMD DMSs and heterostructures. By combining magneto‐LC resonance (MLCR) experiments with density functional theory (DFT) calculations, we show that the magnetization can be enhanced using light in V‐doped TMD monolayers (e.g., V‐WS 2 , V‐WSe 2 ). This phenomenon is attributed to excess holes in the conduction and valence bands, and carriers trapped in magnetic doping states, mediating the magnetization of the semiconducting layer. In 2D‐TMD heterostructures (VSe 2 /WS 2 , VSe 2 /MoS 2 ), the significance of proximity, charge‐transfer, and confinement effects in amplifying light‐mediated magnetism is demonstrated. We attributed this to photon absorption at the TMD layer that generates electron–hole pairs mediating the magnetization of the heterostructure. These findings will encourage further research in the field of 2D magnetism and establish a novel design of 2D‐TMDs and heterostructures with optically tunable magnetic functionalities, paving the way for next‐generation magneto‐optic nanodevices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A Quenched Disorder in the Quantum-Critical Superconductor CeCoIn 5

Emergent inhomogeneous electronic phases in metallic quantum systems are crucial for understanding high- T c superconductivity and other novel quantum states. In particular, spin droplets introduced by nonmagnetic dopants in quantum-critical superconductors (QCSs) can lead to a novel magnetic state in superconducting phases. However, the role of disorders caused by nonmagnetic dopants in quantum-critical regimes and their precise relation with superconductivity remain unclear. Here, the systematic evolution of a strong correlation between superconductive intertwined electronic phases and antiferromagnetism in Cd-doped CeCoIn 5 is presented by measuring current–voltage characteristics under an external pressure. In the low-pressure coexisting regime where antiferromagnetic (AFM) and superconducting (SC) orders coexist, the critical current ( I c ) is gradually suppressed by the increasing magnetic field, as in conventional type-II superconductors. At pressures higher than the critical pressure where the AFM order disappears, I c remarkably shows a sudden spike near the irreversible magnetic field. In addition, at high pressures far from the critical pressure point, the peak effect is not suppressed, but remains robust over the whole superconducting region. These results indicate that magnetic islands are protected around dopant sites despite being suppressed by the increasingly correlated effects under pressure, providing a new perspective on the role of quenched disorders in QCSs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Coupling Between Electrons and Charge Density Wave Fluctuation and its Possible Role in Superconductivity

In most charge density wave (CDW) systems of different material classes, ranging from traditional correlated systems in low-dimension to recent topological systems with Kagome lattice, superconductivity emerges when the system is driven toward the quantum critical point (QCP) of CDW via external parameters of doping and pressure. Despite this rather universal trend, the essential hinge between CDW and superconductivity has not been established yet. Here, the evidence of coupling between electron and CDW fluctuation is reported, based on a temperature- and intercalation-dependent kink in the angle-resolved photoemission spectra of 2H-Pd x TaSe 2 . Kinks are observed only when the system is in the CDW phase, regardless of whether a long- or short-range order is established. Notably, the coupling strength is enhanced upon long-range CDW suppression, albeit the coupling energy scale is reduced. Interestingly, the estimation of the superconducting critical temperature by incorporating the observed coupling characteristics into McMillan's equation yields results closely resembling the known values of the superconducting dome. The results thus highlight a compelling possibility that this new coupling mediates Cooper pairs, which provides new insights into the competing relationship not only for CDW but also for other competing orders.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Direct Observation of Vortex Liquid Droplets in the Iron Pnictide Superconductor CaKFe 4 As 4 at 0.5T c

Type-II superconductors under magnetic fields remain in a quantum-coherent, non-dissipative state as long as vortices are pinned. Dissipation emerges when vortices depin, a process often driven by thermal fluctuations and commonly associated with a melting transition from a vortex solid to a vortex liquid. Macroscopic experiments almost always observe this transition close to the superconducting critical temperature 𝑇 𝑐 . However, how the vortex solid responds to thermal fluctuations at the scale of individual vortices, far below the melting transition, remains largely unexplored. Here, we use scanning tunneling microscopy (STM) to directly visualize vortices in the iron-based superconductor CaKFe 4 ⁢As 4 (𝑇 𝑐 ≈35 K ). We observe the formation of vortex liquid droplets—spatially localized regions where vortices exhibit strong thermal fluctuations—at temperatures as low as 0.5 𝑇 𝑐 . These results demonstrate that the onset of dissipation at the local scale occurs at temperatures significantly below 𝑇𝑐 in type-II superconductors, revealing a previously unrecognized regime of vortex dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

