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DOE OSTI2025

Hamiltonian parameter inference from resonant inelastic x-ray scattering with active learning

Identifying model Hamiltonians is a vital step toward creating predictive models of materials. Here, in this study, we combine Bayesian optimization with the EDRIXS numerical package to infer Hamiltonian parameters from resonant inelastic x-ray scattering (RIXS) spectra within the single atom approximation. To evaluate the efficacy of our method, we test it on experimental RIXS spectra of NiPS 3 , NiCl 2 , Ca 3 ⁢LiOsO 6 , and Fe 2⁢ O 3 , and demonstrate that it can reproduce results obtained from hand-fitted parameters to a precision similar to expert human analysis while providing a more systematic mapping of parameter space. Our work provides a key first step toward solving the inverse scattering problem to extract effective multi-orbital models from information-dense RIXS measurements, which can be applied to a host of quantum materials. We also propose atomic model parameter sets for two materials, Ca 3⁢ LiOsO 6 and Fe 2⁢ O 3 , that were previously missing from the literature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Dark Matter Constraints from Isomeric 178⁢m Hf

In this article, we describe a first measurement of the radiation from a 178⁢m Hf sample to search for dark matter. The $\gamma$ flux from this sample, possessed by Los Alamos National Laboratory nuclear chemistry, was measured with a Ge detector at a distance of 1.2 m due to its high activity. We search for $\gamma$’s that cannot arise from the radioactive decay of 178⁢m Hf but might arise from the production of a nuclear state due to the inelastic scattering with dark matter. The limits obtained on this $\gamma$ flux are then translated into constraints on the parameter space of inelastic dark matter. Finally, we describe the potential reach of future studies with 178⁢m Hf.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Inelastic dark matter scattering off Thallium cannot save DAMA

We study the compatibility of the observed DAMA modulation signal with inelastic scattering of dark matter (DM) off of the 0.1% Thallium (Tl) dopant in DAMA. In this work we test whether there exist regions of parameter space where the Tl interpretation gives a good fit to the most recent data from DAMA, and whether these regions are compatible with the latest constraints from other direct detection experiments. Previously, Chang et al. in 2010, had proposed the Tl interpretation of the DAMA data, and more recently (in 2019) the DAMA/LIBRA collaboration found regions in parameter space of Tl inelastic scattering that differ by more than 10σ from a no modulation hypothesis. We have expanded upon their work by testing whether the regions of parameter space where inelastic DM-Tl scattering gives a good fit to the most recent DAMA data survive the constraints placed by the lack of a DM signal in XENON1T and CRESST-II. In addition, we have tested how these regions change with the main sources of uncertainty: the Tl quenching factor, which has never been measured directly, and the astrophysical uncertainties in the DM distribution. We conclude that inelastic DM scattering off Tl cannot explain the DAMA data in light of null results from other experiments.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Neutrino constraints on inelastic dark matter captured in the Sun

Abstract The flux of neutrinos from annihilation of gravitationally captured dark matter in the Sun has significant constraints from direct-detection experiments. However, these constraints are relaxed for inelastic dark matter as inelastic dark matter interactions generate less energetic nuclear recoils compared to elastic dark matter interactions. In this paper, we explore the possibility for large volume underground neutrino experiments to detect the neutrino flux from captured inelastic dark matter in the Sun. The neutrino spectrum has two components: a mono-energetic “spike” from pion and kaon decays at rest and a broad-spectrum “shoulder” from prompt primary meson decays. We focus on detecting the shoulder neutrinos from annihilation of hadrophilic inelastic dark matter with masses in the range 4–100 GeV and the mass splittings in up to 300 keV. We determine the event selection criterion for DUNE to identify GeV-scale muon neutrinos and anti-neutrinos originating from hadrophilic dark matter annihilation in the Sun, and forecast the sensitivity from contained events. We also map the current bounds from Super-Kamiokande and IceCube on elastic dark matter, as well as the projected limits from Hyper-Kamiokande, to the parameter space of inelastic dark matter. We find that there is a region of parameter space that these neutrino experiments are more sensitive to than the direct-detection experiments. For dark matter annihilation to heavy-quarks, the projected sensitivity of DUNE is weaker than current (future) Super (Hyper) Kamiokande experiments. However, for the light-quark channel, only the spike is observable and DUNE will be the most sensitive experiment.

