Energy Window Research Articles

Numerical simulation and method study of X-ray litho-density logging

To effectively replace the isotope radiation source in litho-density logging, this study presents a method for measuring the formation density and photoelectric absorption index (Pe) using a switchable X-ray tube. First, the gamma-ray litho-density logging (GLD) method for measuring formation density and Pe using chemical sources is introduced. Then, a benchmark verification based on the X-ray litho-density logging tool prototype and data published by Simon (In: Paper presented at the SPWLA 59th annual logging symposium, London, UK, 2018) was carried out using Monte Carlo numerical simulations. Second, the impacts of the photoelectric effect and detector statistical error on the GLD method were analyzed. Finally, based on a theoretical analysis, the formation density and Pe measurement algorithm (double energy window (DEW) method) was improved, which was found to be suitable for X-ray litho-density logging. Moreover, the results obtained using this algorithm were compared with those obtained using the GLD method. The results indicate that owing to the impact of photoelectric effect and detector statistical error on the density energy window, the accuracy of formation density and Pe measurement using the GLD method is relatively low, with the uncertainty in formation density and Pe measurement reaching 2.620 ± 0.047 g/cm3 and 4.090 ± 0.580 b/e, respectively. In comparison, the DEW method can improve the accuracy of density and Pe measurement to 0.006 g/cm3 and 0.065 b/e, respectively, as the photoelectric effect in the density window is corrected using the counts in the lithology window of the energy spectrum. This study aims to provide a new theoretical foundation for processing X-ray litho-density logs in the future.

New measurements of cross sections and S-factors for $$d(p,\gamma )^{3}\text{He}$$ reaction at BBN energies

This communication is a summary of our measurements of cross sections and astrophysical S-factors for radiative proton capture on deuteron. The measurements are a part of a new program to study light-ion induced nuclear capture and inelastic scattering reactions relevant to nucleosynthesis and astrophysics. We are primarily interested in the capture reactions relevant to primordial or Big Bang Nucleosynthesis (BBN). Section 1 provides a brief and general overview of nuclear astrophysics and the primary experimental challenges in the measurements of cross sections and S-factors for reactions relevant to nuclear astrophysics. The next section discusses the significance of the $$d(p,\gamma )^{3}\text{He}$$ reaction in context of BBN and the need for generating a more precise data in the relevant energy window. The subsequent section is devoted to the experiment and results of measurements of cross sections and astrophysical S-factors for the $$d(p,\gamma )^{3}\text{He}$$ reaction at three new BBN energies. One salient features of the measurements is the use of large volume LaBr $$_{3}$$ :Ce scintillation detector for measurement of the capture $$\gamma $$ -rays. To the best of our knowledge, capture $$\gamma $$ -rays for this reaction had so far been measured with NaI(Tl) or HPGe detectors only. The detection efficiency of the detector has been measured experimentally for different monochromatic $$\gamma $$ -ray energies. In addition, realistic GEANT4 Monte Carlo simulations have been carried out to generate the response of the detector for $$\gamma $$ -ray energies of interest. The measured cross section and astrophysical S(E)-factor for the three incident proton energies are found to be in agreement with the overall trend of the global data set for the BBN region, reported in the literature. The measured S-factors are also found to be in agreement with recent microscopic calculations of Marcucci et al. (2016).

Modulating tunneling width and energy window for high-on-current two-dimensional tunnel field-effect transistors

As a strong candidate for future electronics, tunnel field-effect transistors (TFETs) have attracted great attention recently due to their steep subthreshold swing and low power consumption. However, the low on-state current has been regarded as the major challenge toward high-performance (HP) applications. Herein, we propose a device architecture strategy to modulate the tunneling probability and achieve high on-state current taking boron phosphide (BP) 5-nm-gate TFETs as a case. By introducing different architectures and performing abundant simulation, a comprehensive study is performed to explore the intrinsic association between architecture and tunneling probability of 5 nm BP TFET. Particularly, derived from the effective modulation of tunneling width and energy window, 5 nm BP TFET with the spacer and pocket structures displays a large on-state current of 1506 μA/μm. Also, 5 nm BP TFET demonstrates the expected figures of merits for digital electronics and circuits compliant with the International Technology Roadmap for Semiconductors requirements for HP applications. Our findings will promote the development of 2D materials and device architectures for HP TFETs.

