High-energy Band Research Articles

A Global Solution to a Slim Accretion Disk with Radiation-driven Outflows

Abstract The thickness of a slim disk is determined by the balance between the radiation force and the vertical component of the gravity of the black hole (BH). Vertical gravity is found to increase with the disk height, and it will decrease with the disk height if the disk thickness is above a critical value, which implies that gas at the disk surface may be driven into outflows by radiation force when the disk thickness surpasses the critical value. In this work, we derive a global solution to a slim disk with radiation-driven outflows. We find that the outflows are driven from the disk surface if the mass accretion rate is m ˙ ≳ 1.78 − 1.91 ( m ˙ = M ˙ / M ˙ Edd and M ˙ Edd = L Edd / 0.1 c 2 ) depending on the BH mass, while the outflows are suppressed when the mass accretion rate is lower than this critical value. The mass accretion rate decreases with the decreasing radius in the disk with outflows, and the rate of the gas swallowed by the BH is always limited to m ˙ in ∼ 1.78 − 1.91 even if the mass accretion rate at the outer edge of the disk is very high. This may set constraints on the massive BH growth through accretion in the early universe. Due to the presence of outflows, there is an upper limit on the radiation flux of the disk, which leads to saturation of the continuum spectra of the disk with outflows at the high-energy band. This may be tested by the observations of quasars or/and BH X-ray binaries.

Preparation and Photocatalytic Properties of CdS and ZnS Nanomaterials Derived from Metal Xanthate.

In this paper, we report a new, simple method for the synthesis of CdS and ZnS nanoparticles (NPs) prepared in a basic aqueous medium using metal xanthate as the sulfur source. The structure, morphology, size distribution, optical band gap, and photocatalytic properties of the newly obtained nanomaterials were investigated by UV-Vis spectroscopy, X-ray diffraction, and transmission electron microscopy. The results show that both CdS and ZnS crystallized in cubic phase and formed NPs with average sizes of 7.0 and 4.2 nm for CdS and ZnS, respectively. A blue shift of UV-Vis absorbance band and higher energy band gap values were observed for both materials in comparison with their bulk counterparts, which is in accordance with the quantum confinement effect. The as-prepared nanomaterials were tested in visible-light driven photocatalytic decomposition of methylene blue (MB). After irradiation for 180 min, the degradation rate of MB with a concentration of 8 × 10−6 mol/L mixed with a photocatalyst (CdS or ZnS, both 10 mg in 100 mL solution of MB) was found to be 72% and 61%, respectively. The CdS NPs showed better photocatalytic activity than ZnS, which could be explained by their lower energy band gap and thus the ability to absorb light more efficiently when activated by visible-light irradiation.

Asymmetric population of momentum distribution by quasi-periodically driving a triangular optical lattice.

Ultracold atoms in periodical-driven optical lattices enable us to investigate novel band structures and explore the topology of the bands. In this work, we investigate the impact of the ramping process of the driving signal and propose a simple but effective method to realize desired asymmetric population in momentum distribution by controlling the initial phase of the driving signal. A quasi-momentum oscillation along the shaking direction in the frame of reference co-moving with the lattice is formed, causing the formation of the mix of ground energy band and first excited band in laboratory frame, within the regime that the driving frequency is far less than the coupling frequency between ground band and higher energy bands. This method avoids the construction of intricate lattices or complex control sequence. With a triangular lattice, we experimentally investigate the influence of the initial phase, frequency, amplitude of the driving signal on the population difference and observe good agreement with our theoretical model. This provides guidance on how to load a driving signal in driven optical lattice experiment and also potentially supplies a useful tool to form a qubit that can be used in quantum computation.

Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle.

The emergence of flat bands and correlated behaviors in "magic angle" twisted bilayer graphene (tBLG) has sparked tremendous interest, though its many aspects are under intense debate. Here we report observation of both superconductivity and the Mott-like insulating state in a tBLG device with a twist angle of ~0.93°, which is smaller than the magic angle by 15%. At an electron concentration of ±5 electrons/moiré unit cell, we observe a narrow resistance peak with an activation energy gap ~0.1 meV. This indicates additional correlated insulating state, and is consistent with theory predicting a high-energy flat band. At doping of ±12 electrons/moiré unit cell we observe resistance peaks arising from the Dirac points in the spectrum. Our results reveal that the "magic" range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG.