Astronomy & Astrophysics↗

DOE OSTI2024

Revealing the unusual rate-dependent mechanical behaviors of nematic liquid crystal elastomers

Liquid crystal elastomers (LCEs) exhibit unique mechanical properties of soft elasticity and enhanced energy dissipation with rate dependency. They are potentially transformative materials for applications in mechanical impact mitigation and vibration isolation. However, previous studies have primarily focused on the mechanics of LCEs under equilibrium and quasistatic loading conditions. Critical knowledge gaps exist in understanding their rate-dependent behaviors, which are a complex mixture of traditional network viscoelasticity and the soft elastic behaviors with changes in the mesogen orientation and order parameter. Together, these inelastic mechanisms lead to unusual rate-dependent energy absorption responses of LCEs. In this work, we developed a viscoelastic constitutive theory for monodomain nematic LCEs to investigate how multiple underlying sources of inelasticity manifest in the rate-dependent and dissipative behaviors of monodomain LCEs. Here, the theoretical modeling framework combines the neo-classical network theory with evolution rules for the mesogen orientation and order parameter with conventional viscoelasticity. The model is calibrated with uniaxial tension and compression data spanning six decades of strain rates. The established 3D constitutive model enables general loading predictions taking the initial mesogen orientation and order parameter as inputs. Additionally, parametric studies were performed to further understand the rate dependence of monodomain LCEs in relation to their energy absorption characteristics. Based on the parametric studies, particularly loading scenarios are identified as conditions where LCEs outperform conventional elastomers regarding energy absorption.

42 ENGINEERING↗

DOE OSTI2023

Capturing dynamical correlations using implicit neural representations

Abstract Understanding the nature and origin of collective excitations in materials is of fundamental importance for unraveling the underlying physics of a many-body system. Excitation spectra are usually obtained by measuring the dynamical structure factor, S ( Q , ω ), using inelastic neutron or x-ray scattering techniques and are analyzed by comparing the experimental results against calculated predictions. We introduce a data-driven analysis tool which leverages ‘neural implicit representations’ that are specifically tailored for handling spectrographic measurements and are able to efficiently obtain unknown parameters from experimental data via automatic differentiation. In this work, we employ linear spin wave theory simulations to train a machine learning platform, enabling precise exchange parameter extraction from inelastic neutron scattering data on the square-lattice spin-1 antiferromagnet La 2 NiO 4 , showcasing a viable pathway towards automatic refinement of advanced models for ordered magnetic systems.

36 MATERIALS SCIENCE↗

DOE OSTI2024

𝐽/𝜓 photoproduction and polarization in 𝑒 + 𝑝 collisions in the improved color evaporation model

We calculate the production and polarization of direct 𝐽/𝜓 in the improved color evaporation model in 𝑒 + 𝑝 photoproduction. We present the production as functions of transverse momentum, mass of the hadronic final state, and inelasticity. We also present the polarization parameters 𝜆 𝜗 , 𝜆 𝜑 , and 𝜆 𝜗⁢𝜑 in the helicity and the Collins-Soper frames, as well as the frame-invariant polarization parameter $\tilde{𝜆}$ as a function of transverse momentum and inelasticity. We find agreement with both 𝐽/𝜓 unpolarized cross sections and the invariant polarization parameters as a function of 𝑝𝑇.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

Quantifying the phase diagram and Hamiltonian of S = 1/2 kagome antiferromagnets: bridging theory and experiment

