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DOE OSTI2024

Phase-field-guided design of record-high piezoelectricity and discovery of simultaneous high light transparency and high piezoelectricity in relaxor ferroelectrics

Here, the phase-field method has been extensively applied to predicting the domain structures and their responses to external fields and understanding experimentally observed domain states under different electromechanical conditions in ferroelectric heterostructures. This article highlights the successful examples of phase-field applications in guiding the design of relaxor ferroelectric ceramics and crystals with record-high piezoelectricity and the discovery of simultaneous high light transparency and piezoelectricity of relaxor ferroelectric crystals for a wide range of biomedical, robotics, and optoelectronics applications.

36 MATERIALS SCIENCE↗

DOE OSTI2023

A constitutive framework for rocks undergoing solid dissolution

Here, we formulate a time-dependent damage theory for rocks subjected to mechanical deformation and solid dissolution. The constitutive description is inspired by the transition state theory, which states that the rate of dissolution is a function of the reactive surface area measured through the crack density in the volume. We use a gradient-enhanced damage framework in which damage depends on the deformation of the material as well as on the amount of solid mass dissolved over time. The gradient-enhanced formulation is characterized by a three-field variational formulation with the solid displacement, nonlocal equivalent strain, and nonlocal rate of solid dissolution as the basic state variables. Traditionally, time-independent damage theories have only allowed damage to increase with increasing external load. In the proposed framework, the degree of damage may increase due to solid dissolution even when the external load is held fixed. In this way, solid dissolution is viewed as a process that is responsible for bringing about rate-dependent effects such as creep and stress-relaxation, which are two common features of geomaterial behavior.

42 ENGINEERING↗

DOE OSTI2025

Spin Seebeck effect in correlated antiferromagnetic V 2 ⁢O 3

The spin Seebeck effect is useful for probing the spin correlations and magnetic order in magnetic insulators. Here, we report a strong local spin Seebeck effect (LSSE) in antiferromagnetic V 2 ⁢O 3 thin films. The LSSE response at cryogenic temperatures increases as a function of the external magnetic field until it approaches saturation. The response at a given power and field exhibits a nonmonotonic temperature dependence, with a pronounced peak that shifts toward higher temperatures as the field increases. Furthermore, the magnitude of the LSSE signal decreases consistently with increasing thickness, implying that the bulk SSE dominates any interfacial contribution. Here, this negative correlation between the SSE and the thickness implies that the magnon energy relaxation length in V 2 ⁢O 3 is shorter than the thickness of our thinnest film, 50 nm, consistent with the strong spin-lattice coupling in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Electrodynamics of Thin Sheets of Twisted Material

We construct a minimal theory describing the optical activity of a thin sheet of a twisted material, the simplest example of which is twisted bilayer graphene. We introduce the notion of "twisted electrical conductivity", which parametrizes the parity-odd response of a thin film to a perpendicularly falling electromagnetic waves with wavelength larger than the thickness of the sheet. Here, we show that the low-frequency Faraday rotation angle has different behaviors in different phases. For an insulator, the Faraday angle behaves as ω 2 at low frequencies, with the coefficient being determined by the linear relationship between a component of the electric quadrupole moment and the external electric field. For superconductors, the Faraday rotation angle is constant when the frequency of the incoming EM waves is below the superconducting gap and is determined by the coefficient of the Lifshitz invariant in the Ginzburg-Landau functional describing the superconducting state. In the metallic state, we show that the twisted conductivity is proportional to the "magnetic helicity" (scalar product of the velocity and the magnetic moment) of the quasiparticle, averaged around the Fermi surface. The theory is general and is applicable to strongly correlated phases.