Multi-waveband detection of quasi-periodic pulsations in a stellar flare on EK Draconis observed by XMM-Newton

Context. Quasi-periodic pulsations (QPPs) are time variations in the energy emission during a flare that are observed on both the Sun and other stars and thus have the potential to link the physics of solar and stellar flares. Aims. We characterise the QPPs detected in an X-ray flare on the solar analogue, EK Draconis, which was observed by XMM-Newton. Methods. We used wavelet and autocorrelation techniques to identify the QPPs in a detrended version of the flare. We also fitted a model to the flare based on an exponential decay combined with a decaying sinusoid. The flare is examined in multiple energy bands. Results. A statistically significant QPP is observed in the X-ray energy band of 0.2–12.0 keV with a periodicity of 76 ± 2 min. When this energy band is split, a statistically significant QPP is observed in the low-energy band (0.2–1.0 keV) with a periodicity of 73 ± 2 min and in the high-energy band (1.0–12.0 keV) with a periodicity of 82 ± 2 min. When fitting a model to the time series the phases of the signals are also found to be significantly different in the two energy bands (with a difference of 1.8 ± 0.2 rad) and the high-energy band is found to lead the low-energy band. Furthermore, the first peak in the cross-correlation between the detrended residuals of the low- and high-energy bands is offset from zero by more than 3σ (4.1 ± 1.3 min). Both energy bands produce statistically significant regions in the wavelet spectrum, whose periods are consistent with those listed above. However, the peaks are broad in both the wavelet and global power spectra, with the wavelet showing evidence for a drift in period with time, and the difference in period obtained is not significant. The offset in the first peak in the cross-correlation of the detrended residuals of two non-congruent energy bands (0.5−1.0 keV and 4.5−12.0 keV) is found to be even larger (10 ± 2 min). However, the signal-to-noise in the higher of these two energy-bands, covering the range 4.5−12.0 keV, is low. Conclusions. The presence of QPPs similar to those observed on the Sun, and other stars, suggests that the physics of flares on this young solar analogue is similar to the physics of solar flares. It is possible that the differences in the QPPs detected in the two energy bands are seen because each band observes a different plasma structure. However, the phase difference, which differs more significantly between the two energy bands than the period, could also be explained in terms of the Neupert effect. This suggests that QPPs are caused by the modulation of the propagation speeds of charged particles.

An amine linker group modulates luminescent properties in a Rhenium(I) tricarbonyl complex. How can it be applied for ratiometric oxygen sensing?

The UV–Vis absorption spectrum of the rhenium(I) tricarbonyl complex [(NH2-phen)Re(CO)3Br] (ReNN-NH2Br, a deep-orange solid) in solution shows three bands located at 300, 370 and 445 nm. TD-DFT calculations and spectroscopic data indicate that the higher energy band corresponds to a ligand centered transition (LC), while the two lower energy bands have been ascribed to have major ILCT and MLCT character. Excitation at 370 nm leads to two emission bands centered at around 490 nm and 590 nm, which have different nature, 1ILCT and 3MLCT, respectively. Both show a low luminescent quantum yield, especially the lowest energy band. The emission quantum yields in argon-saturated solutions are largely increased, specially for the band at 590 nm. Our results demonstrate that adding the amino group has a non-innocent effect over the luminescent properties of the complex when is compared with those of [(phen)Re(CO)3Br] (ReNNBr). The capacity of these complexes to act as singlet oxygen sensitizers and their application as oxygen sensors were explored. Both complexes, ReNNBr and ReNN-NH2Br, were incorporated in silsesquioxane matrices and tested as ratiometric oxygen sensors using the intrinsic emission of the matrix as an emission internal reference signal. The SSO1-ReNN-NH2Br films was the most sensitive material for this application.