Spin-1/2 kagome antiferromagnets are leading candidates for realizing quantum spin liquid (QSL) ground states. While QSL ground states are predicted for the pure Heisenberg model, understanding the robustness of the QSL to additional interactions that may be present in real materials is a forefront question in the field. Here we employ large-scale density-matrix renormalization group simulations to investigate the effects of next-nearest neighbor exchange couplings J 2 and Dzyaloshinskii-Moriya interactions D, which are relevant to understanding the prototypical kagome materials herbertsmithite and Zn-barlowite. By utilizing clusters as large as XC12 and extrapolating the results to the thermodynamic limit, we precisely delineate the scope of the QSL phase, which remains robust across an expanded parameter range of J 2 and D. Direct comparison of the simulated static and dynamic spin structure factors with inelastic neutron scattering reveals the parameter space of the Hamiltonians for herbertsmithite and Zn-barlowite, and, importantly, provides compelling evidence that both materials exist within the QSL phase. These results establish a powerful convergence of theory and experiment in this most elusive state of matter.

Jiang, Shengtao [SLAC National Accelerator Laborat↗

DOE OSTI2024

Structural and magnetic characterization of CeTa 7 ⁢O 19 and YbTa 7 ⁢ O 19 with a two-dimensional pseudospin-$\frac{1}{2}$ triangular lattice

Triangular lattice antiferromagnets are prototypes for frustrated magnetism and may potentially realize novel quantum magnetic states such as a quantum spin-liquid ground state. A recent work suggests NdTa 7 ⁢O 19 with rare-earth triangular lattice is a quantum spin-liquid candidate and highlights the large family of rare-earth heptatantalates as a framework for quantum magnetism investigation. Here, in this paper, we report the structural and magnetic characterization of CeTa 7 ⁢ O 19 and YbTa 7 ⁢ O 19 . Both compounds are isostructural to NdTa 7 ⁢O 19 with no detectable structural disorder. For CeTa 7 ⁢O 19 , the crystal field energy levels and parameters are determined by inelastic neutron scattering measurements. Based on the crystal field result, the magnetic susceptibility data could be well fitted and explained, which reveals that CeTa 7 ⁢O 19 is a highly anisotropic Ising triangular-lattice antiferromagnet (𝑔 𝑧 ⁡/𝑔 𝑥⁢𝑦 ∼ 3) with very weak exchange interaction (J ∼ 0.22 K). For YbTa 7⁢ O 19 , millimeter-sized single crystals could be grown. The anisotropic magnetization and electron spin resonance data show that YbTa 7⁢ O 19 has a contrasting in-plane magnetic anisotropy with 𝑔 𝑧 ⁡/𝑔 𝑥⁢𝑦 ∼ 0.67 similar as that of YbMgGaO 4 . The above results indicate that CeTa7⁢ O 19 and YbTa 7 ⁢O 19 with pseudospin-1/2 ground states might either be quantum spin-liquid candidate materials or find applications in adiabatic demagnetization refrigeration due to the weak exchange interaction.

Pan, Feihao↗

DOE OSTI2021

Bayesian analysis for estimating statistical parameter distributions of elasto-viscoplastic material models

High temperature design methods rely on constitutive models for inelastic deformation and failure typically calibrated against the mean of experimental data without considering the associated scatter. Variability may arise from the experimental data acquisition process, from heat-to-heat material property variations, or both and need to be accurately captured to predict parameter bounds leading to efficient component design. Applying the Bayesian Markov Chain Monte Carlo (MCMC) method to produce statistical models capturing the underlying uncertainty in the experimental data is an area of ongoing research interest. This work varies aspects of the Bayesian MCMC method and explores their effect on the posterior parameter distributions for a uniaxial elasto-viscoplastic damage model using synthetically generated reference data. From our analysis with the uniaxial inelastic model we determine that an informed prior distribution including different types of test conditions results in more accurate posterior parameter distributions. The parameter posterior distributions, however, do not improve when increasing the number of similar experimental data. Additionally, changing the amount of scatter in the data affects the quality of the posterior distributions, especially for the less sensitive model parameters. Moreover, we perform a sensitivity study of the model parameters against the likelihood function prior to the Bayesian analysis. The results of the sensitivity analysis help to determine the reliability of the posterior distributions and reduce the dimensionality of the problem by fixing the insensitive parameters. The comprehensive study described in this work demonstrates how to efficiently apply the Bayesian MCMC methodology to capture parameter uncertainties in high temperature inelastic material models. Quantifying these uncertainties in inelastic models will improve high temperature engineering design practices and lead to safer, more effective component designs.