Son, Dam Thanh↗

DOE OSTI2021

Dynamic Interconversion of Metal Active Site Ensembles in Zeolite Catalysis

Catalysis science is founded on understanding the structure, number, and reactivity of active sites. Kinetic models that consider active sites to be static and noninteracting entities are routinely successful in describing the behavior of heterogeneous catalysts. Yet, active site ensembles often restructure in response to their external environment and even during steady-state catalytic turnover, sometimes requiring non-mean-field kinetic treatments to describe distance-dependent interactions among sites. Such behavior is being recognized more frequently in modern catalysis research, with the advent of experimental methods to quantify turnover rates with increasing precision, an expanding arsenal of operando characterization tools, and computational descriptions of atomic structure and motion at chemical potentials and timescales increasingly relevant to reaction conditions. This review focuses on dynamic changes to metal active site ensembles on zeolite supports, which are silica-based crystalline materials substituted with Al that generate binding sites for isolated and low-nuclearity metal site ensembles. Metal sites can become solvated and mobilized during reaction, facilitating interactions among sites that change their nuclearity and function. Such intersite communication can be regulated by the zeolite support, resulting in non-single-site and potentially non-mean-field kinetic behavior arising from mechanisms of catalytic action that combine elements of those canonically associated with homogeneous and heterogeneous catalysis. Here, we discuss recent literature examples that document dynamic active site behavior in metal-zeolites and outline methodologies to identify and interpret such behavior. We conclude with our outlook on future research directions to develop this evolving branch of catalysis science and harness it for practical applications.

operando characterization↗

DOE OSTI2020

A spin-wave magnetometer with a positive feedback

In this work, we demonstrate experimentally the operation of a spin-wave magnetometer integrated into a circuit with a positive feedback. The circuit consists of the passive magnetic and active electric parts. The magnetic part includes a sensing element, which is a magnetic cross junction made of Y 3 Fe 2 (FeO 4 ) 3 . The electric part includes a non-linear amplifier and a phase shifter. The electric and magnetic parts are connected via micrometer size antennae. Spin waves are excited by two of these antennae while the output inductive voltage produced by the interfering spin waves is detected by the third antenna. Spin waves propagating in the orthogonal arms of the cross can accumulate significantly different phase shifts, depending on the direction and the strength of the external magnetic field. The output inductive voltage reaches its maximum in the case of constructive spin wave interference. The positive feedback provides further signal amplification. It appears possible to enhance the response function, compared to the passive circuits without a feedback, by a factor of ×100 without an increase in the noise level. The experimental data show a prominent response to the external magnetic field variation, exceeding 5 x 10 3 V/T. The intrinsic noise spectral density of the device can be as low as 10 -16 V 2 /Hz. The estimated sensitivity of the prototype device is 2 x 10 -12 T/√Hz at room temperature. We argue that spin-wave magnetometers can potentially be as sensitive as SQUIDs while operating at room temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Experimental study of electromagnetic wave scattering from a gyrotropic gaseous plasma column

We experimentally demonstrate the controlled scattering of incident transverse-electric electromagnetic waves from a gyrotropic magnetized plasma cylindrical discharge. Scattered electromagnetic waves can bend left and right by changing the external magnetic field of a plasma rod. Measured scattered wavefronts are in good agreement with electromagnetic simulations. A gyrotropic response is observed for incident wave frequencies ranging from 3.5 to 5.6 GHz for conditions corresponding to a ratio of cyclotron frequency to plasma frequency, ω ce /ω p ≈ 0.16. In conclusion, the observation of a gyrotropic response from cylindrical plasma discharges paves the way for their use as building blocks for future devices such as magnetized plasma photonic crystals, topological insulators, plasma metamaterials, non-reciprocal waveguide structures, and other devices, which require a tunable gyrotropic response from centimeter to meter-scale materials with application-specific geometry.

42 ENGINEERING↗

DOE OSTI2020

Topological orders of monopoles and hedgehogs: From electronic and magnetic spin-orbit coupling to quarks

Topological states of matter are, generally, quantum liquids of conserved topological defects. We establish this by constructing and analyzing topological field theories which introduce gauge fields to describe the dynamics of singularities in the original field configurations. In this work, homotopy groups are utilized to identify topologically protected singularities, and the conservation of their protected number is captured by a topological action term that unambiguously obtains from the given set of symmetries. Stable phases of these theories include quantum liquids with emergent massless Abelian and non-Abelian gauge fields, as well as topological orders with long-range quantum entanglement, fractional excitations, boundary modes, and unconventional responses to external perturbations. This paper focuses on the derivation of topological field theories and basic phenomenological characterization of topological orders associated with homotopy groups π n (S n ), n ≥ 1 . These homotopies govern monopole and hedgehog topological defects in d = n + 1 dimensions, and enable the generalization of both weakly interacting and fractional quantum Hall liquids of vortices to d > 2 . Hedgehogs have not been in the spotlight so far, but they are particularly important defects of magnetic moments because they can be stimulated in realistic systems with spin-orbit coupling, such as chiral magnets and d = 3 topological materials. We predict topological orders in systems with U(1) × Spin(d) symmetry in which fractional electric charge attaches to hedgehogs. Monopoles, the analogous defects of charge or generic U(1) currents, may bind to hedgehogs via Zeeman effect, or effectively emerge in purely magnetic systems. The latter can lead to spin liquids with different topological orders than that of the resonant valence bond spin liquid. Charge fractionalization of quarks in atomic nuclei is also seen as possibly arising from the charge-hedgehog attachment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

