Effect of Metal d Band Position on Anion Redox in Alkali-Rich Sulfides
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25 ENERGY STORAGE↗
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Interstitial Nature of Mn 2+ Doping in 2D Perovskites
Halide perovskites doped with magnetic impurities (such as the transition metals Mn 2+ , Co 2+ , Ni 2+ ) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs 2 PbI 2 Cl 2 , we show that doping Mn 2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn 2+ does not replace the Pb 2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn 2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn 2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl – and two I – atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Toroidal modeling of runaway electron loss due to 3-D fields in DIII-D and COMPASS
The 3-D field induced relativistic runaway electron (RE) loss has been simulated for DIII-D, COMPASS and ITER plasmas, utilizing the MARS-F code incorporated with the recently developed and updated RE orbit module (REORBIT). Modeling shows effectively 100% loss of a post-disruption, high-current runaway beam in DIII-D, due to the 1 kG level of magnetic field perturbation produced by a fast growing n = 1 resistive kink instability. The RE loss is shown to be independent of the particle energy or the initial location of particles in the configuration space. Applied resonant magnetic perturbation (RMP) fields from in-vessel coils are not effective for RE beam mitigation in DIII-D, but do produce finite (>10%) RE loss in COMPASS, consistent with experimental observations in above two devices. The major reasons for this difference in RE control by RMP between these two devices are (i) the coil proximity to the RE beam and (ii) the effective coil current scaling versus the machine size and the toroidal magnetic field. About 10% RE loss fraction is also predicted for an ITER 15 MA scenario with pre-disruption plasma, highlighting the role of the plasma response. Up to 30% loss is computed, however, by artificially scaling the equilibrium pressure to zero. This is due to the more resistive plasma response and stronger resulting field line stochasticity. Distributions of the lost REs to the limiting surface show poloidally peaked profile near the high-field-side in both DIII-D and COMPASS, covering about 100o poloidal angle. Higher perturbation field level and/or higher particle energy also result in REs being lost to the low-field-side of the limiting surface of these two devices, increasing the effective wetted area. Finally, for the modeled ITER plasmas, the applied RMP field, with optimal poloidal spectrum that maximizes the edge localized mode control, leads to REs being lost to the lower divertor region of the limiting surface within a narrow poloidal band.
3-D field↗
Prototypes of Nonrelativistic Spin Splitting and Polarization in Symmetry Broken Antiferromagnets
Antiferromagnets that break both space-time reversal and translation-spin-rotation symmetries were recently predicted [L.-D. Yuan, Z. Wang, J.-W. Luo, E. I. Rashba, and A. Zunger, Phys. Rev. B 102, 014422 (2020)] to possess splitting between the otherwise spin-degenerate energy bands even without the relativistic spin-orbit coupling (SOC). Here, we point out that such nonrelativistic spin splitting (NRSS)—in particular, “spin splitting type 4” (SST-4) symmetry-broken antiferromagnets—can be divided into subgroups having distinct patterns of spin splitting and spin textures, depending on additional auxiliary symmetries of spin interconversion and polarity. These SST-4 subgroups include the 𝛼-type (no spin-interconverting symmetry) having spin splitting at the Brillouin zone center, as well as the 𝛽 subgroup in which a rotation symmetry is applied and determines the alternating spin texture and the 𝛾 subgroup having exclusively reflection spin-interconverting symmetry. Unlike ferrimagnets, the 𝛼-type compounds are shown to have tiny net magnetization at finite temperature and thus avoid the adverse effect of the stray field. The 𝛼 and 𝛽 subgroups can be either polar or nonpolar, whereas the 𝛾 subgroup is polar only, providing a basis for possible switching by external fields. The combination of NRSS-enabling and auxiliary symmetries is used here as a filter for identifying previously synthesized compounds as specific prototypes. Their characteristic splitting and spin polarization are calculated by density functional theory to the benefit of potential future experimental testing. Interesting results are as follows: (i) SOC-independent NRSS can exceed the magnitude of the SOC-induced Rashba and Dresselhaus spin splitting in semiconductors. (ii) Examples of predicted 𝛼-type insulating compounds include BiCrO 3 (nonpolar) and Mn 2 ScSbO 6 (polar), the latter having spin splitting of 158 meV and 160 meV in the valence and conduction bands, respectively. (iii) The 𝛽-type (Cu 2 Y 2 O 5 and FeF 2 ) and 𝛾-type compounds (Mn 4 Nb 2 O 9 and FeScO 3 ) are distinguished both by their auxiliary symmetries and polarity. The spin textures of 𝛾-type compounds are mirror reflected with spin degeneracy of the wave vectors on that mirror. These observations will likely broaden the experimental playing field of NRSS physics significantly.