Design and performance of SIAT aPET: a uniform high-resolution small animal PET scanner using dual-ended readout detectors

In this work, a small animal PET scanner named SIAT aPET was developed using dual-ended readout depth encoding detectors to simultaneously achieve high spatial resolution and high sensitivity. The scanner consists of four detector rings with 12 detector modules per ring; the ring diameter is 111 mm and the axial field of view (FOV) is 105.6 mm. The images are reconstructed using an ordered subset expectation maximization (OSEM) algorithm. The spatial resolution of the scanner was measured by using a 22Na point source at the center axial FOV with different radial offsets. The sensitivity of the scanner was measured at center axis of the scanner with different axial positions. The count rate performance of the system was evaluated by scanning mouse-sized and rat-sized phantoms. An ultra-micro hot-rods phantom and two mice injected with 18F-NaF and 18F-FDG were scanned on the scanner. An average depth of interaction (DOI) resolution of 1.96 mm, energy resolution of 19.1% and timing resolution of 1.20 ns were obtained for the detector. Average spatial resolutions of 0.82 mm and 1.16 mm were obtained up to a distance of 30 mm radially from the center of the FOV when reconstructing a point source in 1% and 10% warm backgrounds, respectively, using OSEM reconstruction with 16 subsets and 10 iterations. Sensitivities of 16.0% and 11.9% were achieved at center of the scanner for energy windows of 250–750 keV and 350–750 keV respectively. Peak noise equivalent count rates (NECRs) of 324 kcps and 144 kcps were obtained at an activity of 26.4 MBq for the mouse-sized and rat-sized phantoms. Rods of 1.0 mm diameter can be visually resolved from the image of the ultra-micro hot-rods phantom. The capability of the scanner was demonstrated by high quality in-vivo mouse images.

A dissymmetric [Gd2] coordination molecular dimer hosting six addressable spin qubits

Artificial magnetic molecules can host several spin qubits, which could then implement small-scale algorithms. In order to become of practical use, such molecular spin processors need to increase the available computational space and warrant universal operations. Here, we design, synthesize and fully characterize dissymetric molecular dimers hosting either one or two Gadolinium(III) ions. The strong sensitivity of Gadolinium magnetic anisotropy to its local coordination gives rise to different zero-field splittings at each metal site. As a result, the [LaGd] and [GdLu] complexes provide realizations of distinct spin qudits with eight unequally spaced levels. In the [Gd2] dimer, these properties are combined with a Gd-Gd magnetic interaction, sufficiently strong to lift all level degeneracies, yet sufficiently weak to keep all levels within an experimentally accessible energy window. The spin Hamiltonian of this dimer allows a complete set of operations to act as a 64-dimensional all-electron spin qudit, or, equivalently, as six addressable qubits. Electron paramagnetic resonance experiments show that resonant transitions between different spin states can be coherently controlled, with coherence times TM of the order of 1 µs limited by hyperfine interactions. Coordination complexes with embedded quantum functionalities are promising building blocks for quantum computation and simulation hybrid platforms.

Engineering silicon-carbide quantum dots for third generation photovoltaic cells.