A Fast Mechanical Tuner for SRF Cavities

There is a particular need for fast tuners and phase shifters for advanced superconducting accelerator RF systems. The tuners based on ferrite, ferroelectric and piezo materials are commonly used. However, those methods suffer from one or another issue of high power loss, slow response, and narrow tuning range. We propose a robust, fast (up to ~5 MHz/sec), high efficient mechanical tuner for SRF cavities operating at the frequency 50 MHz. We develop an external mechanical tuner that is strongly coupled to the cavity. The tuner design represents a trade-off of high efficiency (low RF losses and low heat flux) and frequency tunability range. Our approach solves this trade-off issue. We propose RF design which exploits two coupled resonators so that a main high-field cavity is controlled with a small tunable resonator with a flexible metallic wall operating in a relatively low RF field. Simulations, carried out for a 7.5 MV/m 50 MHz SRF Quarter Wave Resonator (QWR), show that frequency tunability at level 10⁻³ is obtainable.

43 PARTICLE ACCELERATORS↗

NASA NTRS2007

A Method to have Multi-Layer Thermal Insulation Provide Damage Detection

Design and testing of a multi-layer thermal insulation system that also provides debris and micrometeorite damage detection is presented. One layer of the insulation is designed as an array of passive open-circuit electrically conductive spiral trace sensors. The sensors are a new class of sensors that are electrically open-circuits that have no electrical connections thereby eliminating one cause of failure to circuits. The sensors are powered using external oscillating magnetic fields. Once electrically active, they produce their own harmonic magnetic fields. The responding field frequency changes if any sensor is damaged. When the sensors are used together in close proximity, the inductive coupling between sensors provides a means of telemetry. The spiral trace design using reflective electrically conductive material provides sufficient area coverage for the sensor array to serves as a layer of thermal insulation. The other insulation layers are designed to allow the sensor s magnetic field to permeate the insulation layers while having total reflective surface area to reduce thermal energy transfer. Results of characterizing individual sensors and the sensor array s response to punctures are presented. Results of hypervelocity impact testing using projectiles of 1-3.6 millimeter diameter having speeds ranging from 6.7-7.1 kilometers per second are also presented.

Woodward, Stanley E.↗

DOE OSTI2024

Supramolecular Metal Halide Complexes for High-Temperature Nonlinear Optical Switches

Nonlinear optical (NLO) switching materials, which exhibit reversible intensity modulation in response to thermal stimuli, have found extensive applications across diverse fields, including sensing, photoelectronics, and photonic applications. While significant progress has been made in solid-state NLO switching materials, these materials typically showcase their highest NLO performance near room temperature. However, this performance drastically deteriorates upon heating, primarily due to the phase transition undergone by the materials from non-centrosymmetric to centrosymmetric phase. Here, we introduce a new class of NLO switching materials, solid-state supramolecular compounds 18-Crown-6 ether@Cu 2 Cl 4 ·4H 2 O (1·4H 2 O), exhibiting reversible and stable NLO switching when subjected to near-infrared (NIR) photoexcitation and/or thermal stimuli. The reversible crystal structure in response to external stimuli is attributed to the presence of a weakly coordinated bridging water molecule, facilitated by hydrogen bonding/chelation interactions between the metal halide and crown-ether supramolecules. We observed an exceptionally high second-harmonic generation (SHG) signal under continuous photoexcitation, even at temperatures exceeding 110°C. In addition, the bridging water molecules within the complex can be released and recaptured in a fully reversible manner, all without requiring excessive energy input. This feature allows for precise control of SHG signal activation and deactivation through structural transformations, resulting in a high-contrast off/on ratio, reaching values in the million-fold range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Stimulus-Responsive Modulation of Solvation Environments in Solid Catalysts

