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DOE OSTI2022

Discovery of two-dimensional binary nanoparticle superlattices using global Monte Carlo optimization

Binary nanoparticle (NP) superlattices exhibit distinct collective plasmonic, magnetic, optical, and electronic properties. Here, we computationally demonstrate how fluid-fluid interfaces could be used to self-assemble binary systems of NPs into 2D superlattices when the NP species exhibit different miscibility with the fluids forming the interface. We develop a basin-hopping Monte Carlo (BHMC) algorithm tailored for interface-trapped structures to rapidly determine the ground-state configuration of NPs, allowing us to explore the repertoire of binary NP architectures formed at the interface. By varying the NP size ratio, interparticle interaction strength, and difference in NP miscibility with the two fluids, we demonstrate the assembly of an array of exquisite 2D periodic architectures, including AB-, AB 2 -, and AB 3 -type monolayer superlattices as well as AB-, AB 2 -, A 3 B 5 -, and A 4 B 6 -type bilayer superlattices. Our results suggest that the interfacial assembly approach could be a versatile platform for fabricating 2D colloidal superlattices with tunable structure and properties.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Localization in the SCAN meta-generalized gradient approximation functional leading to broken symmetry ground states for graphene and benzene

Density functional theory calculations play a central role in understanding chemical and solid-state systems. Progress depends on density functionals that accurately reproduce both energies, for thermochemistry, and properly describe ground states and other properties that are of interest. The Cr dimer, benzene and graphene are especially important benchmark systems for quantum chemistry and condensed matter physics. The Strongly Constrained and Appropriately Normed (SCAN) functional, which is an advanced meta-generalized gradient approximation functional that significantly improves molecular energies is shown to perform poorly for the Cr dimer. This is connected with its poor performance for itinerant solid-state magnets and is a consequence of over localization of electrons, thus illustrating an analogy between the Cr dimer and itinerant magnets. The Cr dimer is a notoriously difficult system for density functionals. However, we additionally find that SCAN predicts an incorrect symmetry broken ground state for 2D graphene and for the benzene molecule, which is surprising considering that ground states of these are known to be well described even by the simplest local density approximation. We show that SCAN overly favors localized spin polarized states, which is a serious deficiency of this approach. Thus, the challenge of finding density functionals that accurately treat both localized and delocalized electronic systems remains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Loss of energetic ions due to n = 1 internal kink instability in HL-2M

Effects of three-dimensional (3D) perturbations due to an unstable n = 1 (n is the toroidal mode number) internal kink (IK) on the energetic particles (EPs) are systematically investigated for the HL-2M tokamak, utilizing the MARS-F/K code and a recently developed test particle tracing module. A high-beta sawteething HL-2M scenario, simulated by the TRANSP code, is chosen for this study. In general, the 3D perturbation associated with an unstable IK is found to affect the EP drift orbit, confinement, and loss in HL-2M. The instability-induced EP loss fraction is found to be typically less than 10%, without counting for the prompt orbit loss associated with the 2D equilibrium field for counter-current particles. The latter reaches about 16% in HL-2M. For co-current EPs, a 100 G 3D magnetic field (inside the plasma) due to the IK does not induce any EP loss assuming a static perturbation. A sawtooth-like time-varying perturbation field, with the peak amplitude reaching 1000 G, can however produce about 30% loss for the co-current EPs in HL-2M. The majority of lost EPs tend to strike the lower divertor region, with a small fraction of particles striking the low-field side mid-plane region of the limiting surface.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Simulation of plasma transport in MPS-LD linear plasma device by using BOUT++

