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All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Miniaturized Airborne Imaging Central Server System

In recent years, some remote-sensing applications require advanced airborne multi-sensor systems to provide high performance reflective and emissive spectral imaging measurement rapidly over large areas. The key or unique problem of characteristics is associated with a black box back-end system that operates a suite of cutting-edge imaging sensors to collect simultaneously the high throughput reflective and emissive spectral imaging data with precision georeference. This back-end system needs to be portable, easy-to-use, and reliable with advanced onboard processing. The innovation of the black box backend is a miniaturized airborne imaging central server system (MAICSS). MAICSS integrates a complex embedded system of systems with dedicated power and signal electronic circuits inside to serve a suite of configurable cutting-edge electro- optical (EO), long-wave infrared (LWIR), and medium-wave infrared (MWIR) cameras, a hyperspectral imaging scanner, and a GPS and inertial measurement unit (IMU) for atmospheric and surface remote sensing. Its compatible sensor packages include NASA s 1,024 1,024 pixel LWIR quantum well infrared photodetector (QWIP) imager; a 60.5 megapixel BuckEye EO camera; and a fast (e.g. 200+ scanlines/s) and wide swath-width (e.g., 1,920+ pixels) CCD/InGaAs imager-based visible/near infrared reflectance (VNIR) and shortwave infrared (SWIR) imaging spectrometer. MAICSS records continuous precision georeferenced and time-tagged multisensor throughputs to mass storage devices at a high aggregate rate, typically 60 MB/s for its LWIR/EO payload. MAICSS is a complete stand-alone imaging server instrument with an easy-to-use software package for either autonomous data collection or interactive airborne operation. Advanced multisensor data acquisition and onboard processing software features have been implemented for MAICSS. With the onboard processing for real time image development, correction, histogram-equalization, compression, georeference, and data organization, fast aerial imaging applications, including the real time LWIR image mosaic for Google Earth, have been realized for NASA fs LWIR QWIP instrument. MAICSS is a significant improvement and miniaturization of current multisensor technologies. Structurally, it has a complete modular and solid-state design. Without rotating hard drives and other moving parts, it is operational at high altitudes and survivable in high-vibration environments. It is assembled from a suite of miniaturized, precision-machined, standardized, and stackable interchangeable embedded instrument modules. These stackable modules can be bolted together with the interconnection wires inside for the maximal simplicity and portability. Multiple modules are electronically interconnected as stacked. Alternatively, these dedicated modules can be flexibly distributed to fit the space constraints of a flying vehicle. As a flexibly configurable system, MAICSS can be tailored to interface a variety of multisensor packages. For example, with a 1,024x1,024 pixel LWIR and a 8,984x6,732 pixel EO payload, the complete MAICSS volume is approximately 7x9x11 in. (=18x23x28 cm), with a weight of 25 lb (=11.4 kg).

Sun, Xiuhong↗
DOE OSTI2026

Pressure-Stabilized MnSb2 with Complex Incommensurate Magnetic Order

Marcasite-type compounds have been proposed as promising hosts of exotic magnetic quantum states, yet experimental realizations in stoichiometric, disorder-free systems remain limited. Here, we report the high-pressure stabilization and magnetic characterization of MnSb2, a marcasite-type compound that is thermodynamically metastable under ambient pressure. Single crystals were synthesized using a cubic multianvil press at 3.3 GPa and 490 °C for 24 h, and powder and single-crystal X-ray diffraction confirm the orthorhombic Pnnm structure. These crystals are stable at ambient pressure for a long time up to between 450 and 500 K. Heat-capacity measurements reveal phase transitions at approximately T0 ∼ 118 K and T1 ∼ 220 K. Neutron diffraction uncovers an unconventional magnetic state below T1 ∼ 220 K. Magnetic powder neutron diffraction refinements reveal possible multiple magnetic configurations that provide comparably acceptable fits to the experimental data. While most solutions are consistent with a spin-density-wave (SDW) description, helical models systematically yield inferior agreement factors. Across a broad range of models, the Mn ordered moment reaches a maximum value of approximately 2 μB and remains predominantly collinear, with minimal canting along the c-axis. At 200 K, the magnetic propagation vector is q = (0, 0.3975, 0.3783); upon cooling, the b component increases toward 0.5, reflecting a temperature-dependent evolution of the modulation. The need for modification of the magnetic model between high and low temperatures further highlights the complex and strongly temperature-dependent nature of the magnetic order in this system. These results establish MnSb2 as a pressure-stabilized marcasite magnet with a tunable, complex magnetic state and a compelling stoichiometric platform for exploring unconventional magnetic behavior, including potential altermagnetism.