antiferromagnets↗
Electronic correlations in the semiconducting half-Heusler compound FeVSb
Electronic correlations are crucial to the low-energy physics of metallic systems with localized d and f states; however, their effect on band insulators and semiconductors is typically negligible. Here, we measure the electronic structure of the half-Heusler compound FeVSb, a band insulator with a filled shell configuration of 18 valence electrons per formula unit ( s 2 p 6 d 10 ). Additionally, angle-resolved photoemission spectroscopy reveals a mass renormalization of m * / m bare = 1.4 , where m * is the measured effective mass and m bare is the mass from density functional theory calculations with no added on-site Coulomb repulsion. Our measurements are in quantitative agreement with dynamical mean-field theory calculations, highlighting the many-body origin of the mass renormalization. This mass renormalization lies in dramatic contrast to other filled shell intermetallics, including the thermoelectric materials CoTiSb and NiTiSn, and has a similar origin to that in FeSi, where Hund's coupling induced fluctuations across the gap can explain a dynamical self-energy and correlations. Our work calls for a rethinking of the role of correlations and Hund's coupling in intermetallic band insulators.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Signatures of van Hove singularities in the anisotropic in-plane optical conductivity of the topological semimetal Nb 3 SiTe 6
In this work, we present a temperature-dependent infrared spectroscopy study on the layered topological semimetal Nb 3 SiTe 6 combined with density-functional theory calculations of the electronic band structure and optical conductivity. Our results reveal an anisotropic behavior of the in-plane (ac-plane) optical conductivity, with three pronounced excitations located at around 0.15, 0.28, and 0.41 eV for the polarization of the incident radiation along the c axis. These excitations are well reproduced in the theoretical spectra. Based on the ab initio results, the excitations around 0.15 and 0.28 eV are interpreted as fingerprints of van Hove singularities in the electronic band structure and compared to the findings for other topological semimetals.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Level scheme study of 92 Mo: Searching for evidence of core excitation
Excited states in 92 Mo are populated via the 89 Y( 6 Li, 3$\textit{n}$) 92 Mo reaction at the tandem of XTU, INFN-LNL. The level scheme of 92 Mo is revised and expanded considerably by the γ-γ coincidence measurement. The newly observed level structures are compared with different shell-model calculations performed in various model spaces. In this work, the results show that the several high-energy (≈2 MeV) transitions, observed for the first time in the current work, could be a presumable signature of $\textit{N}$ = 50 core-breaking effect. The measured strengths of $\textit{E}$1 transitions between the low-lying positive and negative bands indicate an important contribution from $\textit{Z}$ = 28 proton core-excitation
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
A Monolithic O-Band Coherent Optical Receiver for Energy-Efficient Links
Not Available
Movaghar, Ghazal↗
Pinning of energy transitions of defects, complexes, and surface states in AlGaN alloys
In this work, we determine the dependence of the defect transition energies, electronic bands, and surface charge neutrality levels in AlGaN. With Vacuum level as reference, we show that energy transitions of localized defects and the surface Fermi level are independent of the alloy composition as electronic bands diverge with the increase in the bandgap as a function of alloy composition. The invariance of localized states on the alloy composition creates a convenient internal reference energy with respect to which other energy states may be measured. We demonstrate a higher generality to the universality rule with the independence of deep transition states of otherwise shallow donor type defects [(+1/+3) transition for VN] and defect complexes (C N +Si III ) in addition to the earlier predicted independent nature of mid-gap states when they are either the antibonding state between cationic impurities and host anion or acceptors at anion sites.