Here a linear plasma device (LPD) module based on the 2D transport module under the BOUT++ framework is developed in this paper to simulate plasma transport in the LPD. The LPD module includes three parts, i.e. magnetic field calculation, simulation mesh generation and plasma transport setup. The magnetic field is calculated with the circular current loop using the location and current information of each coil. The mesh generation code can produce a simulation mesh for LPD by employing the magnetic field. The plasma transport model is based on the reduced Braginskii equations, which consist of the continuity equation, momentum equation, and energy equation. The fluid neutral model is applied for neutral particle simulation. Deuterium (D) and helium (He) ions and atoms can be simulated by the model. The first attempt to simulate plasma transport in the new LPD, called multiple plasma simulation linear plasma device (MPS-LD), is presented using the developed model. The D plasma transport in the MPS-LD is simulated and benchmarked against the two-point model, showing the validation of the BOUT++ simulation. The effects of radial transport on the heat load to the target are studied, which illustrates the significant impact of the radial diffusivities $D_⟂$ and $\mathcal{X}_{⟂i,e}$ on the plasma. Moreover, the He impurity injection process during the discharge is studied with emphasis on plasma–impurity interactions. The simulation results show that He injection can reduce the plasma energy load to the target significantly, and the efficiency depends on the He source density and injection velocity. The present work provides an alternative and flexible simulation tool for plasma transport in LPDs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2023

The 17 April 2021 Widespread Solar Energetic Particle Event

A complex and long-lasting solar eruption on 17 April 2021 produced a widespread solar energetic particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere that covered distances to the Sun from 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event was the second widespread SEP event detected in solar cycle 25, and it produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare that showed multiple hard X-ray peaks over a duration of one hour. The event was further accompanied by a medium-fast coronal mass ejection (CME) with a speed of 880 km s -1 that drove a shock, an extreme ultraviolet wave, and long-lasting and complex radio burst activity that showed four distinct type III burst groups over a period of 40 min. We aim to understand the reason for the wide spread of elevated SEP intensities in the inner heliosphere as well as identify the underlying source regions of the observed energetic electrons and protons. We applied a comprehensive multi-spacecraft analysis of remote-sensing observations and in situ measurements of the energetic particles and interplanetary context to attribute the SEP observations at the different locations to the various potential source regions at the Sun. We used an ENLIL simulation to characterize the complex interplanetary state and its role in the energetic particle transport. The magnetic connection between each spacecraft and the Sun was determined using ballistic backmapping in combination with potential field source surface extrapolations in the lower corona. Using also a reconstruction of the coronal shock front, we then determined the times when the shock establishes magnetic connections with the different observers. Radio observations were used to characterize the directivity of the four main injection episodes, which were then employed in a 2D SEP transport simulation to test the importance of these different injection episodes. A comprehensive timing analysis of the inferred solar injection times of the SEPs observed at each spacecraft suggests different source processes being important for the electron and proton events. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source for the electron event. In contrast to earlier studies on widespread SEP events, we find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110 o covered by distinct SEP injections, which is also supported by our SEP transport modeling.

sun↗

DOE OSTI2022

Electrical Manipulation of Topological Phases in a Quantum Anomalous Hall Insulator

Quantum anomalous Hall phases arising from the inverted band topology in magnetically doped topological insulators have emerged as an important subject of research for quantization at zero magnetic fields. Though necessary for practical implementation, sophisticated electrical control of molecular beam epitaxy (MBE)-grown quantum anomalous Hall matter have been stymied by growth and fabrication challenges. Here, in this study, a novel procedure is demonstrated, employing a combination of thin-film deposition and 2D material stacking techniques, to create dual-gated devices of the MBE-grown quantum anomalous Hall insulator, Cr-doped (Bi,Sb) 2 Te 3 . In these devices, orthogonal control over the field-induced charge density and the electric displacement field is demonstrated. A thorough examination of material responses to tuning along each control axis is presented, realizing magnetic property control along the former and a novel capability to manipulate the surface exchange gap along the latter. Through electrically addressing the exchange gap, the capabilities to either strengthen the quantum anomalous Hall state or suppress it entirely and drive a topological phase transition to a trivial state are demonstrated. The experimental result is explained using first principle theoretical calculations, and establishes a practical route for in situ control of quantum anomalous Hall states and topology.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Using Direct Laboratory Measurements of Electron Temperature Anisotropy to Identify the Heating Mechanism in Electron-Only Guide Field Magnetic Reconnection