Xu, Mingyu [Michigan State University , , , ,; Iow↗
DOE OSTI2026

Metal-Dependent Photodissociation of Hydrazone Photoswitches from Rare-Earth Complexes

Rare-earth element separation processes often rely on a small decrease in ionic radii along the series of elements. Separation processes based on the distinct optical properties of REs remain less explored, although photochemical methods may offer a viable alternative. Accurate selection of the synthetic precursors of a photoswitchable acylhydrazonic ligand led to a system that could quantitatively isomerize (E−to−Z) upon irradiation with commercial LED lights. Coordination of the photoswitch with RE III nitrates (RE = La−Lu except Pm and Y) resulted in the retention of the photoswitching properties observed in solution. The lower binding affinity of the generated Z−isomer with RE III ions yielded the dissociation of the complexes upon irradiation (photodissociation) with the release of RE−nitrates in solution. The rate of the reaction was found to be dependent on the optical properties of the RE III ions, with nonemissive complexes (no 4f excited states) dissociating faster than emissive ones (having accessible 4f excited states). A thorough solid-state characterization of the complexes was performed by using crystallographic and photochemical methods. Ultimately, the accessibility of the 4f excited states of the metals following light irradiation and excitation of the ligand led to a decrease in the rate of the reaction due to quenching of the ligand excited state. These results demonstrate that the direct modulation of the metal coordination environment, combined with the metal-dependent reaction rate, could provide a strategy for the development of RE−separation processes based on differences in their optical properties.

Ions↗
DOE OSTI2023

THz Plasmonics and Topological Optics of Weyl Semimetals

THz magneto-optical properties of 3D topological Weyl semimetals were investigated with both THz spectroscopy and THz pump-probe measurements. The unique THz effects predicted in these materials may have important applications in THz technology. The electronic band structure was characterized spectroscopically through THz zero-field reflectance and/or cyclotron resonance measurements. The studies included the dynamic chiral pumping and the study of the predicted novel magneto-electric effects arising from the underlying Berry curvature and magneto plasmonic-like effects in the absence of an applied magnetic field. Chiral pumping in the extreme quantum limit was studied on Weyl semimetals to directly probe the chiral N=0 Landau level. Non-linear pump-probe measurements were used to measure the chiral pumping lifetime. Solids with topologically robust electronic states exhibit unusual electronic and optical transport properties that do not exist in other materials. A particularly interesting example is chiral charge pumping, the so-called chiral anomaly, in recently discovered topological Weyl and Dirac semimetals, where simultaneous application of parallel DC electric and magnetic fields creates an imbalance in the number of carriers of opposite topological charge (chirality). In an earlier study we investigated the Weyl metals Na 3 Bi and Cd 3 As 2 . In this grant we followed up with magneto-optical studies of TaAs, another Weyl semimetal. More recently, we have also characterized other Weyl and Dirac systems that have come on line. The Physics community is still looking for the “hydrogen atom” of the Weyl semimetal. CoSi is one promising new system which features Weyl node spacing comparable to the Brillouin zone size. This system may be suitable for study of the predicted chiral plasmons that arise from the Berry curvature in Weyl materials. In other experiments gates can be applied to the samples in order to study the Fermi arc surface states by modulation reflectance spectroscopy at THz frequencies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Exploring Excited State Proton Transfer Dynamics upon Ultraviolet Excitation

Excited state intramolecular proton transfer (ESIPT) has been investigated in two prototypical systems─salicylaldehyde azine (SAA) and 1,5-dihydroxyanthraquinone (DHAQ)─using transient absorption spectroscopy upon ultraviolet excitation into the less studied higher excited (S n ) manifold. Excitation with sub-30 fs pulses and broadband visible probing has allowed for direct measurement of the ESIPT rate. In conjunction with steady-state measurements and TD-DFT calculations, a complete delineation of the ultrafast photophysics has been carried out. In SAA, ESIPT remains ultrafast (∼30 fs), consistent with previous S 1 excitation studies. Coherent vibrational beats maps reveal significant wavelength dependence, however. Theoretical analysis suggests that the observed modes and their intensities in coherent vibrational spectra are modulated by the nature of the electronically excited state. In DHAQ, the first direct observation of ESIPT presents a time-constant of ∼85 fs, and a slower component of 9 ps, akin to previous reports on double-proton transfer systems. Collectively, the results suggest that while the ultrafast ESIPT rate remains largely invariant vis-à-vis the excitation energy, the product yield, as well as accompanying coherent oscillations, may be substantively altered, owing to the existence of alternative decay pathways.