Interested in the recent development of the building up of photovoltaic devices using graphene-like quantum dots as a novel electron acceptor; we study in this work the optoelectronic properties of edge-functionalized SiC quantum dots using the first principles density functional. For an accurate quantitative estimation of key parameters, a many-body perturbation theory within GW approximation is also performmed. We examine the ability to tailor the electronic gap and optical absorption of the new class of QDs through hydroxylation and carboxylation of seam atoms, in order to improve their photovoltaic efficiency. The HOMO-LUMO energy gap was significantly altered in terms of the type, the concentration and the position of functional groups. The spatial charge separation and charge transfer characterizing our systems seem very prominent to use as dye-sensitized solar cells. Furthermore, the optical band gap of all our compounds is in the NIR-visible energy window, and exhibits a magnitude smaller than that calculated in the pristine case, which enhances the photovoltaic efficiency. Likewise, absorption curves, exciton binding energy and singlet-triplet energy splitting have been broadly modified by functionalization confirming the great luminescent yield of SiCQDs. Depending on the size, SiC quantum dots absorb light from the visible to the near-infrared region of the solar spectrum, making them suitable for third generation solar cells.

Performance assessment of the ALBIRA II pre-clinical SPECT S102 system for 99mTc imaging.

The performance characteristics of the SPECT sub-system S102 of the ALBIRA II PET/SPECT/CT are analyzed for the 80mm field of view (FOV) to evaluate the potential in-vivo imaging in rats, based on measurements of the system response for the commonly used Technetium-99m (99mTc) in small animal imaging. The ALBIRA II tri-modal µPET/SPECT/CT pre-clinical system (Bruker BioSpin, Ettlingen, Germany) was used. The SPECT modality is made up of two opposite gamma cameras (Version S102) with Sodium doped Cesium Iodide (CsI(Na)) single continuous crystal detectors coupled to position-sensitive photomultipliers (PSPMTs). Imaging was performed with the NEMA NU-4 image quality phantom (Data Spectrum Corporation, Durham, USA). Measurements were performed with a starting activity concentration of 4.76MBq/mL 99mTc. An energy window of 20% at 140keV was selected in this study. The system offers a 20mm, 40mm, 60mm and an 80mm field of view (FOV) and in this study the 80mm FOV was used for all the acquisitions. The data were reconstructed with an ordered subset expectation maximization (OSEM) algorithm. Sensitivity, spatial resolution, count rate linearity, convergence of the algorithm and the recovery coefficients (RC) were analyzed. All analyses were performed with PMOD and MATLAB software. The sensitivities measured at the center of the 80mm FOV with the point source were 23.1 ± 0.3 cps/MBq (single pinhole SPH) and 105.6 ± 5.5 cps/MBq (multi pinhole MPH). The values for the axial, tangential and radial full width at half maximum (FWHM) were 2.51, 2.54, and 2.55mm with SPH and 2.35, 2.44 and 2.32mm with MPH, respectively. The corresponding RC values for the 5mm, 4mm, 3mm and 2mm rods were 0.60 ± 0.28, 0.61 ± 0.24, 0.29 ± 0.11 and 0.20 ± 0.06 with SPH and 0.56 ± 0.20, 0.50 ± 0.18, 0.38 ± 0.09 and 0.23 ± 0.06 with MPH. To obtain quantitative imaging data, the image reconstructions should be performed with 12 iterations. The ALBIRA II preclinical SPECT sub-system S102 has a favorable sensitivity and spatial resolution for the 80mm FOV setting for both the SPH and MPH configurations and is a valuable tool for small animal imaging.

Evaluation of a Hamamatsu TOF-PET Detector Module With 3.2-mm Pitch LFS Scintillators and a 256-Channel SiPM Array

Using time-of-flight (TOF) information in image reconstruction improves image signal-to-noise ratio and quantitative accuracy in positron emission tomography (PET). A new TOF-PET detector module with a 3.2-mm pitch lutetium fine silicate (LFS) scintillator array one-to-one coupled to a 16×16 (256-ch) silicon photomultiplier (SiPM) array was made commercially available (C13500 series, Hamamatsu Photonics K. K.). In this study, as a candidate detector module for the next-generation brain-dedicated PET, we changed the scintillator length of 20 to 10 mm according to our helmet-type PET geometry and investigated the basic performance of the PET detector module, including its energy resolution, sensitivity, coincidence response function (CRF), and coincidence timing resolution (CTR). All performance values were compared with those of the 4.2-mm pitch 144-ch detector module which was selected for our current helmet-type PET prototype. The energy resolution was 12% at 511 keV. The sensitivity was about 10% lower compared with those of the 4.2-mm pitch module. The average full width at half maximum (FWHM) of the CRFs was 1.9 mm. The CTRs had values of 235-241 ps with various energy windows after applying timing calibration. The CTR was not significantly changed (<; 10 ps) at the single count rate of 412 kcps or lower.

