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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Rapid retrieval of first-order spatiotemporal distortions for ultrashort laser pulses

High-intensity, ultrashort laser sources are a foundational pillar for High-Energy-Density (HED) physics, and as the repetition-rates of these systems increase, diagnostics must be developed to match their data collection speed. Characterization of any spatiotemporal distortions in the laser pulse is necessary in order to standardize results across facilities. Here, we have previously developed a laser diagnostic called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram, or STRIPED FISH, to measure the full spatiotemporal laser electric field on a single shot. In order to provide rapid feedback, we here adapt the STRIPED FISH retrieval algorithm, which typically has computation times of up to 30 minutes due to the high spatial resolution of the device and its retrieval of the complete four-dimensional pulse field, to distill the key electric field quantities into a handful of scalars for rapid assessment of the pulse's first order distortions. Here, our new, rapid non-iterative retrieval algorithm is validated with simulated and experimental data, and it provides, within seconds, the same first-order information as given by the full analysis. This algorithm is suitable for on-shot assessment of spatiotemporal distortions and can be adapted to assess high repetition-rate laser quality in HED experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Gapped commensurate antiferromagnetic response in a strongly underdoped model cuprate superconductor

It is a distinct possibility that spin fluctuations are the pairing interactions in numerous unconventional superconductors. In the high-transition-temperature (high-T c ) cuprates, superconductivity emerges upon doping antiferromagnetic Mott insulators, and spin fluctuations might furthermore drive unusual pseudogap phenomena. Here we use magnetic neutron scattering to study the highly underdoped cuprate HgBa 2 CuO 4+δ (hole concentration p ≈ 0.064). In contrast to prior results for other underdoped cuprates, we find no evidence of incommensurate magnetic order associated with spin-density-wave or stripe correlations. Instead, the antiferromagnetic response in both the superconducting and pseudogap states is gapped below Δ AF ≈ 6 meV, commensurate over a wide energy range, and disperses above about 55 meV. Given the pristine nature of HgBa 2 CuO 4+δ , which exhibits high structural symmetry and minimal point disorder effects, this behavior likely signifies the unmasked response of the underlying CuO 2 planes near the Mott-insulating state. These results serve as a benchmark for a refined theoretical understanding of the cuprates.

Materials science↗
DOE OSTI2022

Examining AGN UV/Optical Variability beyond the Simple Damped Random Walk

We present damped harmonic oscillator (DHO) light-curve modeling for a sample of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey Stripe 82 region. DHO is a second-order continuous-time autoregressive moving-average process, which can be fully described using four independent parameters: a natural oscillation frequency (ω 0 ), a damping ratio (ξ), a characteristic perturbation timescale (τ perturb ), and an amplitude for the perturbing white noise (σ ϵ ). The asymptotic variability amplitude of a DHO process is quantified by σ DHO —a function of ω 0 , ξ, τ perturb , and σ ϵ . We find that both τ perturb and σ ϵ follow different dependencies with rest-frame wavelength (λ RF ) on either side of 2500 Å, whereas σ DHO follows a single power-law relation with λ RF . After correcting for wavelength dependence, σ DHO exhibits anticorrelations with both the Eddington ratio and the black hole mass, while τ perturb —with a typical value of days in the rest frame—shows an anticorrelation with the bolometric luminosity. Modeling active galactic nuclei (AGN) variability as a DHO offers more insight into the workings of accretion disks close to the supermassive black holes at the center of AGN. The newly discovered short-term variability (characterized by τ perturb and σ ϵ ) and its correlation with bolometric luminosity pave the way for new algorithms that will derive fundamental properties (e.g., Eddington ratio) of AGN using photometric data alone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Peak effect and dynamics of stripe- and pattern-forming systems on a periodic one-dimensional substrate