2D Mg-Cu Intermetallic Compounds with Nontrivial Band Topology and Dirac Nodal Lines

Synthesis of vertical heterostructures that include atomically thin layers of materials with topologically nontrivial energy bands is desirable for exploring exotic quantum states. In this study, the authors report on atomic-layer-by-layer deposition of magnesium on copper(111) surface by molecular beam epitaxy, monitored in situ by low-energy electron microscopy and diffraction, and modeled by ab initio theory. It is found that a 2D MgCu 2 intermetallic compound forms during initial Mg deposition and persists till a full monolayer of Mg is formed. Deposition of additional Mg triggers a phase transition from the commensurate MgCu 2 to an incommensurate Mg 2 Cu layer and enables growth of the second layer of Mg. Ab initio calculations indicate non-trivial topology of the electron bands in the interfacial Mg 2 Cu layer and the existence of Dirac nodal lines near the Fermi level. The new 2D Mg 2 Cu material emerges as a promising platform to study new topological states of matter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Spontaneous Symmetry–Breaking of Nonequilibrium Steady–States Caused by Nonlinear Electrical Transport

Negative differential resistance (NDR) in certain materials has been attributed to spontaneous emergence of symmetry-breaking electrical current density localization from a previously homogeneous distribution, which is postulated to occur due to the nonequilibrium thermodynamic force of minimization of entropy production. However, this phenomenon has not been quantitatively predicted based on intrinsic material properties and an applied electrical stimulus. Herein an instability criterion is derived for localization of current density and temperature from a thermal fluctuation in a parallel conductor model of a thin film that is subject to Newton's law of cooling. The conditions for steady–state electro-thermal localization is predicted, verifying a decrease in entropy production upon localization. Electro-thermal localization accompanied by a decrease of entropy production is confirmed in a multiphysics simulation of current flow in a thin film. The instability criterion predicts conditions for spontaneous current density localization, relating symmetry breaking fundamentally to dynamical instability via Local Activity theory.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Understanding and Tuning Magnetism in Layered Ising‐Type Antiferromagnet FePSe 3 for Potential 2D Magnet

Abstract Recent developments in 2D magnetic materials have motivated the search for new van der Waals magnetic materials, especially Ising‐type magnets with strong magnetic anisotropy. Fe‐based M P X 3 ( M = transition metal, X = chalcogen) compounds such as FePS 3 and FePSe 3 both exhibit an Ising‐type magnetic order, but FePSe 3 receives much less attention compared to FePS 3 . This work focuses on establishing the strategy to engineer magnetic anisotropy and exchange interactions in this less‐explored compound. Through chalcogen and metal substitutions, the magnetic anisotropy is found to be immune against S substitution for Se whereas tunable only with heavy Mn substitution for Fe. In particular, Mn substitution leads to a continuous rotation of magnetic moments from the out‐of‐plane direction toward the in‐plane. Furthermore, the magnetic ordering temperature displays non‐monotonic doping dependence for both chalcogen and metal substitutions but due to different mechanisms. These findings provide deeper insight into the Ising‐type magnetism in this important van der Waals material, shedding light on the study of other Ising‐type magnetic systems as well as discovering novel 2D magnets for potential applications in spintronics.

2D magnet↗
DOE OSTI2024

Evolution of Dissipative Regimes in Atomically Thin Bi 2 Sr 2 CaCu 2 O 8 + x Superconductor

Thermoelectric transport is widely used to study Abrikosov vortex dynamics in unconventional superconductors. However, only a few thermoelectric studies have been conducted near the dimensional crossover that occurs when the vortex-vortex interaction length scale becomes comparable to the sample size. Here, the effects of finite size on the dissipation mechanisms of the Nernst effect in the optimally doped Bi 2 Sr 2 CaCu 2 O 8 + x high-temperature superconductor are reported, down to the atomic length limit. To access this regime, a new generation of thermoelectric chips based on silicon nitride microprinted circuit boards is developed. These chips ensure optimized signals while preventing sample deterioration. The results demonstrate that lateral confinement at the nanoscale can effectively reduce vortex dissipation. Investigating vortex dissipation at the micro- and nano-scale is essential for creating stable, miniaturized superconducting circuits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Direct‐Write Printed Contacts to Layered and 2D Materials