Anisotropic electron heating during electron-only magnetic reconnection with a large guide magnetic field is directly measured in a laboratory plasma through in situ measurements of electron velocity distribution functions. Electron heating preferentially parallel to the magnetic field is localized to one separatrix, and anisotropies of 1.5 are measured. The mechanism for electron energization is identified as the parallel reconnection electric field because of the anisotropic nature of the heating and spatial localization. These characteristics are reproduced in a 2D particle-in-cell simulation and are also consistent with numerous magnetosheath observations. A measured increase in the perpendicular temperature along both separatrices is not reproduced by our 2D simulations. Here, this work has implications for energy partition studies in magnetosheath and laboratory reconnection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Large Magnetic Gap in a Designer Ferromagnet–Topological Insulator–Ferromagnet Heterostructure

Abstract Combining magnetism and nontrivial band topology gives rise to quantum anomalous Hall (QAH) insulators and exotic quantum phases such as the QAH effect where current flows without dissipation along quantized edge states. Inducing magnetic order in topological insulators via proximity to a magnetic material offers a promising pathway toward achieving the QAH effect at a high temperature for lossless transport applications. One promising architecture involves a sandwich structure comprising two single‐septuple layers (1SL) of MnBi 2 Te 4 (a 2D ferromagnetic insulator) with ultrathin few quintuple layer (QL) Bi 2 Te 3 in the middle, and it is predicted to yield a robust QAH insulator phase with a large bandgap greater than 50 meV. Here, the growth of a 1SL MnBi 2 Te 4 /4QL Bi 2 Te 3 /1SL MnBi 2 Te 4 heterostructure via molecular beam epitaxy is demonstrated and the electronic structure probed using angle‐resolved photoelectron spectroscopy. Strong hexagonally warped massive Dirac fermions and a bandgap of 75 ± 15 meV are observed. The magnetic origin of the gap is confirmed by the observation of the exchange‐Rashba effect, as well as the vanishing bandgap above the Curie temperature, in agreement with density functional theory calculations. These findings provide insights into magnetic proximity effects in topological insulators and reveal a promising platform for realizing the QAH effect at elevated temperatures.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Many-Body Exciton and Intervalley Correlations in Heavily Electron-Doped WSe 2 Monolayers

We shoe that in monolayer transition-metal dichalcogenide semiconductors, many-body correlations can manifest in optical spectra when electron-hole pairs (excitons) are photoexcited into a 2D Fermi sea of mobile carriers. At low carrier densities, the formation of charged excitons (X ± ) is well documented. However, in WSe 2 monolayers, an additional absorption resonance, often called X -' , emerges at high electron density. Its origin is not understood. Here, we investigate the X -' state via polarized absorption spectroscopy of gated WSe 2 monolayers in magnetic fields to 60T. Field-induced filling and emptying of the lowest optically active Landau level in the K ' valley causes repeated quenching of the corresponding optical absorption. Surprisingly, these quenchings are accompanied by absorption changes to higher Landau levels in both K ' and K valleys, which are unoccupied. These results cannot be reconciled within a single-particle picture, and demonstrate the many-body nature and intervalley correlations of the X -' quasiparticle state.

2D materials↗

DOE OSTI2025

Magnetic semiconductors from functionalized Cr 2 ⁢C MXenes

Here, we report an ab initio investigation of functionalized and 3⁢𝑑-electron-doped Cr 2 ⁢C MXenes. Upon functionalization, the Cr 2⁢ C becomes chemically, dynamically, and mechanically stable, and it exhibits magnetic semiconducting behavior. Cr 2 ⁢CF 2 stands out as a wide band gap semiconductor, possessing superexchange interaction mediated by F atoms within the layer; however, the applied strain transforms it from an indirect to a direct band gap semiconductor. Strong spin-phonon coupling found in Cr 2 ⁢CH 2 is supported by the distorted Cr spin density due to the hydrogen environment. Two magnon branches, associated with two sublattice spins, are found in the ferromagnetic Cr 2 ⁢CO 2 and antiferromagnetic Cr 2 ⁢CF 2 . Depending on the types of 3⁢𝑑-electron dopants and functionalization, Cr 2 ⁢C MXenes (except for Cr 2 ⁢CO 2 ) change from an indirect band gap magnetic semiconductor to different states of electronic and magnetic matter, including an exotic direct band gap magnetic bipolar semiconductor. In addition, we reveal a band inversion between the two highest valence bands in the Fe-doped Cr 2 ⁢CCl 2 .