Structural, electronic, and excitonic properties of few-layer SeS2 and TeS2

High-efficiency optoelectronic devices require materials with suitable band gap, excellent carrier mobility, strong light-matter interaction, and high thermal- and photostability. Herein, we report two layered materials of group VI, namely, $\mathrm{Se}{\mathrm{S}}_{2}$ and $\mathrm{Te}{\mathrm{S}}_{2}$, which meet all those desired criteria. Both materials are stable with 1T-$\mathrm{Mo}{\mathrm{S}}_{2}$-like structure, and exhibit in-direct gap semiconducting feature and possess extraordinary electronic transport properties with isotropic carrier mobilities outperforming their $\mathrm{Mo}{\mathrm{S}}_{2}$ analog. Using the $GW$ approach for determining the quasiparticle electronic structure and Bethe-Salpeter equation accounting for the many-body excitonic effects, the optical properties of both materials have been identified. We find that exciton effects are significant in both materials that is characterized by the large binding energy of 0.66 and 0.84 eV for monolayer $\mathrm{Se}{\mathrm{S}}_{2}$ and $\mathrm{Te}{\mathrm{S}}_{2}$, respectively. The absorption edges lie in the optimal energy window of $1.0\text{--}1.5\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, which enables strong photoabsorption covering the whole visible-light region. Finally and importantly, we demonstrate that the in-direct nature of those materials can be violated by capping them with 2H-$\mathrm{Mo}{\mathrm{S}}_{2}$ to form a van der Waals heterostructure, while keeping the gap in the energy favorable region. Those physical and optical characteristics make few-layer $\mathrm{Se}{\mathrm{S}}_{2}$ and $\mathrm{Te}{\mathrm{S}}_{2}$ highly appealing for room-temperature light-emitting devices and, particularly, solar harvesting devices.

Short-periodic-orbit method for excited chaotic eigenfunctions.

An alternative method for the calculation of excited chaotic eigenfunctions in arbitrary energy windows is presented. We demonstrate the feasibility of using wave functions localized on unstable periodic orbits as efficient basis sets for this task in classically chaotic systems. The number of required localized wave functions is only of the order of the ratio t_{H}/t_{E}, with t_{H} the Heisenberg time and t_{E} the Ehrenfest time. As an illustration, we present convincing results for a coupled two-dimensional quartic oscillator with chaotic dynamics.

Collimator and Energy Window Evaluation in Ga-67 Imaging by Monte Carlo Simulation

Objectives:Gallium-67 (Ga-67) imaging is affected by collimator penetration and scatter components owing to the high-energy (HE) gamma-ray emissions. The characterization of penetration and scatter distribution is essential for the optimization of low-energy high-resolution (LEHR), medium energy (ME), and HE collimators and for the development of an effective correction technique. We compared the image quality that can be achieved by 3 collimators for different energy windows using the SIMIND Monte Carlo code.Methods:Simulation experiments were conducted for LEHR, ME, and HE collimators for Ga-67 point source placed at 12-cm distance from the detector surface using the Monte Carlo SIMIND simulation code. Their spectra point spread functions as well as the original, penetration, scattering, and X-rays curves were drawn and analyzed. The parameters full-width at half maximum and full-width at tenth maximum were also investigated.Results:The original, penetration, and scatter curves within 10% for LEHR were 34.46%, 33.52%, 17.29%, and 14.72%, respectively. Similarly, the original, penetration, scatter, and X-rays within 10% for ME and HE were 83.06%, 10.25%, 6.69%, and 0% and 81.44%, 11.51%, 7.05%, and 0%, respectively. The trade-off between spatial resolution and sensitivity was achieved by using the ME collimator at 185 photopeak of Ga-67.Conclusion:The Monte Carlo simulation outcomes can be applied for optimal collimator designing and for the development of new correction method in Ga-67 imaging.