Here we examine the ordering, pinning, and dynamics of two-dimensional pattern-forming systems interacting with a periodic one-dimensional substrate. In the absence of the substrate, particles with competing long-range repulsion and short-range attraction form anisotropic crystal, stripe, and bubble states. When the system is tuned across the stripe transition in the presence of a substrate, we find that there is a peak effect in the critical depinning force when the stripes align and become commensurate with the substrate. Under an applied drive, the anisotropic crystal and stripe states can exhibit soliton depinning and plastic flow. When the stripes depin plastically, they dynamically reorder into a moving stripe state that is perpendicular to the substrate trough direction. We also find that when the substrate spacing is smaller than the widths of the bubbles or stripes, the system forms pinned stripe states that are perpendicular to the substrate trough direction. The system exhibits multiple reentrant pinning effects as a function of increasing attraction, with the anisotropic crystal and large bubble states experiencing weak pinning but the stripe and smaller bubble states showing stronger pinning. We map out the different dynamic phases as a function of filling, the strength of the attractive interaction term, the substrate strength, and the drive, and demonstrate that the different phases produce identifiable features in the transport curves and particle orderings.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Fluctuating intertwined stripes in the strange metal regime of the Hubbard model

Strongly correlated electron systems host a variety of poorly understood correlations in their high-temperature normal state. Unlike ordered phases defined by order parameters, regions of the normal state are often defined through unconventional properties such as strange metallic transport or spectroscopic pseudogaps. Characterizing the microscopic correlations in the normal state is necessary to elucidate mechanisms that lead to these properties and their connection to ground-state orders. Here, in this paper, we establish the presence of intertwined charge and spin stripes in the strange metal normal state of the Hubbard model using determinant quantum Monte Carlo calculations. The charge and spin density waves constituting the stripes are fluctuating and short ranged; yet they obey a mutual commensurability relation and remain microscopically interlocked, as evidenced through measurements of three-point spin-spin-hole correlation functions. Our findings demonstrate the ability of many-body numerical simulations to unravel the microscopic correlations that define quantum states of matter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Random strain induced correlations in materials with intertwined nematic and magnetic orders

Electronic nematicity is rarely observed as an isolated instability of a correlated electron system. Instead, in iron pnictides and in certain cuprates and heavy-fermion materials, nematicity is intertwined with an underlying spin-stripe or charge-stripe state. As a result, random strain, ubiquitous in any real crystal, creates both random-field disorder for the nematic degrees of freedom and random-bond disorder for the spin or charge ones. Here, we put forward an Ashkin-Teller model with random Baxter fields to capture the dual role of random strain in nematic systems for which nematicity is a composite order arising from a stripe state. Using Monte Carlo to simulate this random Baxter-field model, we find not only the expected break-up of the system into nematic domains, but also the emergence of nontrivial disorder-promoted magnetic correlations. Such correlations enhance and tie up the fluctuations associated with the two degenerate magnetic stripe states from which nematicity arises, leaving characteristic signatures in the spatial profile of the magnetic domains, in the configurational space of the spin variables, and in the magnetic noise spectrum. We discuss possible experimental manifestations of these effects in iron-pnictide superconductors. Furthermore, our work establishes the random Baxter-field model as a more complete alternative to the random-field Ising model to describe complex electronic nematic phenomena in the presence of disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Atomic-scale visualization of a cascade of magnetic orders in the layered antiferromagnet GdTe3

Abstract GdTe 3 is a layered antiferromagnet which has attracted attention due to its exceptionally high mobility, distinctive unidirectional incommensurate charge density wave (CDW), superconductivity under pressure, and a cascade of magnetic transitions between 7 and 12 K, with as yet unknown order parameters. Here, we use spin-polarized scanning tunneling microscopy to directly image the charge and magnetic orders in GdTe 3 . Below 7 K, we find a striped antiferromagnetic phase with twice the periodicity of the Gd lattice and perpendicular to the CDW. As we heat the sample, we discover a spin density wave with the same periodicity as the CDW between 7 and 12 K; the viability of this phase is supported by our Landau free energy model. Our work reveals the order parameters of the magnetic phases in GdTe 3 and shows how the interplay between charge and spin can generate a cascade of magnetic orders.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Theory for anomalous terahertz emission in striped cuprate superconductors