Advancements in fabrication methods have shaped new computing device technologies. Among these methods, depositing electrical contacts to the channel material is fundamental to device characterization. Novel layered and 2D materials are promising for next-generation computing electronic channel materials. Direct-write printing of conductive inks is introduced as a surprisingly effective, significantly faster, and cleaner method to contact different classes of layered materials, including graphene (semi-metal), MoS 2 (semiconductor), Bi-2212 (superconductor), and Fe 5 GeTe 2 (metallic ferromagnet). Based on the electrical response, the quality of the printed contacts is comparable to what is achievable with resist-based lithography techniques. These devices are tested by sweeping gate voltage, temperature, and magnetic field to show that the materials remain pristine post-processing. This work demonstrates that direct-write printing is an agile method for prototyping and characterizing the electrical properties of novel layered materials.

2D materials↗
DOE OSTI2020

Direct Observation of Alternating Octahedral and Prismatic Sodium Layers in O3-Type Transition Metal Oxides

The oxygen stacking of O3-type layered sodium transition metal oxides (O3-NaTMO 2 ) changes dynamically upon topotactic Na extraction and reinsertion. While the phase transition from octahedral to prismatic Na coordination that occurs at intermediate desodiation by transition metal slab gliding is well understood, the structural evolution at high desodiation, crucial to achieve high reversible capacity, remains mostly uncharted. In this work, the phase transitions of O3-type layered NaTMO 2 at high voltage are investigated by combining experimental and computational approaches. An OP2-type phase that consists of alternating octahedral and prismatic Na layers is directly observed by in situ X-ray diffraction and high-resolution scanning transmission electron microscopy. The origin of this peculiar phase is explained by atomic interactions involving Jahn–Teller active Fe 4+ and distortion tolerant Ti 4+ that stabilize the local Na environment. Finally, the path-dependent desodiation and resodiation pathways are also rationalized in this material through the different kinetics of the prismatic and octahedral layers, presenting a comprehensive picture about the structural stability of the layered materials upon Na intercalation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Hydrostatic and Uniaxial Pressure Tuning of Iron-Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely-observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to asnematic transition. Nematicity is therefore a prominent feature of these materials, which signals the importance of the coupling of electronic and lattice properties. Correspondingly, these systems are particularly susceptible to tuning via pressure (hydrostatic, uniaxial, or some combination). We review efforts to probe the phase diagrams of pressure-tuned iron-based superconductors, with a strong focus on our own recent insights into the phase diagrams of several members of this mate-rial class under hydrostatic pressure. These studies on FeSe, Ba(Fe 1-x Co x ) 2 As 2 , Ca(Fe 1-x Co x ) 2 As 2 and CaK(Fe 1-x Ni x ) 4 As 4 were, to a significant extent, made possible by advances of what measurements can be adapted to the use under differing pressure environments. We point out the potential impact of these tools for the study of the wider class of strongly correlated electron systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Vibrational Properties of Pristine and Lithium-Intercalated Black Phosphorous under High-Pressure

Structural evolution of Li-intercalated and pristine black phosphorous (BP) under high-pressure (up to ≈8 GPa) is studied using in situ Raman spectroscopy. Even though both materials show a monotonic blueshift of the out-of-plane vibrational mode (A 1 g ) with pressure, Li-intercalated BP do not show a blueshift until a threshold pressure (2.4 GPa) is reached to compensate the structural expansion caused by intercalation. However, the in-plane modes (B 2g and A 2 g) in each sample respond differently. In the mid-pressure region, they both show redshifts which in Li-intercalated BP is also followed by abrupt blueshifts. Such behavior indicates pressure-induced structural reorganizations inside the material. Computational modeling reveals the existence of a process of P-P bond breaking and reforming in the system due to the redistribution of intercalated Li atoms under pressure. This work shows the significance of combined effect of pressure and intercalation on structural changes in the search for new phases of BP and other two-dimensional (2D) materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Multimodal Imaging of Autofluorescent Sites Reveals Varied Chemical Speciation in SSZ-13 Crystals