excited states↗
DOE OSTI2020

Phasing of seven-channel fibre laser radiation with dynamic turbulent phase distortions using a stochastic parallel gradient algorithm at a bandwidth of 450 kHz

We have demonstrated an experimental setup for the coherent phasing of a seven-channel fibre laser system ( λ = 1064 nm) in a scheme comprising a master oscillator and a set of parallel amplifiers with lithium niobate-based fibre-optic phase modulators. Using a stochastic parallel gradient algorithm, an instrumental phase modulator control unit ensures a bandwidth of the system up to 450 kHz. The effectiveness of phasing of light transmitted through a turbulent medium with a characteristic time scale τ{sub turb} has been studied experimentally as a function of phasing time τ{sub ph}. The results demonstrate that the average Strehl ratio begins to rise at τ{sub turb}/τ{sub ph} ⩾ 2 and that the effectiveness of compensation for dynamic phase distortions in the beam propagation path rises sharply at τ{sub turb}/τ{sub ph} ≈ 20. For τ{sub turb}/τ{sub ph} ⩾ 30 – 40, the average Strehl ratio remains constant at the level reached. (control of laser radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Gate-Tunable Proximity Effects in Graphene on Layered Magnetic Insulators

The extreme versatility of van der Waals materials derives from their ability to exhibit new electronic properties when assembled in proximity with dissimilar crystals. 1 For example, although graphene is inherently non-magnetic, recent work has reported a magnetic proximity effect in graphene interfaced with magnetic substrates, potentially enabling a pathway towards achieving a high-temperature quantum anomalous Hall effect. Here, we investigate heterostructures of graphene and chromium trihalide magnetic insulators (CrI 3 , CrBr 3 , and CrCl 3 ). Surprisingly, we are unable to detect a magnetic exchange field in the graphene, but instead discover proximity effects featuring unprecedented gate-tunability. The graphene becomes highly hole-doped due to charge transfer from the neighboring magnetic insulator, and further exhibits a variety of atypical gate-dependent transport features. The charge transfer can additionally be altered upon switching the magnetic states of the nearest CrI 3 layers. In conclusion, our results provide a roadmap for exploiting proximity effects arising in graphene coupled to magnetic insulators.

2D magnet↗
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 OSTI2022

Active Cancellation of Servo-Induced Noise on Stabilized Lasers via Feedforward

Many precision laser applications require active frequency stabilization. However, such stabilization loops operate by pushing noise to frequencies outside their bandwidth, leading to large “servo bumps” that can have deleterious effects for certain applications. The prevailing approach to filtering this noise is to pass the laser through a high-finesse optical cavity, which places constraints on the system design. Here, we propose and demonstrate a different approach where a frequency error signal is derived from a beat note between the laser and the light that passes through the reference cavity. The phase noise derived from this beat note is fed forward to an electro-optic modulator after the laser, carefully accounting for relative delay, for real-time frequency correction. With a hertz-line-width laser, we show ≳20 dB noise suppression at the peak of the servo bump (approximately 250 kHz) and a noise-suppression bandwidth of approximately 5 MHz—well beyond the servo bump. By simulating the Rabi dynamics of a two-level atom with our measured data, we demonstrate substantial improvements to the pulse fidelity over a wide range of Rabi frequencies. Here, our approach offers a simple and versatile method for obtaining a clean spectrum of a narrow-line-width laser, as required in many emerging applications of cold atoms, and is readily compatible with commercial systems that may even include wavelength conversion.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Corrosion of novel reactive silver ink and commercial silver-based metallizations in diluted acetic acid