Recent experiments in the doped cuprates La 2−𝑥 ⁢Ba 𝑥⁢ CuO 4 have revealed the emission of anomalous terahertz radiation after impulsive optical excitation. Here, we theoretically investigate the nonlinear electrodynamics of such striped superconductors and explore the origin of the observed radiation. We argue that photoexcitation is converted into a photocurrent by a second-order optical nonlinearity, which is activated by the breaking of inversion symmetry in certain stripe configurations. We point out the importance of including umklapp photocurrents modulated at the stripe periodicity itself, which impulsively drive surface Josephson plasmons and lead to a resonant structure of outgoing radiation, consistent with the experiments. We speculate on the utility of the proposed mechanism in the context of generating tunable terahertz radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Spin Dynamics of Triple-𝐐 Magnetic Orderings in a Triangular Lattice: Implications for Multi-𝐐 Orderings in General Two-Dimensional Lattices

Multi-𝐐 magnetic structures on two-dimensional (2D) lattices provide a key route to realizing topological physics in 2D magnetism. A major experimental challenge is to unambiguously confirm their formation by excluding the possibility of topologically trivial multidomain single- or double-𝐐 magnetic orders, which cannot be distinguished using conventional diffraction techniques. Here, we propose that long-wavelength spin dynamics offers a universal diagnostic for triangular lattices: Triple-𝐐 orders that preserve rotational symmetry and single- or double-𝐐 orders that break it exhibit qualitatively distinct anisotropies in their Goldstone-mode velocities, stemming from fundamental differences in their underlying spin configurations. We validate this concept using the metallic triangular-lattice antiferromagnet Co 0.325 ⁢TaS 2 , which hosts both a stripe-type single-𝐐 state and a triple-𝐐 tetrahedral ordering at different temperatures. Using inelastic neutron-scattering and spin dynamics simulations, we first refine the spin Hamiltonian by fitting the paramagnetic excitation spectra, allowing us to develop an unbiased model independent of magnetic ordering. We then show that the observed velocity profiles of the Goldstone modes agree with the high-temperature model’s predictions: markedly anisotropic for the single-𝐐 phase and near isotropic for the triple-𝐐 phase. Importantly, this contrast persists across various exchange parameters, highlighting its model-independent nature and suggesting potential applicability to other 2D lattice systems. Beyond the long-wavelength regime, we present a substantial discrepancy between the measured and simulated magnon spectra exclusively in the triple-𝐐 phase. We attribute this discrepancy to magnon energy renormalization arising from order-of-magnitude-enhanced magnon-magnon interactions in the triple-𝐐 phase, due to its noncollinear configuration. This work provides universal insight into the dynamical properties of topological multi-𝐐 magnetic orderings in 2D lattice structures, offering a broadly applicable diagnostic to distinguishing them from topologically trivial single- or double-𝐐 counterparts. The unequivocal confirmation of the triple-𝐐 structure in Co 0.325 ⁢TaS 2 further establishes it as a prominent material platform for exploring topological spin textures in the genuine 2D limit.

Park, Pyeongjae [Oak Ridge National Laboratory (OR↗
DOE OSTI2020

Emergence of a competing stripe phase near the Mott transition in Ti-doped bilayer calcium ruthenates

We report the nanoscale imaging of Ti-doped bilayer calcium ruthenates during the Mott metal-insulator transition by microwave impedance microscopy. Different from a typical first-order phase transition where coexistence of the two terminal phases takes place, a new metallic stripe phase oriented along the in-plane crystalline axes emerges inside both the G-type antiferromagnetic insulating state and the paramagnetic metallic state. The effect of this electronic state can be observed in macroscopic measurements, allowing us to construct a phase diagram that takes into account the energetically competing phases. Our work provides a model approach to correlate the macroscopic properties and mesoscopic phase separation in complex oxide materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