Liquid environments play a crucial role in the biological processes occurring in living organisms as well as in many human-made processes involving electrochemistry, photo-, and thermocatalysis. In the majority of these systems, aqueous phases are ubiquitous due to water’s natural abundance. Water molecules, however, can exert large changes in the chemical environment of catalytically active sites, altering the reaction rates, selectivity, and catalyst stability. These solvation effects induced by water molecules near catalytic sites can drastically change the energy landscape and unlock unique reaction pathways with far more favorable kinetics. In nature, living organisms couple these complex interactions with detection, communication, and actuation mechanisms to induce self-regulatory behavior, ensuring stability of the system and thus long-term durability. Extrapolating this behavior to heterogeneous catalysis is desirable because the resulting “smart materials” can potentially unlock new chemical conversion processes with higher atom efficiency, rates, and stability. The combination of polymer chemistry and heterogeneous catalysis has introduced versatile approaches for creating materials that can respond to cues in the reaction medium that alter the accessibility, intrinsic activity, and selectivity of the catalyst. To achieve this, one could combine stimulus-responsive polymers, which undergo a large volumetric phase transition in response to an external stimulus, with a solid catalyst. This chemo-mechanical response has been employed to create a variety of nanoreactor vessels with stimulus-responsive character that turn on- and off- depending on the reaction conditions. In this Account, we focus on the impact of these polymer coatings on the solvation environment around the active site and the implications of these effects on the reaction energy landscape, molecular arrangement of the solvent, electric fields at the catalyst–liquid interface, binding energy, and mobility of surface reaction intermediates. These seemingly subtle changes in solvent molecules induced by the presence of polymers can have a tremendous impact on the development of bioinspired heterogeneous catalysts, reliable chemical clocks, micro/nanoreactors, and robots. The large library of polymer chemistries offers a plethora of combinations of stimulus-responsive mechanisms (e.g., temperature, pH, light, magnetic field, solvent composition), providing the possibility of creating homeostatic catalysts à la carte.

catalysts↗

DOE OSTI2024

Quantum Hall effect in a Weyl-Hubbard model: Interplay between topology and correlation

The interplay between topology and electronic correlations offer a rich avenue for discovering emergent quantum phenomena in condensed matter systems. Here, in this work, starting from the Weyl-Hubbard model, we investigate the quantum Hall effect to explore the consequence of onsite Hubbard repulsion on nontrivial Weyl band topology in the presence of an external magnetic field. Within the Gutzwiller projected wavefunction method, we find the system to undergo multiple topological phase transitions by tuning on-site Coulomb interaction, including two distinct Weyl phases with different numbers of Weyl node pairs and a trivial narrow band insulator. Crucially, these two Weyl phases may be identified by the sign of their chiral Landau levels. The possible experimental signature of these topological phases and correlation effects is provided by the magnetic-field dependent quantum Hall conductivity within the Kubo response theory.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Organismic materials for beyond von Neumann machines

The elementary basis of intelligence in organisms with a central nervous system includes neurons and synapses and their complex interconnections forming neural circuits. In non-neural organisms such as slime mold with gel-like media, viscosity modulation enables adaptation to changing environments. At a larger scale, collective intelligence emerges via social interactions and feedback in animal colonies. Learning and memory are therefore multi-scale features that evolve as a result of constant interactions with the environment. There is growing interest in emulating such features of intelligence in computing machines and autonomous systems. Materials that can respond to their environment in a manner similar to organisms (referred to as "organismic materials") therefore may be of interest as hardware components in artificial intelligence machines. In this brief review, we present a class of semiconductors called correlated oxides as candidates for learning machines. The term "correlated" refers to the fact that electrons in such lattices strongly interact and the ground state is not what is predicted by classical band theory. Such materials can undergo insulator-metal transitions at near ambient conditions under external stimuli such as thermal or electrical fields, strain, and chemical doping. Depending on the mechanism driving the transition, intermediate states can be metastable with different volatilities, and the time scales of phase change can be controlled over many orders of magnitude. The change in electronic properties can be sharp or gradual, leading to digital or analog behavior. These properties enable the realization of artificial neurons and synapses and emulate the associative and non-associative learning characteristics found in various organisms. We examine microscopic properties concerning electronic and structural transitions leading to collective behavior and theoretical treatments of the ground state and dynamical response, showcasing VO 2 as a model system. Next, we briefly review algorithms designed from the plasticity demonstrated by phase changing systems. Finally, we conclude the brief review with suggestions for future research toward realizing non-von Neumann machines.