Silver-based metallizations in photovoltaic modules are susceptible to corrosion by acetic acid generated in ethylene vinyl acetate encapsulated modules, resulting in power losses over time. Here, three silver-based metallizations are exposed to diluted acetic acid, in concentrations representative of that found in field-exposed modules. Compositional, morphological, and structural changes of the metallizations are studied over 3000 h of exposure to diluted acetic acid using Raman spectroscopy mapping, X-ray diffraction, and scanning electron microscopy. The three metallizations studied are: 1) a commercial high-temperature fire-through Ag paste, commonly used for Si diffused junction solar cells; 2) a commercial low-temperature paste normally used for silicon heterojunction cells; and 3) a novel low-temperature reactive silver ink shown to be suitable for photovoltaic applications. We find distinct corrosion rates for the high-temperature silver paste and reactive silver ink in the presence of diluted acetic acid. However, the low-temperature silver paste appears to be more corrosion resistant, likely due to a polymer layer that protects the silver particles.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Search for Magnetic Accretion in SW Sextantis Systems

SW Sextantis systems are nova-like cataclysmic variables that have unusual spectroscopic properties, which are thought to be caused by an accretion geometry having part of the mass flux trajectory out of the orbital plane. Accretion onto a magnetic white dwarf is one of the proposed scenarios for these systems. To verify this possibility, we analyzed photometric and polarimetric time-series data for a sample of six SW Sex stars. We report possible modulated circular polarization in BO Cet, SW Sex, and UU Aqr with periods of 11.1, 41.2, and 25.7 minutes, respectively, and less significant periodicities for V380 Oph at 22 minutes and V442 Oph at 19.4 minutes. We confirm previous results that LS Peg shows variable circular polarization. However, we determine a period of 18.8 minutes, which is different from the earlier reported value. We interpret these periods as the spin periods of the white dwarfs. Our polarimetric results indicate that 15% of the SW Sex systems have direct evidence of magnetic accretion. We also discuss SW Sex objects within the perspective of being magnetic systems, considering the latest findings about the demography, formation, and evolution of cataclysmic variables.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRSDate not supplied

Initial Test Results for NASA Goddard’s Low-Cost Optical Terminal Adaptive Optics System

This presentation presents the testing approach and initial laboratory test results of the Adaptive Optics (AO) Subassembly (AOS) for the Low-Cost Optical Terminal (LCOT), a low-cost and flexible optical communications ground terminal. Leveraging commercial components and subassemblies wherever possible, LCOT is being developed by the NASA Goddard Space Flight Center (GSFC) Advanced Communications Capabilities for Exploration and Science Systems (ACCESS) project. An economical ground terminal allows NASA to create a global optical terminal network and enables the expansion of direct-to-Earth (DTE) optical communications. Located at the Goddard Geophysical and Astronomical Observatory (GGAO), LCOT is in the development phase and will receive first light during initial testing beginning in 2023. This new optical terminal includes a 700 mm Ritchey-Chretien commercial telescope, able to track Low Earth Orbit (LEO) spacecraft, receive instruments specified from 1500 - 1600 nm, and an uplink transmit optical system. Demodulation of optical coherent modulation formats requires downlink signal coupling into single-mode fiber. Due to atmospheric turbulence, signals experience wavefront distortions creating speckle patterns larger than the fiber core and high jitter requiring precise beam steering. AO is necessary to correct atmospheric turbulence effects and allow efficient coupling of received signals. In 2020, GSFC contracted with General Atomics to provide the LCOT AO system. This system has been delivered to GSFC in September 2021 and has been tested in laboratory to evaluate performance. This paper describes the laboratory testing approach, turbulence phase plate design, test results, and the AO field testing plan when installed on the LCOT telescope.