36 MATERIALS SCIENCE↗
Atomistic determination of Peierls barriers of dislocation glide in nickel
The Peierls barrier measures the lattice resistance to dislocation glide in crystalline solids. We use the nudged elastic band (NEB) method to calculate the Peierls barriers for screw and edge dislocation glide in a face-centered cubic (FCC) metal of Ni. The minimum energy paths (MEPs) across single or sequential Peierls barriers are determined under shear loading. The NEB results show the decreasing Peierls barrier with increasing shear stress, giving the Peierls stress at which the Peierls barrier vanishes. The effects of boundary condition and system size on Peierls barriers are studied by comparing strain- and stress-controlled NEB results. Furthermore, the free-end NEB methods are applied to determine MEPs with improved computational efficiency. The NEB results are also used to evaluate the energetic driving force of dislocation glide, which is consistent with that determined from the Peach-Koehler force. The accuracy of the present NEB results based on an empirical interatomic potential is assessed by comparison with a machine-learning potential. This work demonstrates the robust and efficient quantification of Peierls barriers to dislocation glide in an FCC metal, and it lays a solid foundation for the atomistic determination of Peierls barriers in compositionally complex alloys with the FCC structure in future studies.
42 ENGINEERING↗
Charge Carrier Lifetime Determination in Graded Absorber Solar Cells Using Time‐Resolved Photoluminescence Simulations and Measurements
Thin‐film photovoltaic device efficiencies are limited by carrier recombination, thus understanding recombination mechanisms is critical for performance improvements. Bulk minority carrier lifetime ( τ bulk ) is a critical parameter for solar cells but is difficult to determine in P–N junction devices, especially for high doping. As doping ≥10 16 cm −3 is required for efficient drift‐charge‐carrier‐collection devices, a method for τ bulk determination in doped P–N junction devices is necessary. This work utilizes time‐resolved photoluminescence (TRPL) simulations to quantify bulk and interface recombination properties in highly doped, graded absorber CdSeTe structures. The two methods developed here for τ bulk determination include utilization of an instantaneous lifetime representation to guide TRPL fitting and direct comparison between measured and simulated decays. Simulations verified that both methods are valid for state‐of‐the‐art device architectures which include graded bandgap absorbers, graded doping, and graded lifetimes. Shifts in the dominant recombination mechanism are identified for sufficiently long τ bulk , where front and back interface quality plays a more prominent role. Evaluation of surface recombination velocities and conduction band offset illustrate electro‐optical advantages of a positive conduction band offset and highlight the necessity of improved interfaces as bulk quality in photovoltaic devices improves.
14 SOLAR ENERGY↗
Exotic edge states of C 3 high-fold fermions in honeycomb lattices
A generalization of the graphene honeycomb model to the case where each site in the honeycomb lattice contains a n -fold degenerate set of eigenstates of the C 3 symmetry has been recently proposed to describe several systems, including triangulene crystals and photonic lattices. These generalized honeycomb models are defined by ( n a , n b ) , the number of C 3 eigenstates in the a and b sites of the unit cell, resulting in n a + n b bands. Thus, the (1,1) case gives the coventional honeycomb model that describes the two low-energy bands in graphene. Generalizations, such as (2,1), (2,2), and (3,3) display several nontrivial features, such as coexisting graphenelike Dirac cones with flat bands, both at zero and finite energy, as well as robust degeneracy points where a flat band and a parabolic band meet at the Γ point. Here we explore the edge states of this class of crystals, using as reference triangulene crystals, and we find several types of edge states absent in the conventional (1,1) honeycomb case, associated to the nontrivial features of the two-dimensional bands of the high-fold case. First, we find dispersive edge states associated to the finite-energy flat bands, that occur both at the armchair and zigzag termination. Second, in the case of noncentrosymmetric triangulene crystals that lead to a S = 1 Dirac band, we have a bonding-antibonding pair of dispersive edge states, localized in the same edge so that their energy splitting is reduced as their localization increases, opposite to the conventional behavior of pairs of states localized in opposite edges. Third, for the (3,3) case, that hosts a gap separating a pair of flat conduction and valence bands, we find nondispersive edge states with E = 0 in all edge terminations. Published by the American Physical Society 2024
Madail, L. (ORCID:0000000208457748)↗
Structural Stability of Tin-Lead Halide Perovskite Solar Cells
One of the key features that makes halide perovskite solar cells such an attractive and intensely researched photovoltaic (PV) technology, is the tunability of the bandgap of these halide perovskite materials [1], [2]. Shortly after it was established that the bandgap could be increased to 1.7-1.8 eV, investigations into the application for silicon based tandem solar cells launched. Within a few years, conversion efficiencies of up to 28 % have been reported [3]. Concurrently, the interest in commercial application of this technology emerged and have rapidly increased. Whereas there are advantages to piggy backing on an established PV technology such as silicon, efforts to develop all-perovskite tandem solar cells are of considerable interest. Partly substituting the metal cation in the ABX3 perovskite enables the low bandgap absorbers required for an all-perovskite tandem solar cell. One common approach is to partially substitute the lead with tin, however these materials often suffered from poor stability. Therefore the development of an efficient, stable mixed tin-lead perovskite is key to enabling all-perovskite tandem solar cells.