42 ENGINEERING↗

DOE OSTI2025

Searching for Phase Transitions in Artificial Kagome Spin Ice

Artificial Kagome spin ice is a metasurface consisting of small islands of polarizable magnets. These islands can be oriented by an external magnetic field applied in the same plane as the metasurface. By subsequently applying a relatively weaker field in the opposite direction of the initial field, a portion of the magnets in the lattice can be repolarized or “flipped” the other way. These flips cause instabilities in a previously uniformly aligned lattice, causing the system to interact with itself and induce changes in the overall magnetization of the metasurface. This Summer, my goal was to use this phenomenon to discern whether or not these systems could undergo a phase transition caused only by the initial change of the external magnetic field. Based on previous datasets that indicated that such a transition was observable, my task was to find and reproduce this potential phenomena. This process was conducted by repeating measurements on the system by using an external magnet to align the spin ice and then using Magnetic Force Microscopy (MFM) to probe the surface of the material to understand the changes in the magnetization over time. This report will discuss the characteristics of artificial Kagome spin ice, the methodology used to induce phase transitions, and the image processing methods used to understand the results. Although no reproducible evidence of a phase transition was found during the Summer, we were able to successfully reproduce short-term responses in the spin ice, as well as plot a hysteresis curve of the material.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2026

Analytic Nuclear Gradients Including Oriented External Electric Fields in a Molecule-Fixed Frame

Electric-field-assisted chemistry has attracted much attention in recent years, particularly in the context of oriented external electric fields for controlling molecular structure and reactivity. Such fields have been explored in a wide range of applications, including switching materials, nanoparticles, controllable catalysts, medicines, and clinical therapies. However, the determination of fixed fields in the laboratory frame becomes ineffective for flexible molecules, as conformational changes can significantly alter the relative orientation between the applied field and molecular structure. In this work, we propose two molecular reference frames─the principal axis frame and the local reference frame─to define oriented electric fields within the molecular framework. These coordinate systems powerfully eliminate ambiguities in the relative orientation between the applied field and the molecule. Analytic nuclear gradients in the presence of external electric fields are derived and implemented, with an initial application to field-dependent geometry optimizations of cis - and trans -formanilide. Analysis of the resulting field-induced equilibrium structures reveals distinct structural responses, validating the accuracy and robustness of the proposed formalism. The analytic gradient framework enables systematic investigations of molecular properties and reactivity under arbitrarily oriented electric fields, opening new opportunities for computational modeling and rational design in electric-field-controlled chemistry.

electric fields↗

DOE OSTI2021

Specialized diamond materials for NMR applications

Polarizable diamond materials and methods for obtaining nuclear magnetic resonance spectra of samples external to the diamond materials are described. The diamond materials can include 12C, 13C, substitutional nitrogen, and nitrogen vacancy defects in a crystalline lattice, wherein the substitutional nitrogen concentration is between 10 ppm and 200 ppm, the nitrogen vacancy concentration is between 10 ppb and 10 ppm, and the 13C concentration is greater than 1.1% and not more than 25%. Methods for obtaining nuclear magnetic resonance spectra can include optically pumping a diamond material to generate electron spin hyperpolarization in nitrogen vacancy centers, transferring the electron spin hyperpolarization to nuclei of the sample, and generating a nuclear magnetic resonance spectrum by applying a magnetic field to the sample, exciting the sample with a radio frequency pulse, and detecting a nuclear magnetic resonance response from the sample.

Parker, Alfred↗

DOE OSTI2022

Magnetic ground states of a model for M Nb 3 S 6 ( M = Co, Fe, Ni)

The transition-metal-intercalated dichalcogenide CoNb 3 S 6 is a triangular antiferromagnet (AFM) that has recently been shown to exhibit a large anomalous Hall effect (AHE) below the Neel temperature, even though the response to an external field is very small. This suggests that there is an interesting magnetic structure that interacts with the electronic structure to yield the AHE, as collinear AFMs cannot exhibit a nonzero AHE. We propose a model for magnetic transition-metal-intercalated dichalcogenides and examine its ground state as a function of interaction parameters. The model exhibits transitions between planar spin spirals, nonplanar spin spirals, and a particular noncoplanar so-called 3q state. Finally, this latter state must exhibit a nonzero AHE, while the spin spirals do not.

36 MATERIALS SCIENCE↗