Adaptive Optics↗
NASA NTRS2004

Sensor for Monitoring Nanodevice-Fabrication Plasmas

The term plasma process diagnostics (PPD) refers to a spectroscopic technique and sensing hardware that have been proposed for monitoring plasma processes used to fabricate electronic devices that feature sizes as small as several nanometers. Nanometer dimensions are characteristic of the quantum level of miniaturization, where single impurity atoms or molecules can drastically change the local properties of the nanostructures. Such changes may be purposely used in nanoscale design but may also be extremely damaging or cause improper operation of the fabricated devices. Determination of temperature and densities of reactants near the developing features is important, since the structural synthesis is affected by characteristics of the local microenvironment. Consequently, sensors capable of nonintrusive monitoring with high sensitivity and high resolution are essential for real-time atomistic control of reaction kinetics and minimizing trace contamination in plasma processes used to fabricate electronic nanodevices. Such process-monitoring sensors are required to be compact, multiparametric, and immune to the harsh environments of processing plasmas. PPD is intended to satisfy these requirements. The specific technique used to implement plasma diagnostics with a PPD sensor would be an advanced version of continuous-wave cavity-ringdown spectroscopy (CW-CRDS) capable of profiling spectral line broadenings in order to derive both Doppler and Stark components. CRDS is based on measurements of the rate of absorption of laser light in an optical resonator. The ultimate sensitivity results from a very long absorption path length within the cavity and immunity to variations in incident laser intensity. The proposed version of this technique would involve the use of multiplexing tunable laser diodes and an actively modulated high-reflectivity optical resonator, thus offering a synergistic combination of simplicity, compactness, high sensitivity, and high resolution. The multiplexing capabilities of diode lasers could be utilized to make the PPD sensor a single, simple, compact, and inexpensive tool for the acquisition of multiparametric data. A PPD sensor would be capable of continuous measurement of such physical parameters as gas temperature, gas velocity, electron number density, and absolute densities of reacting chemical species. A laser beam can be easily adjusted to analyze the immediate vicinity of the growing nanostructures (or features etched down) in real time. The absorption enhancement in an optical cavity would afford the sensitivity needed for measurement of the temperature and densities of species at concentrations significantly lower than measurable by other nonintrusive techniques. It is anticipated that fully developed PPD sensors would enable simultaneous measurement of local temperature and determination of plasma species responsible for the synthesis and functionalization of nanodevices. These sensors would also enable tracking the pathways and origins of damaging contaminants, thereby providing feedback for adjustment of processes to optimize them and reduce contamination. The PPD sensors should also be useful for optimization of conventional microelectronics manufacturing plasma processes. Going beyond plasma processes for fabrication of electronic devices, PPD sensors could be used for monitoring of atoms, molecules, ions, radicals, clusters, and particles in a variety of other settings, including outer space. Because of their high sensitivity, such sensors could also prove useful for detecting traces of illegal drugs and explosives.

Bolshakov, Alexander↗
DOE OSTI2020

SympNets: Intrinsic structure-preserving symplectic networks for identifying Hamiltonian systems

Here, we propose new symplectic networks (SympNets) for identifying Hamiltonian systems from data based on a composition of linear, activation and gradient modules. In particular, we define two classes of SympNets: the LA-SympNets composed of linear and activation modules, and the G-SympNets composed of gradient modules. Correspondingly, we prove two new universal approximation theorems that demonstrate that SympNets can approximate arbitrary symplectic maps based on appropriate activation functions. We then perform several experiments including the pendulum, double pendulum and three-body problems to investigate the expressivity and the generalization ability of SympNets. The simulation results show that even very small size SympNets can generalize well, and are able to handle both separable and non-separable Hamiltonian systems with data points resulting from short or long time steps. In all the test cases, SympNets outperform the baseline models, and are much faster in training and prediction. We also develop an extended version of SympNets to learn the dynamics from irregularly sampled data. This extended version of SympNets can be thought of as a universal model representing the solution to an arbitrary Hamiltonian system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Imaging two-dimensional generalized Wigner crystals

The Wigner crystal has fascinated condensed matter physicists for nearly 90 years. Signatures of two-dimensional (2D) Wigner crystals were first observed in 2D electron gases under high magnetic field, and recently reported in transition metal dichalcogenide moiré superlattices. Direct observation of the 2D Wigner crystal lattice in real space, however, has remained an outstanding challenge. Conventional scanning tunnelling microscopy (STM) has sufficient spatial resolution but induces perturbations that can potentially alter this fragile state. Here we demonstrate real-space imaging of 2D Wigner crystals in WSe 2 /WS 2 moiré heterostructures using a specially designed non-invasive STM spectroscopy technique. This employs a graphene sensing layer held close to the WSe 2 /WS 2 moiré superlattice. Local STM tunnel current into the graphene layer is modulated by the underlying Wigner crystal electron lattice in the WSe 2 /WS 2 heterostructure. Different Wigner crystal lattice configurations at fractional electron fillings of n = 1/3, 1/2 and 2/3, where n is the electron number per site, are directly visualized. The n = 1/3 and n = 2/3 Wigner crystals exhibit triangular and honeycomb lattices, respectively, to minimize nearest-neighbour occupations. The n = 1/2 state spontaneously breaks the original C3 symmetry and forms a stripe phase. Here our study lays a solid foundation for understanding Wigner crystal states in WSe 2 /WS 2 moiré heterostructures and provides an approach that is generally applicable for imaging novel correlated electron lattices in other systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Comparison of PID Shunting in Polycrystalline and Single-Crystal Silicon Modules via Multi-Scale, Multi-Technique Characterization