On the Spectral Peak Energy of Swift Gamma-Ray Bursts

Abstract Owing to the narrow energy band of the Swift Burst Alert Telescope (BAT), several urgent issues remain unsolved. We systematically study the properties of a refined sample of 283 Swift/BAT gamma-ray bursts (GRBs) with well-measured spectral peak energy (E p) at a high confidence level greater than 3σ. We find that the duration (T 90) distribution of Swift bursts still exhibits an evident bimodality with a more reliable boundary of T 90 ≃ 1.06 s instead of 2 s as found for previously contaminated samples, including bursts without well-peaked spectra, which is very close to the ∼1.27 and ∼0.8 s values suggested in the literature for the Fermi/Gamma-ray Burst Monitor and Swift/BAT catalogs, respectively. The Swift/BAT short and long bursts have comparable mean E p values of and keV, similar to what was found for both types of BATSE bursts, which indicates that the traditional short–hard/long–soft scheme may not be tenable for certain detector energy windows. We also statistically investigate the consistency of distinct methods for E p estimates and find that a Bayesian approach and BAND function (Band et al.) can always provide consistent evaluations. In contrast, the frequently used cutoff power-law model matches two other methods for lower E p and overestimates the E p by more than 70%, as E p &gt; 100 keV. Peak energies of X-ray flashes, X-ray-rich bursts, and classical GRBs could be an evolutionary consequence of moving from thermal-dominated to nonthermal-dominated radiation mechanisms. Finally, we find that the E p and the observed fluence (S γ ) in the observer frame are correlated as keV, which might be a useful indicator of GRB peak energies.

Collimator and energy window optimization for YTTRIUM-90 bremsstrahlung SPECT imaging

The optimal collimator and energy window for Yttrium-90 bremsstrahlung SPECT imaging was investigated in the study. Yttrium-90 images were acquired with a dual-head gamma camera, equipped with parallel hole collimators and 90Y vial for different energy windows ranging from 56 to 232 keV. Image quality parameters (sensitivity, %FOV, and S/B) were examined for the energy window and collimator combinations. It is concluded that the optimal SPECT imaging was achieved using FBP Method with a HEGP collimator and the energy window of 90–110 keV.

Quantitative Monte Carlo-based brain dopamine transporter SPECT imaging.

Brain dopamine transporter imaging with I-123-labeled radioligands is technically demanding due to the small size of the imaging target relative to the spatial resolution of most SPECT systems. In addition, I-123 has high-energy peaks which can penetrate or scatter in the collimator and be detected in the imaging energy window. The aim of this study was to implement Monte Carlo (MC)-based full collimator-detector response (CDR) compensation algorithm for I-123 into a third-party commercial SPECT reconstruction software package and to evaluate its effect on the quantitative accuracy of dopaminergic-image analysis compared to a method where only the geometric component of the CDR is compensated. In this work, we utilized a full Monte Carlo collimator-detector model and incorporated it into an iterative SPECT reconstruction algorithm. The full Monte Carlo model reconstruction was compared to standard reconstruction using an anthropomorphic striatal phantom filled with different I-123 striatal/cortex uptake ratios and with clinical I-123 Ioflupane DaTScan studies. Reconstruction with the full model yielded higher (13-25%) striatal uptake ratios than the conventional reconstruction, but the uptake ratios were still much lower than the true ratios due to partial volume effect. Visually, images reconstructed with the full Monte Carlo model had better contrast and resolution than the conventional images, with both phantom and patient studies. Reconstruction with full Monte Carlo collimator-detector model yields higher quantitative accuracy than conventional reconstruction. Additional work to reduce the partial volume effect related errors would improve the accuracy further.