2D materials↗

DOE OSTI2022

Development and validation of a quantitative proton NMR method for the analysis of pregnenolone

Pregnenolone (PREG) is an endogenous steroid frequently sold as an over-the-counter dietary supplement touted to promote neurological and immunological health. While the PREG dietary supplement is added to the diet for health benefits, there are no FDA approved PREG drugs. However, compounded PREG drug products are available to U.S. patients. The FDA works with state regulatory authorities on the oversight of compounding activities, including developing 503A and 503B lists of bulk substances that compounders are permitted to use. PREG is one of the substances publicly nominated to be included on the 503B list. Compounded hormone therapies such as those using PREG are of interest given the lack of standardization in compounded drug products which may increase the possibility of underdosing, overdosing, or contamination. However, no USP monograph currently exists to evaluate the quality of PREG drug substance or product. To address knowledge gaps and assist in quality control, a simple and rapid quantitative proton nuclear magnetic resonance spectroscopy (qNMR) method for the identification and assay of PREG in different types of PREG products was developed and validated. PREG samples were characterized using 1D 1 H and 2D 1 H– 13 C HSQC NMR spectra. The qNMR assay method (taking approximately 10 min per NMR spectrum) was validated for precision, accuracy, specificity, robustness and linearity per ICH Q2(R1) guidance. The method was validated in a range from 0.032 to 3.2 mg/mL. As a proof of concept, seven PREG bulk substance samples, three tablet and two capsule PREG dietary supplements were assessed by the qNMR analytical procedure. NMR data from all tested samples met the expected criteria for identification and assay. The results demonstrate the potential of qNMR for the quality assessment of different types of PREG samples.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2022

CoSyR: A novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles’ radiation near-fields using wavefront/wavelet meshes via the Green’s function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. Here, the current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

Ballooning theory for micro-tearing mode in tokamak

This paper aims to investigate the impact of magnetic drift on the linear micro-tearing mode by using a kinetic approach to derive a reduced two-field eigen system in real space. Here, since the magnetic drift in real space has derivatives, it is more efficient to solve the mode equations in a Fourier-ballooning representation using the two-dimensional (2D) ballooning transform. The lowest-order eigen system in the Fourier-ballooning representation consists of two integral equations, which are numerically solved using the finite difference method for both eigenvalues and wave functions. The main results will be presented through graphical eigenvalue scans for each parameter. Furthermore, we present a graphical comparison between the predictions of the ballooning theory and GENE gyrokinetic code simulation in the pedestal region.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Exploring Nontrivial Topological Superconductivity in 2M-WS2 for Topological Quantum Computation

This project has two main research goals: (1) growing the high-quality two-dimensional (2D) 2M-pahse WS 2 (2M-WS 2 ) single crystals and identifying clear signatures of the unconventional superconductivity in the 2M-WS 2 ; and (2) establishing the layer-dependence of the Majorana zero mode in the 2M-WS 2 down to the monoatomic layer limit. These goals were planned to be achieved by growing high-quality and large-scale 2M-WS 2 single crystals and transferring their thin layers onto different substrates for the proposed measurements. The layer-dependent unconventional superconductivity in 2M-WS 2 were systematically studied by different techniques, including transport measurements (charge, thermal and spin), scanning tunneling microscopy and spectroscopy (STM/S), angle-resolved photoemission spectroscopy (ARPES), and theoretical calculations. The research team is comprised of researchers from University of Wyoming (UW) and three DOE National Laboratories (DOE NLs), including Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL) and Sandia National Laboratories (SNL), with complete and complementary expertise: PI Tian: Handling 2D materials, nanofabrication, nanodevices, and quantum transport; Co-Is: Ackerman and Leonard: van der Waals material crystal growth and handling; Chien: Nanoimaging with STM/S; and Tang: Magnetic measurements and charge and thermal transport; National lab collaborators (NLs): Guisinger (ANL): STM/S and nanoimaging; Mo and Rotenberg (LBNL): ARPES and nano ARPES (nARPES); Lu (SNL): Quantum information science, quantum transport, and nanofabrication; and Baczewski (SNL): Theoretical modeling and calculations.