We used the methods we reported last year to investigate potential-induced degradation (PID). We have now applied these methods to single-crystalline silicon modules that have degraded during field deployment, as well as in minimodules stressed in the laboratory. We will compare these results to the polycrystalline results presented last year. Small cores have been removed from the modules and subjected to analysis. We use a combination of photoluminescence and dark lock-in thermography imaging, laser marking, electron-beam induced current measurements, and subsequent focused ion-beam marking to allow analysis of individual defects via time-of-flight secondary-ion mass spectrometry (TOF-SIMS) to investigate the root-cause mechanism for PID shunting. We see a direct correlation between recombination active shunts and sodium content. The sodium content in shunted areas peaks at the SiN/Si interface and is consistently observed at a concentration of 0.1%-1% in shunted areas. TOF-SIMS data taken on degraded and non-degraded single-crystalline sample areas show a similar trend as in the polycrystalline samples: more sodium is seen in the degraded areas.

14 SOLAR ENERGY↗
DOE OSTI2024

Exploring magnetic anisotropy and robustness of the J eff = 1/2 state under substantial orthorhombic distortion in Sr 2 IrO 4 thin films

Here, we present a comprehensive study revealing the intricate interplay of the magnetic anisotropy and orthorhombic distortion in thin films of Sr 2 IrO 4 through a Ca 3 Ru 2 O 7 substrate. By inducing a pronounced orthorhombic distortion along the direction of oxygen octahedral edges, we effectively modulated the uniaxial magnetic anisotropy in the system. Remarkably divergent responses along the easy and hard magnetic axes were unveiled through x-ray magnetic circular dichroism (XMCD) measurements under magnetic fields. Specifically, the spin flop transition observed when the magnetic field aligns with the hard axis allows us to estimate the magnetic anisotropy energy, which is around 14.2 µeV, close to that estimated from the single magnon peak measured via Raman spectroscopy. The observed anisotropy energy remains notably lower than the linear estimates derived from the strain-anisotropy energy relationship outlined in H.-H. Kim et al., Nat. Commun. 13, 6674 (2022). This underscores the enduring preservation of the isotropic character of the J eff = 1/2 states. This is also supported by the negligible XMCD intensity ratio at the L 2 edge compared to that of the L 3 edge. Furthermore, the branching ratio determined from x-ray absorption spectroscopy shows that the expectation value of the spin-orbit coupling is similar to that of bulk Sr 2 IrO 4 single crystals. Our findings indicate that even under a substantial anisotropic biaxial distortion, Sr 2 IrO 4 remains remarkably proximate to the J eff = 1/2 state. This study not only provides valuable information in understanding the interplay between magnetic anisotropy and strain but also the robustness of the J eff = 1/2 state under octahedral distortion within materials exhibiting emergent quantum phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Deep level transient spectroscopy investigation of ultra-wide bandgap ($\bar201$) and ($001$) β -Ga 2 O 3

Here, this work reports on a comprehensive examination of the electrical and thermal properties of vertical Schottky diodes fabricated on ($\bar201$) and ($001$)-oriented samples of β-Ga 2 O 3 . The temperature-dependent current–voltage (I–V) and capacitance–voltage (C–V) data were gathered and analyzed down to 60 K. Deep level transient spectroscopy (DLTS) was used to study bulk and interface defects in the two materials from approx. 325 K down to 60 K. In the bulk ($\bar201$) material, an electron trap was observed at E C -0.46 eV, with a capture cross section of 1.6 x 10 -14 cm 2 and a lambda-corrected maximum trap density of 9.08 x 10 15 cm -3 . These results and others indicate that the electron trap is a strong candidate for the well-known E1 defect in β-Ga 2 O 3 based on recent investigations. Additionally, in the ($\bar201$) material, the smooth modulation typical of interface states is evident at temperatures below 275 K. The ($001$) samples manifested what is likely the E2* electron trap at E C -0.68 eV, with a capture cross section of 1.64 x 10 -15 cm 2 and a lambda-corrected maximum trap density of 8.85 x 10 15 cm -3 . The presence of the E2* defect, in particular, is a contrast to the findings of recent DLTS investigations on β-Ga 2 O 3 , which report that E2* emerged only after low-energy proton irradiation. These results help to further map out the defect signatures found in β-Ga 2 O 3 materials, which are of vital importance in the design and fabrication of future β-Ga 2 O 3 devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