π phase shift across stripes in a charge density wave system

Many strongly correlated materials are characterized by deeply intertwined charge and spin order. Besides their high superconducting transition temperatures, one of the central features of these complex patterns in cuprates is a phase shift which occurs across lines of decreased hole density. That is, when doped away from their antiferromagnetic phase, the additional charge is not distributed uniformly, but rather in “stripes.” The sublattices preferentially occupied by up and down spin are reversed across these stripes, a phenomenon referred to as a “π phase shift.” Many of the spin-charge patterns, including the π phase shift, are reproduced by density matrix renormalization group and quantum Monte Carlo calculations of simplified tight binding (repulsive Hubbard) models. In this paper we demonstrate that this sublattice reversal is generic by considering the corresponding phenomenon in the attractive Hubbard Hamiltonian, where a charge density wave phase forms at half filling. Here, we introduce charge stripes via an appropriate local chemical potential; measurements of charge correlation across the resulting lines of lowered density reveal a clear π phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Stripe antiferromagnetism and disorder in the Mott insulator NaFe 1₋ x Cu x As ( x ≲0.5)

Neutron scattering measurements have demonstrated that the heavily Cu doped NaFe 1₋ x Cu x As compound behaves like a Mott insulator exhibiting both real-space Fe-Cu stripes and antiferromagnetism below a Néel temperature for x ≲ 0.5. In this work, we have investigated the evolution of structural and magnetic ordering using 23 Na and 75 As NMR for single crystals ( x = 0.39 and 0.48), confirming antiferromagnetism in the form of magnetic stripes. We show that end-chain defects in these stripes are the principal source of magnetic disorder and are responsible for cluster spin-glass transitions in both compounds, in the latter case coexistent with antiferromagnetism. Aided by our numerical simulation of the 75 As spectra, we show that a staggered magnetization at the Fe sites is induced by nonmagnetic Cu dopants.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Simulations of wavelength-multiplexed holography for single-shot spatiotemporal characterization of NIF’s advanced radiographic capability (ARC) laser

We simulate the use of a newly developed single-shot wavelength-multiplexed holography-based diagnostic, STRIPED FISH, to fully characterize the as-delivered laser pulses of the National Ignition Facility’s Advanced Radiographic Capability (NIF-ARC) laser. To that end, we have performed simulations of the NIF-ARC pulse incorporating (a) a time-integrated spatial-profile measurement and a complete temporal-intensity-and-phase measurement using a frequency resolved optical gating, but without any spatiotemporal pulse characterizations, and (b) simulated first-order spatiotemporal distortions, which could be measured on a single shot if a STRIPED FISH device were deployed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Novel Charge-Ordered States in 1 T -IrTe 2

1T-IrTe 2 exhibits an intriguing series of charge-ordered states in both bulk and atomically thin layers. The charge orders in IrTe 2 emerge with consecutive first-order structural transitions involving in-plane Ir–Ir dimerization and interlayer Te–Te depolymerization, resulting in stripe patterns with various periods. Upon chemical doping, 1T-IrTe 2 can also be driven into a superconductor. Despite the intense research effort, a comprehensive understanding of the nature of the charge ordering and its relation to the superconductivity is yet to be reached. This review provides an overview of the novel charge orders and the emergence of superconductivity in IrTe 2 . Finally, we further introduce the recent studies on IrTe 2 nanoflake, in which novel charge orders attainable only in two-dimensional limits lay the grounds for an exotic phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Random fields from quenched disorder in an archetype for correlated electrons: The parallel spin stripe phase of La 1.6 – x Nd 0.4 Sr x CuO 4 at the 1/8 anomaly