42 ENGINEERING↗

DOE OSTI2020

A Physically-Based Model for Thermo-Oxidative and Hydrolytic Aging of Elastomers

A computationally efficient model is proposed to capture the loss of mechanical performance due to chemical aging that are formed as the competition of chain scission and cross-link formation/dissolution, such as thermo-oxidative aging or hydrolytic aging. The model should be considered an extension of our recent models [1, 2, 3] which further simplifies the matrix behavior based on the assumption of independence of environmental and mechanical damage. The model uses this assumption to reduce the necessary material parameters needed to model constitutive and inelastic behavior of elastomers during aging. To this end, the model can provide accurate predictions of the material performance with the significantly fewer number of fitting parameters. The model is relevant for all decay mechanisms formed by the occurrence of two simultaneous micro-mechanisms; (i) formation/reduction of the cross-links, and (ii) chain scission, both of which are present in thermo-oxidation and hydrolytic aging. Assuming the alteration of the chain density along the aging trajectory is identical to the peroxide cross-link density for thermo-oxidation, and the change of the average molecular weight for hydrolysis, the strain energy of polymer matrix can be rewritten as a function of deformation, deformation history, storage time and aging temperature. Next, the modified network alteration model is formulated for implementation into Finite Element (FE) simulations. The model is built on the presumption of homogeneous and consistent oxygen/water absorption and thus is mainly relevant for relatively thin samples exposed to environmental loads for a long time. The proposed model includes only six physically inspired material parameters. Therefore, while it is computationally efficient, it shows good agreement with own experimental data, which performed on various range of accelerated aging temperatures and times. With respect to its computational efficiency, simplicity, accuracy, and interpret-ability, the model is the right choice for advanced implementations in FE programs.

42 ENGINEERING↗

DOE OSTI2025

Ionization-driven competitive (recovery) process in pre-damaged KTaO 3 : A brief review

The nuclear (S n ) and electronic (S e ) energy dissipation processes have been considered to be independent and largely uncorrelated, influencing our understanding of ion–solid interaction and damage processes in the last decades. Recently, however, it has become more generally accepted that S n and S e are coupled as they interact both in time and space. To decouple these processes, separating these effects in experiments using sequential dual-beam irradiations have become accepted as the logical path to advance the understanding of complex interactions between S e and pre-existing defects that may be created from displacement events. This experimental approach has been recently applied to studies of KTaO 3 to reveal new insights into this critical research topic. Here, we offer a forward-looking and comprehensive perspective on the fundamental coupling between Se and pre-existing defects in KTaO 3 . The origins behind the competitive two-stage phase transition process leading to damage healing are revealed and discussed. Furthermore, the evidence resulting from synergistic effects is also included for comparison. Additionally, our findings are rationalized using both Se and the ion velocity as key parameters. We highlight how the inelastic thermal spike (i-TS) calculations provide insights into the nature of this coupled process and further confirm that the ion velocity effect governs annealing kinetics. This work emphasizes that through the introduction of a small amount of local disorder in materials, MeV ion irradiation (i.e., not extreme S e ) may also be one additional option in subsequent material modification and functionalization.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2022

Modeling Sequences of Earthquakes and Aseismic Slip (SEAS) in Elasto-Plastic Fault Zones With a Hybrid Finite Element Spectral Boundary Integral Scheme