Excitation dynamics of MAPb(I1-xBrx)3 during phase separation by photoirradiation: Evidence of sink, band filling, and Br-Rich phase coarsening

Here, we report the radiative recombination behavior of a binary perovskite, MAPb(I0.2Br0.8)3, during phase separation by investigating photoluminescence (PL) spectrum modulations under different laser irradiation conditions: power density, wavelength (379 and 470 nm), and irradiation time. During laser irradiation, the original PL spectrum was divided into three PL peaks assigned to the 1st I-rich, 2nd I-rich, and Br-rich phases. The observed modulations of the intensity and wavelength of the PL spectrum could be explained by the multiple effects of the charge carrier sink, band filling, and Br-rich phase coarsening. Under a weak laser power density, the observed PL predominantly showed the sink effects of the charge carriers through the excited state potential minimum. As the laser power density or irradiation time increased, new high-energy PL bands appeared owing to the band filling and Br-rich phase formation. With a further increase in the laser power or irradiation time, the PL from the Br-rich phase was intensified, but its PL peak position was red-shifted owing to the quantum size effect from the Br-rich phase coarsening. These variations in PL intensity and charge carrier behavior were carefully studied using time- and space-resolved fluorescence imaging microscopy.

Improved electrical properties of laser annealed In and Ga co-doped ZnO thin films for transparent conducting oxide applications

In this research, dopants with same stoichiometric composition of In and Ga were varied in the range of 1–4 mol% to increase the electrical conductance and optical transmittance. The total sum of 2 mol% of In and Ga co-doped ZnO thin films showed the lowest sheet resistance of 15.9 kΩ/sq. and high transmittance of more than 90% at 380 nm after rapid thermal annealing (RTA) and CO2 laser annealing. Based on scanning electron microscopy images and calculations using the Scherrer formula, the grain sizes were measured and were compared for the increase of In and Ga dopants. The RTA and CO2 laser annealed ZnO thin films co-doped with 2 mol% of In and Ga exhibited a higher energy band gap of 3.29 eV than those of other specimens. The root mean square (RMS) values of the surface roughness were extracted from atomic force microscopy (AFM) images, and the lowest RMS value of 22 nm was obtained for the RTA and CO2 laser annealed ZnO thin films co-doped with 2 mol% of In and Ga. We believe that this increase in the energy band gap is related to the blue shift in the dopant ionization process of In and Ga dopants. And these RTA and CO2 laser annealing can improve the ionization of In and Ga dopants, which is related to the increased energy band gap.

Ionoluminescence investigation of medieval Iranian luster glazed ceramics

Ionoluminescence behavior of some golden glazed ceramic samples from the historical (12th-13th century) cite of Tappeh Ghale, located in the central part of Iran, has been investigated. The required complementary information of the samples, including their elemental compositions and depth profiles, have been provided by means of PIXE and RBS techniques. The results reveal the sensitivity of IL spectra to the layered structure of the luster decorated samples. Indeed, luster layer acts as a mirror-like reflecting surface for the luminescence originating from the underneath layers. Interpretation of the luminescence bands was performed based on the experimental results of PIXE and RBS techniques and the available information in the literature. Some shifts in the peaks’ positions and also appearance of relatively high energy bands were observed.

Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with H.E.S.S.

The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV < E < 100 GeV) γ-ray band, which is continuously monitored with Fermi-LAT. During two periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E > 100 GeV) γ-ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8.7σ significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 ± 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r ≳ 1.7 × 1017 cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279.