The parallel stripe phase is remarkable both in its own right, and in relation to the other phases with which it coexists. Its inhomogeneous nature makes such states susceptible to random fields from quenched magnetic vacancies. Here we argue this is the case by introducing low concentrations of nonmagnetic Zn impurities (0%–10%) into La 1.6–x ⁢Nd 0.4⁢ Sr x ⁢CuO 4 (Nd-LSCO) with x=0.125 in single-crystal form, well below the percolation threshold of ~41% for a two-dimensional square lattice. Elastic neutron scattering measurements on these crystals show clear magnetic quasi-Bragg peaks at all Zn dopings. While all the Zn-doped crystals display order parameters that merge into each other and the background at ~68 K, the temperature dependence of the order parameter as a function of Zn concentration is drastically different. This result is consistent with meandering charge stripes within the parallel stripe phase, which are pinned in the presence of quenched magnetic vacancies. In turn it implies vacancies that preferentially occupy sites within the charge stripes, and hence that can be very effective at disrupting superconductivity in Nd-LSCO (x=0.125), and, by extension, in all systems exhibiting parallel stripes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Uniaxial stress study of spin and charge stripes in La1.875Ba0.125CuO4 by 139La NMR and 63Cu NQR

We study the response of spin and charge order in single crystals of La1.875Ba0.125CuO4 to uniaxial stress, through 139La nuclear magnetic resonance (NMR) and 63Cu nuclear quadrupole resonance (NQR), respectively. In unstressed La1.875Ba0.125CuO4, the low-temperature tetragonal structure onsets below TLTT = 57 K, while the charge order and the spin order transition temperatures are TCO = 54 K and TSO = 37 K, respectively. We find that uniaxial stress along the [110] lattice direction strongly suppresses TCO and TSO, but has little effect on TLTT. In other words, under stress along [110] a large splitting (≈ 21 K) opens between TCO and TLTT, showing that these transitions are not tightly linked. On the other hand, stress along [100] causes a slight suppression of TLTT but has essentially no effect on TCO and TSO. Magnetic field H along [110] stabilizes the spin order: the suppression of TSO under stress along [110] is slower under H ∥ [110] than H ∥ [001]. We develop a Landau free energy model and interpret our findings as an interplay of symmetry breaking terms driven by the orientation of spins.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Two-Dimensional Superconducting Fluctuations Associated with Charge-Density-Wave Stripes in La 1.87 ⁢Sr 0.13 ⁢Cu 0.99 ⁢Fe 0.01 ⁢O 4

The presence of a small concentration of in-plane Fe dopants in La 1.87 Sr 0.13 Cu 0.99 Fe 0.01 O 4 is known to enhance stripelike spin and charge density wave (SDW and CDW) order and suppress the superconducting T c . Here, we show that it also induces highly two-dimensional superconducting correlations that have been argued to be the signatures of a new form of superconducting order, the so-called pair density wave (PDW) order. In addition, using resonant soft x-ray scattering, we find that the two-dimensional superconducting fluctuation is strongly associated with the CDW stripe. In particular, the PDW signature first appears when the correlation length of the CDW stripe grows over eight times the lattice unit (~8 a). In conclusion, these results provide critical conditions for the formation of the PDW order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Magnetic structure and Ising-like antiferromagnetism in the bilayer triangular lattice compound NdZnPO

Here, the complex interplay of spin frustration and quantum fluctuations in low-dimensional quantum materials leads to a variety of intriguing phenomena. This research focuses on a detailed analysis of the magnetic behavior exhibited by NdZnPO, a bilayer spin-1/2 triangular lattice antiferromagnet. The investigation employs magnetization, specific heat, and powder neutron scattering measurements. At zero field, a long-range magnetic order is observed at T N = 1.64 K. Powder neutron diffraction experiments show the Ising-like magnetic moments along the c-axis, revealing a stripe like magnetic structure with magnetic propagation vector (1/2, 0, 1/2). Application of a magnetic field along the c-axis suppresses the antiferromagnetic order, leading to a fully polarized ferromagnetic state above B c = 4.5 T. This transition is accompanied by notable enhancements in the nuclear Schottky contribution. Moreover, the absence of spin frustration and expected field-induced plateau-like phases are remarkable observations. Detailed calculations of magnetic dipolar interactions revealed complex couplings reminiscent of a honeycomb lattice, suggesting the potential emergence of Kitaev-like physics within this system. This comprehensive study of the magnetic properties of NdZnPO highlights unresolved intricacies, underscoring the imperative for further exploration to unveil the underlying governing mechanisms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