We present a coupled finite element spectral boundary integral framework for modeling sequences of earthquakes and aseismic slip on a 2-D planar rate-and-state fault with off-fault visco-plastic response in the plane strain approximation. The model resolves both slow aseismic deformation and inertia effects during rapid slip. As an application, we perform two sets of simulations with different choices of cohesion to explore the co-evolution of fault slip, bulk plasticity and local stress fields. The first set implements a relatively large value of the cohesion parameter, which results in limiting inelastic strain accumulation to dynamic rupture phases. The second set implements a smaller cohesion, allowing for plastic strain to accumulate in both seismic and aseismic phases. For the first model, our results indicate that the extent and distribution of plastic strain depend on the angle of maximum compressive principal stress. At larger angles, inelastic strain accumulates on the extensional side of a dynamically propagating rupture. At smaller angles, the extent of plasticity is limited to the compressional side of the domain. At smaller cohesion values, off-fault plasticity may occur during aseismic slip, which alters the nucleation characteristics and earthquake sequence pattern. Furthermore, our results at lower cohesion values indicate that plastic strain accumulation may occur in both the extensional and compressional sides of the off-fault bulk even at higher angles of maximum compression. In conclusion, this produces damage patterns that deviate from the traditional off-fault fan-like distribution observed in dynamic rupture simulations and emphasizes the significance of long-term deformation in interpreting observations.

58 GEOSCIENCES↗

DOE OSTI2020

Dynamic pair-breaking current, critical superfluid velocity, and nonlinear electromagnetic response of nonequilibrium superconductors

Here, we report numerical calculations of a dynamic pair-breaking current density $J_d$ and a critical superfluid velocity $v_d$ in a nonequilibrium superconductor carrying a uniform, large-amplitude AC current density $J(t) = J_a$sinΩ$\textit{t}$ with Ω well below the gap frequency Ω $\ll Δ_0/ℏ$. The dependencies $J_d$(Ω, $\textit{T}$) and $v_d$(Ω, $\textit{T}$) near the critical temperature $T_c$ were calculated from either the full time-dependent nonequilibrium equations for a dirty $\textit{s}$-wave superconductor or the time-dependent Ginzburg-Landau (TDGL) equations for a gapped superconductor, taking into account the GL relaxation time of the order parameter $τ_{\text{GL}}$ and the inelastic electron-phonon relaxation time of quasiparticles $τ_E$. We show that both approaches give similar frequency dependencies of $J_d$(Ω) and $v_d$(Ω) which gradually increase from their static pair-breaking GL values $J_c$ and $v_c$ at Ω$τ_E \ll$1 to $\sqrt{2}J_c$ and $\sqrt{2}v_c$ at Ω$τ_E \gg$ 1. Here $J_d, v_d$ and a dynamic superheating field at which the Meissner state becomes unstable were calculated in two different regimes of a fixed AC current and a fixed AC superfluid velocity induced by the applied AC magnetic field $H = H_a$ sinΩ$\textit{t}$ in a thin superconducting filament or a type-II superconductor with a large GL parameter. We also calculated a nonlinear electromagnetic response of a nonequilibrium superconducting state, particularly a dynamic kinetic inductance and a dissipative quasiparticle conductivity, taking into account the oscillatory dynamics of superconducting condensate and the kinetics of quasiparticles driven by a strong AC current. It is shown that an AC current density produces multiple harmonics of the electric field, the amplitudes of the higher-order harmonics diminishing as $τ_E$ increases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

An iron evaluation story: from TALYS model parameters to validation on the ASPIS benchmark with the Monte-Carlo code TRIPOLI-4