Flat bands in twisted double bilayer graphene

Flat bands with extremely narrow bandwidths on the order of a few millielectron volts can appear in twisted multilayer graphene systems for appropriate system parameters. Here we investigate the electronic structure of a twisted bi-bilayer graphene, or twisted double bilayer graphene, to find the parameter space where isolated flat bands can emerge as a function of twist angle, vertical pressure, and interlayer potential differences. We find that in twisted bi-bilayer graphene the bandwidth is generally flatter than in twisted bilayer graphene by roughly up to a factor of 2 in the same parameter space of twist angle $\ensuremath{\theta}$ and interlayer coupling $\ensuremath{\omega}$, making it in principle simpler to tailor narrow bandwidth flat bands. Application of vertical pressure can enhance the first magic angle in minimal models at $\ensuremath{\theta}\ensuremath{\sim}1.{05}^{\ensuremath{\circ}}$ to larger values of up to $\ensuremath{\theta}\ensuremath{\sim}1.{5}^{\ensuremath{\circ}}$ when $P\ensuremath{\sim}2.5$ GPa, where $\ensuremath{\theta}\ensuremath{\propto}\ensuremath{\omega}/{\ensuremath{\upsilon}}_{F}$. Narrow bandwidths are expected in bi-bilayers for a continuous range of small twist angles, i.e., without magic angles, when intrinsic bilayer gaps open by electric fields, or due to remote hopping terms. We find that moderate vertical electric fields can contribute in lifting the degeneracy of the low-energy flat bands by enhancing the primary gap near the Dirac point and the secondary gap with the higher energy bands. Distinct valley Chern bands are expected near ${0}^{\ensuremath{\circ}}$ or ${180}^{\ensuremath{\circ}}$ alignments.

Effect of chronic toxicity of the crystalline forms of TiO2 nanoparticles on the physiological parameters of Daphnia magna with a focus on index correlation analysis

The widespread use of titanium dioxide nanoparticles (NPs) and their inevitable release into aquatic environments have caused great concerns about their ecotoxicity. However, the chronic toxicity to TiO2 NPs of aquatic organisms has not been fully understood. In particular, research is lacking on the influence of the crystalline forms of TiO2 NPs on their mechanisms of toxicity. This study investigated the chronic toxicity (i.e., 21-day toxicity tests) of 5 types of TiO2 NPs with various percentages of crystalline forms on Daphnia magna. Results revealed that the crystalline form composed of 80% anatase and 20% rutile (i.e., the M1 form) had the highest energy band gap (i.e., Eg, the energy interval between the valence band edge and the conduction band edge) and caused maximal D. magna mortality compared with other crystalline forms. The crystalline form comprising 100% rutile (i.e., the R–S form) had the lowest Eg and exhibited a minimal effect on the physiological parameters of D. magna. Moreover, in a suitable environment without TiO2 NPs, D. magna progenies could recover to a normal physiological level (e.g., the mortalities of D. magna progenies were lower than those of parental D. magna that were exposed to TiO2 NPs at a concentration of 0.5 mg/L). Correlation analysis revealed that the body length, time of first brood, and number of neonates in the first brood of D. magna were negatively correlated with titanium accumulation in vivo. Furthermore, the indices of Ti accumulation and the product of Eg and Ti accumulation (i.e., Eg × Ti accumulation) were positively correlated (p < 0.05) with D. magna mortality, thus indicating that crystalline forms with a high Eg may cause severe toxicity to aquatic organisms at the same TiO2 bioaccumulation level.

Lattice dynamics of thermoelectric palladium sulfide

Highly efficient thermoelectric materials always have low thermal conductivities. Their phonon spectrum information is essential for understanding the procedure of thermal transport on thermoelectrics. Recently, palladium sulfide was found to be a potential thermoelectric material. However, the high thermal conductivity limits its thermoelectric performance and technological applications. Here, the phonon dispersion and phonon density of state in PdS are presented by using the first-principles theory. The phonon modes are assigned and compared with experiments. The evolution of optical modes with pressure is studied by using Raman spectroscopy. The low-energy and high-energy phonon bands are related to the vibrations of the heavy atom and the light atom, respectively. By combining Raman scattering and X-ray diffraction measurements, we obtain the mode-Grüneisen parameters for the detected phonon modes. The small mode-Grüneisen parameters indicate a weak anharmonicity in this material. This offers an explanation for its high thermal conductivity. The evolution of linewidths with pressure accounts for the decrease of the thermal conductivity upon compression.