Suppressing Ambipolar Current in UTFET by Auxiliary Gate

In this paper, a new U-shaped channel tunneling-based field-effect transistor (UTFET) with auxiliary gate above drain is proposed. The ambipolar current in the proposed is investigated, in which simulation results show that ambipolar current takes place, due to drain-to-drain tunneling similar to gate-induced drain leakage in conventional MOSFETs. By drain depletion in auxiliary gate-based UTFET, electric field is reduced in ambipolar tunneling region, which causes tunneling barrier width to increase and the energy window of tunneling (ΔΦ) to decrease. As a result, two decades of reduction in the ambipolar current is achieved and ambipolar subthreshold swing (SSamb) is degraded by 24.8% in comparison with similar structure without auxiliary gate.

Lattice contrast in the core-loss EFTEM signal of graphene

The realization of chromatic aberration correction enables energy-filtered transmission electron microscopy (EFTEM) at atomic resolution even for large energy windows. Previous works have demonstrated lattice contrast from ionization-edge signals such as the L2,3 edges of silicon or titanium. However, the direct interpretation as chemical information was found to be hampered by contributions from elastic contrast with dynamic scattering, especially for thick samples. Here we demonstrate that even for thin samples with light atoms, the interpretation of the ionization-edge signal is complicated by inversions from bright-atom to dark-atom contrast. Our EFTEM experiments for graphene show lattice contrast in the carbon K-edge signal, and we find bright-atom and dark-atom contrast for different defoci.

Controlled giant magnetoresistance and spin–valley transport in an asymmetrical MoS2 tunnel junction

We study the effects of asymmetrical magnetization and an optoelectronic tunable band structure on the transmission of particles in a MoS2 tunnel junction. Based on the results, we propose a model for a multifunctional coupler as a single system incorporating giant magnetoresistance, a spin–valley filter, and a spin–valley valve. The device is made up of ferromagnetic/ferromagnetic/normal junctions, with an off-resonant light and an electric gate potential functioning as the spin–valley filter and spin–valley valve, respectively. Increasing the asymmetrical magnetization is found to substantially enhance the tunneling magnetoresistance (TMR) of the system, leading to giant TMR. The spin–valley filtering is based on the spin imbalance modulation that arises from asymmetrical magnetization and the valley degeneracy breaking of off-resonant light, and the spin–valley valve is produced by altering the effective density of states of spin/valley polarized bands via the gate potential that controls the flow of spin/valley polarized particles. By fixing the magnetization configurations, one specific spin–valley filter and spin–valley valve can be acquired by tuning an external parameter to the corresponding spin/valley polarized energy windows.

Evaluation of a Correction Method for 111In-Pentetreotide SPECT Imaging of Gastroenteropancreatic Neuroendocrine Tumors.

The number of patients with the extremely rare disease gastroenteropancreatic (GEP) neuroendocrine tumor (NET) has increased rapidly in recent years. 111In-pentetreotide SPECT in somatostatin receptor scintigraphy has been used for the assessment of GEP NET patients. To diagnose GEP NET, appropriate selection of image correction parameters is critical. Correction methods may improve the 111In-pentetreotide SPECT image quality, but there is currently no standard technique. The purpose of this study was to determine the optimal correction parameter settings for 111In-pentetreotide SPECT. Methods: A phantom study produced images with a tumor-to-background ratio of as high as 16:1. A triple energy window was used for scatter correction (SC), and attenuation correction (AC) was CT-based. Correlation analysis was performed in 4 groups: no correction (NC), SC, AC, and combined SC with AC (CC). The 111In-pentetreotide SPECT results for 20 randomly selected patients (13 men and 7 women; age range, 37-81 y) with confirmed GEP NET were analyzed using data collected 4 h after injection of 111 MBq of 111In-pentetreotide. Emission data were reconstructed using ordered-subset expectation maximization (OSEM) with different settings. Different combinations of the correction parameters were used to analyze the contrast-to-noise ratios (CNRs) obtained with the phantom. In the clinical study, 20 GEP NET patients were used to evaluate the GEP NET lesion CNR by 4 different image correction methods obtained from 111In-pentetreotide SPECT images: NC, SC, AC, and CC. NC was used as a reference method. Results: The phantom study revealed that the optimal energy window in the photopeak for somatostatin receptor scintigraphy was 171 keV ± 10% and 245 keV ± 7.5%, and the optimal OSEM reconstruction conditions were 8 subsets and 6 iterations. Among the OSEM collection conditions, CC produced a significantly higher CNR than NC or SC (P < 0.05). In the clinical study, CC was found to increase the CNR (P < 0.05). Conclusion: CC improves the correction in 111In-pentetreotide SPECT studies, compared with NC, providing better contrast and sharper outlines of lesions and organs.