Here, a multimodal imaging study of chabazite is used to show the distribution of and discriminate between different emissive deposits arising as a result of the detemplation process. 3D confocal imaging, fluorescence lifetime imaging, spectral imaging, and Raman mapping are used to show three different types of emissive behaviours each characterised by different spatial distributions, trends in lifetime, spectral signals, and Raman signatures. A notable difference is seen in the morphology of agglomerated surface deposits and larger subsurface deposits, which experience lifetime augmentation due to spatial confinement. The distribution of organic residue throughout the crystal volume is comparable to XRF mapping that shows Si enrichment on the outer edges and higher Al content through the centre, demonstrating that a fluorescence-based technique can also be used to indirectly comment on the compositional chemistry of the inorganic framework.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

A Boosted Critical Temperature of 166 K in Superconducting D 3 S Synthesized from Elemental Sulfur and Hydrogen

The discovery of superconductivity in H 3 S at 203 K marked an advance towards room-temperature superconductivity and demonstrated the potential of H-dominated compounds to possess a high critical temperature (T c ). There have been numerous reports of the H-S system over the last five years, but important questions remain unanswered. It is crucial to verify whether the Tc was determined correctly for samples prepared from compressed H 2 S, since they are inevitably contaminated with H-depleted byproducts. Here, we prepare stoichiometric H 3 S by direct in situ synthesis from elemental S and excess H 2 . The Im$_\bar{3}$ m phase of D 3 S samples exhibits a T c significantly higher than previously reported values (ca. 150 K), reaching a maximum T c of 166 K at 157 GPa. Furthermore, we confirm that the sharp decrease in T c below 150 GPa is accompanied by continuous rhombohedral structural distortions and demonstrate that the Cccm phase is nonmetallic, with molecular H 2 units in the crystal structure.

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

Giant Magnetostriction in Ferrimagnetic SmFe 5 As 3

Magnetostrictive materials are of interest not only from a fundamental perspective but also for their potential applications, spanning spintronics to energy harvesting. A new magnetostrictive material—SmFe 5 As 3 —reveals a complex interplay between magnetostriction, magnetic properties, and the crystal structure behavior. The ground state of SmFe 5 As 3 is ferrimagnetic, as evidenced by magnetic susceptibility data, band-structure calculations, and XANES measurements. At T m1 = 28 ± 4 K, part of the Fe sublattice reorients, transitioning into a ferromagnetic state. This is followed by an entrance into the paramagnetic state at T m2 = 76 ± 4 K. The effects observed in the magnetic measurements are accompanied by structural phase transitions. All three phases—below T m1 , between T m1 and T m2 , and above T m2 —are described by the same structural motif of the UCr 5 P 3 type (monoclinic space group P2 1 /m), differing only in the degree of deformation of the Fe–As framework. The new material exhibits giant magnetostriction of 2500 x 10 -6 . Dilatometry measurements on a SmFe 5 As 3 single crystal indicate strongly diverse behavior, exhibiting not only negative, but also zero, as well as positive thermo-elastic effects.

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

Surface Local Impurity Scattering as a Probe for Topological Kondo Insulators

Shortly after the discovery of topological band insulators, topological Kondo insulators (TKIs) is also theoretically predicted. The latter has ignited revival interest in the properties of Kondo insulators. Currently, the feasibility of topological nature in SmB 6 is intensively analyzed by several complementary probes. Here by starting with a minimal-orbital Anderson lattice model, the local electronic structure is explored in a Kondo insulator. It is showed that the two strong topological regimes sandwiching the weak topological regime give rise to a single Dirac cone, which is located near the center or corner of the surface Brillouin zone. It is further found that, when a single impurity is placed on the surface, low-energy resonance states are induced in the weak scattering limit for the strong TKI regimes and the resonance level moves monotonically across the hybridization gap with the strength of impurity scattering potential; while low energy states can only be induced in the unitary scattering limit for the weak TKI regime, where the resonance level moves universally toward the center of the hybridization gap. These impurity-induced low-energy quasiparticles will lead to characteristic signatures in scanning tunneling microscopy/spectroscopy, which has recently found success in probing into exotic properties in heavy fermion systems.

36 MATERIALS SCIENCE↗