36 MATERIALS SCIENCE↗

NASA NTRS1993

A time domain, weighted residual formulation of Maxwell's equations

A finite element model is developed and used to simulate two-dimensional electromagnetic wave propagation and scattering. The spatial discretization of the time-domain electrodynamic equations is accomplished by a Galerkin approach. The semi-discrete equations are solved explicitly using a second-order Runge-Kutta scheme. Both the electric and magnetic fields are discretized using a single grid, with the divergence-free conditions satisfied through a correction approach. Examples depicting the scattering of plane waves in 2D geometries are given to demonstrate the validity of the methodology.

Young, Jeffrey L.↗

DOE OSTI2021

Simulating Large PEPs Tensor Networks on Small Quantum Devices

We systematically map low bond dimension PEPs tensor networks to quantum circuits. By measuring and reusing qubits, we are in principle able to simulate an N×M square lattice PEPs network (for arbitrary M) of bond dimension 2 using N+ 2 qubits. We then seek to determine if this mapping can yield useful values for long-range loop observables in the presence of quantum device noise in the topological Wen plaquette model by mapping a 3×3 PEPs tensor network to a 5-qubit quantum circuit and executing it on the Honeywell System Model H1-1 trapped-ion device. We find that, for this system size, the noisy observable values are indeed sufficient for diagnosing topological vs. trivial order as the Wen model is perturbed by a magnetic field term in the Hamiltonian. We provide an overview of the experimental procedure and its results. We then explain in greater detail our method for mapping 2D tensor networks to quantum circuits and its scaling properties. This serves as a proof-of-concept of the utilty of the measure-and-reuse approach for simulating large 2D quantum systems on small quantum devices.

MacCormack, Ian↗

DOE OSTI2021

Experimental evidence that zinc impurities pin pair-density-wave order in La 2-x Ba x CuO 4

Both Zn doping and c-axis magnetic fields have been observed to increase the spin stripe order in La 2-x Ba x CuO 4 with x close to 1/8. For x = 0.095, the applied magnetic field also causes superconducting layers to decouple, presumably by favoring pair-density-wave order that consequently frustrates interlayer Josephson coupling. Here we show that introducing 1% Zn also leads to an initial onset of two-dimensional (2D) superconductivity, followed by 3D superconductivity at lower temperatures, even in zero field. Overall, we infer that the Zn pins pair-density-wave order locally, establishing the generality of such behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1993

Propagation characteristics of waves upstream and downstream of quasi-parallel shocks

The propagation characteristics of waves upstream and downstream of quasi-parallel shocks are investigated by using 2D hybrid simulations. At low Alfven Mach numbers, M(A) below about 2, the shock is initially associated with upstream phase-standing whistlers. At later times, backstreaming ions excite longer-wavelength whistlers via the right-hand resonant ion/ion instability. These waves propagate along the magnetic field at a group velocity no smaller than the upstream flow speed, so that the waves remain in the upstream region. At higher MA (above about 3), these waves are convected back into the shock, causing its reformation and downstream perturbations. Shock transmitted waves mode-convert into Alfven/ion-cyclotron waves which have a wave vector along the shock normal (pointing upstream) and convect downstream. The 2D simulation results confirm our earlier suggestion that the upstream waves should be field aligned, and that their convection into the downstream is associated with linear mode conversion into the Alfven/ion-cyclotron branch.

Krauss-Varban, D.↗