Uncovering Non-Fermi-Liquid Behavior in Hund Metals: Conformal Field Theory Analysis of an SU(2)×SU(3) Spin-Orbital Kondo Model

Hund metals have attracted attention in recent years due to their unconventional superconductivity, which supposedly originates from non-Fermi-liquid (NFL) properties of the normal state. When studying Hund metals using dynamical mean-field theory, one arrives at a self-consistent "Hund impurity problem" involving a multiorbital quantum impurity with nonzero Hund coupling interacting with a metallic bath. If its spin and orbital degrees of freedom are screened at different energy scales, $T_\mathrm{sp} < T_\mathrm{orb}$, the intermediate energy window is governed by a novel NFL fixed point, whose nature had not yet been clarified. We resolve this problem by providing an analytical solution of a paradigmatic example of a Hund impurity problem, involving two spin and three orbital degrees of freedom. To this end, we combine a state-of-the-art implementation of the numerical renormalization group, capable of exploiting non-Abelian symmetries, with a generalization of Affleck and Ludwig's conformal field theory (CFT) approach for multichannel Kondo models. We characterize the NFL fixed point of Hund metals in detail for a Kondo model with an impurity forming an SU(2)$\times$SU(3) spin-orbital multiplet, tuned such that the NFL energy window is very wide. The impurity's spin and orbital susceptibilities then exhibit striking power-law behavior, which we explain using CFT arguments. We find excellent agreement between CFT predictions and numerical renormalization group results. Our main physical conclusion is that the regime of spin-orbital separation, where orbital degrees of freedom have been screened but spin degrees of freedom have not, features anomalously strong local spin fluctuations: the impurity susceptibility increases as $\chi_\mathrm{sp}^\mathrm{imp} \sim \omega^{-\gamma}$, with $\gamma > 1$.

Tuning the electronic and magnetic properties of pentagraphene through the C1 vacancy

Pentagraphene (PG), a two-dimensional allotrope of carbon with only five-membered rings, was recently predicted to exhibit a wide band gap, an unusual negative Poisson’s ratio, and robust dynamical and thermal stability. However, its potential properties arising from defect engineering of five-membered rings have not been explored yet. In this work, we explore the C1 vacancy in PG using first-principles density functional calculations. The formation energy of this vacancy is surprisingly within the formation energy window of monovacancy (MV) in graphene. This defect introduces eight midgap levels indicating the possibility of studying the charge states. The charged defect is amphoteric with deep donor and deep acceptor levels. Introducing the vacancy in the sheet renders it inherently ferromagnetic (FM) with a magnetic moment of 4 µB. Upon further investigating spin polarization in PG, three possible unique magnetic configurations are found to exist: FM, ferrimagnetic (FiM), and anti-ferromagnetic (AFM). The energy difference between the FM and the FiM (AFM) states is ∼−62.4 meV atom−1 (∼−81.9 meV atom−1). Despite FiM and AFM being lower in energy, interestingly, this intrinsic FM ordering of spins is preserved even when the defect concentration is increased. This observation would probably hint at the existence of a kinetic barrier between FM and AFM states which merits further investigations.