Iron is a widespread structural material in nuclear applications. However some benchmark studies show that for many libraries, including TENDL-2019, producing good iron evaluations is still an open challenge. This work aims at improving TENDL-2019 {sup 56}Fe and {sup 54}Fe evaluations through feedbacks from experimental data and Monte Carlo results of the iron benchmark ASPIS. Part of the T6 code infrastructure was used to produce the evaluations. In the new evaluations, particular attention to resonance parameters and formalism was paid to address the importance of elastic scattering. The total inelastic scattering and inelastic continuum cross sections were shaped by modifying the input parameters of TALYS, one of the T6 codes. Additionally, it was necessary to normalise some reaction channels to those of JENDL-4.0. With the new files ASPIS results, obtained with the Monte Carlo code TRIPOLI-4, improved noticeably compared to TENDL 2019. The evaluations and parameter setting modifications are to be included into TENDL-2021. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2023

Coherent detection of hidden spin–lattice coupling in a van der Waals antiferromagnet

Strong interactions between different degrees of freedom lead to exotic phases of matter with complex order parameters and emergent collective excitations. Conventional techniques, such as scattering and transport, probe the amplitudes of these excitations, but they are typically insensitive to phase. Therefore, novel methods with phase sensitivity are required to understand ground states with phase modulations and interactions that couple to the phase of collective modes. Here, by performing phase-resolved coherent phonon spectroscopy (CPS), we reveal a hidden spin–lattice coupling in a vdW antiferromagnet FePS 3 that eluded other phase-insensitive conventional probes, such as Raman and X-ray scattering. With comparative analysis and analytical calculations, we directly show that the magnetic order in FePS 3 selectively couples to the trigonal distortions through partially filled t 2 g orbitals. This magnetoelastic coupling is linear in magnetic order and lattice parameters, rendering these distortions inaccessible to inelastic scattering techniques. Our results not only capture the elusive spin–lattice coupling in FePS 3 but also establish phase-resolved CPS as a tool to investigate hidden interactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Reviving MeV-GeV indirect detection with inelastic dark matter

Thermal relic dark matter below ∼ 10 GeV is excluded by cosmic microwave background data if its annihilation to visible particles is unsuppressed near the epoch of recombination. Usual model-building measures to avoid this bound involve kinematically suppressing the annihilation rate in the low-velocity limit, thereby yielding dim prospects for indirect detection signatures at late times. In this work, we investigate a class of cosmologically viable sub-GeV thermal relics with late-time annihilation rates that are detectable with existing and proposed telescopes across a wide range of parameter space. We study a representative model of inelastic dark matter featuring a stable state χ 1 and a slightly heavier excited state χ 2 whose abundance is thermally depleted before recombination. Since the kinetic energy of dark matter in the Milky Way is much larger than it is during recombination, χ 1 χ 1 → χ 2 χ 2 upscattering can efficiently regenerate a cosmologically long-lived Galactic population of χ 2 , whose subsequent coannihilations with χ 1 give rise to observable gamma-rays in the ∼ 1 MeV − 100 MeV energy range. We find that proposed MeV gamma-ray telescopes, such as e-ASTROGAM, AMEGO, and MAST, would be sensitive to much of the thermal relic parameter space in this class of models and thereby enable both discovery and model discrimination in the event of a signal at accelerator or direct detection experiments. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Implicit neural representations for experimental steering of advanced experiments

Scattering measurements using electrons, neutrons, or photons are essential for obtaining microscopic insights into materials. However, limited facility availability and high-dimensional scattering data necessitate more efficient experimental steering techniques. Here, we report a machine learning method that guides scattering data collection and facilitates real-time estimation of model parameters, given a reliable forward model to simulate experimental signals. We employ implicit neural representations as efficient surrogates that link model parameters with simulated spectroscopies. This enables a Bayesian optimal experimental design framework to estimate the probability distributions of parameters from high-dimensional scattering data. We demonstrate the proposed method using inelastic neutron scattering with simulated and real experimental data, highlighting the method’s ability to provide real-time parameter estimation with quantified uncertainties and to deliver informed experimental guidance that reduces experimental time while maximizing scientific output. This approach paves the way for accelerated discoveries in condensed matter through scattering measurements.

36 MATERIALS SCIENCE↗