degradation↗
Exploration of signal processing methods for superconducting magnet and quench data
Quenching is the phenomenon of a superconducting magnetic material carrying current transitioning into a regular conducting material. This may cause severe and irreparable damage to the superconductor due to Joule heating. The Magnet Department at Fermi National Accelerator Laboratory (FNAL) has acquired experimental data through quench antenna arrays that are recorded when the quench is detected. These data are in terms of voltage signals that are sampled at 100kHz for several minutes. There are multiple channels and each channel provides a data set of more than 20 million observations, while there is one channel, called the trigger channel which shows the time when quench is detected. Despite some advancements that were made including machine learning, data complexity still shadows the progress. In this work, we studied a multi-resolution analysis of the quench antenna data through the Haar wavelet transform. In particular, we applied the maximally overlapped discrete w avelet transform (MODWT) of a suitable level L to the given data and then projected it onto the wavelet basis. This decomposes a given signal (Original data) $x ϵ \mathbb{R}^N$ into $L + 1$ subspaces of $\mathbb{R}^N$. One of the subspaces called the approximation, captures the trend of the signal, and the others, called the details, capture the fluctuations at different frequency bands. This decomposition provides a clear trend of the data at a suitable level and also various activities (spikes) are seen in the details of the decomposition at every level. These spikes might reveal some information about the quench under investigation but in any case, give information about magnet behavior. Also, this decomposition is seen to be very useful in removing noise present in the data due to the source or mechanism of the experiment.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing Intra-Halo Light with Galaxy Stacking in CIBER Images
We study the stellar halos of 0.2 ≲ $z$ ≲ 0.5 galaxies with stellar masses spanning $M$* ~ 10 10.5 to 10 12 $M$ ⊙ (approximately $L$* galaxies at this redshift) using imaging data from the Cosmic Infrared Background Experiment (CIBER). A previous CIBER fluctuation analysis suggested that intra-halo light (IHL) contributes a significant portion of the near-infrared extragalactic background light (EBL), the integrated emission from all sources throughout cosmic history. In this work, we carry out a stacking analysis with a sample of ~30,000 Sloan Digital Sky Survey (SDSS) photometric galaxies from CIBER images in two near-infrared bands (1.1 and 1.8 $μ$m) to directly probe the IHL associated with these galaxies. We stack galaxies in five sub-samples split by brightness and detect an extended galaxy profile beyond the instrument point-spread function (PSF) derived by stacking stars. We jointly fit a model for the inherent galaxy light profile plus large-scale one- and two-halo clustering to measure the extended galaxy IHL. We detect nonlinear one-halo clustering in the 1.8 $μ$m band at a level consistent with numerical simulations. Furthermore, by extrapolating the fraction of extended galaxy light, we measure to all galaxy mass scales, we find ~30%/15% of the total galaxy light budget from galaxies is at radius $r$ > 10/20 kpc, respectively. These results are new at near-infrared wavelengths at the $L$* mass scale and suggest that the IHL emission and one-halo clustering could have appreciable contributions to the amplitude of large-scale EBL background fluctuations.
79 ASTRONOMY AND ASTROPHYSICS↗
High Gradient Conditioning and Performance of C-Band β=0.5 Proton Normal- Conducting Copper and Copper-Silver Radio-Frequency Accelerating Cavities
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Zuboraj, M. R.A.↗