Multi-arm ionic liquid crystals formed by pyridine-mesophase and copper phthalocyanine

Phthalocyanine emerged as a promising molecular component for photoreceptors because of their high extinction coefficients, stability, and energy band gaps well-matched to the incident solar spectrum. The cavity in the center can be occupied by dozens of cation types to form metallo-phthalocyanines which show a number of special properties such as electrical, optical, non-linear optical and opto-electronic. A kind of novel multi-arm ionic liquid crystalline materials combined the characteristics of liquid crystals with phthalocyanine were prepared using copper phthalocyanine as a matrix, [1,1′-biphenyl]-4,4′-diyl diisonicotinate or cyclohexane-1,4-diyl diisonicotinate as a mesogen, and different ions (B-SO3−, C-SO3−, H2PO4− and BF4−) as counterions. The mesomorphic properties of these ionic liquid crystals were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction measurements. The copper phthalocyanine-based multi-arm ionic liquid crystals showed excellent electrical conductivity (the optimum value of conductivity can reach 0.0248 S/cm) because of their ionic channels and π-π stacking structure. This materials might provide a promising application prospect for electronic or optoelectronic applications.

Elucidation of the Structure and Vibrational Spectroscopy of Synthetic Metaschoepite and Its Dehydration Product.

We confirm that synthetic uranyl hydroxide hydrate metaschoepite [(UO)24O(OH)6]·5H2O is unstable against dehydration under dry conditions, and we present a structural and vibrational spectroscopic study of synthetic metaschoepite and its ambient temperature dehydration product. Complementary structural (X-ray diffraction and neutron diffraction) and vibrational spectroscopic techniques (Raman spectroscopy, infrared spectroscopy, and inelastic neutron scattering) are used to probe different components of these species. Analysis of the dehydration product suggests that it contains both pentagonally coordinated and hexagonally coordinated uranyl ions, necessitating that some uranyl ions undergo a coordination change during the dehydration of pentagonally coordinated metaschoepite. Vibrational spectra of metaschoepite and its dehydration product are interpreted with power spectra generated from ab initio molecular dynamics trajectories, allowing assignment of all major features. We identify the uranyl symmetric stretching modes of the four distinct uranyl ions in synthetic metaschoepite and clarify the assignment of lower energy Raman modes in both structures. The coanalysis of experimental and computational data reveals a strong coupling between the uranyl stretching modes and hydroxide bending modes in the anhydrous structure, leading to the presence of several high-energy combination bands in the inelastic neutron scattering data.

Evolutions of geometry and electronic state introduced by oxygen vacancy for CaMnO3 compound

Abstract The cell structures, locally micro-structures, combinations, electronic states as well as carrier transports induced by Oxygen vacancy for the CaMnO3 compound have been systematically investigated by pseudo-potential plane wave functions within the framework of density functional theory calculational method. The results reveal that the Oxygen vacant CaMnO2.75 has larger formation enthalpy than that of the intrinsic CaMnO3 and the Oxygen vacancy formation energy of CaMnO3 is as large as 7.10 eV. The Oxygen vacant CaMnO2.75 is harder to form than the intrinsic CaMnO3. The cubical orthorhombic structure tends to be rhombohedral. The lattice parameters a, b and c decrease simultaneously. The α and γ shrinks, the β increases. The lattice shrinkage induced by oxygen vacancy is anisotropic. The MnO6 octahedrons is twisted and it is shrinked along c and expanded along a. The bond strengths of Mn-O are all enhanced. There are six energy bands and the band gap is narrowed, the Fermi level is heightened and the electrons tend to occupy high energy bands. At the same time, the work function of electrons is lowered from 4.69872 eV to 4.00048 eV. The conductivity should be enhanced for Oxygen vacant CaMnO2.75, the O p and Mn d state electrons contribute most to the upper valance bands as well as the lower conduction bands, they jointly realize the conduction process.

A Search for Pulsed Very High-energy Gamma-Rays from 13 Young Pulsars in Archival VERITAS Data

Abstract We conduct a search for periodic emission in the very high-energy (VHE) gamma-ray band (E &gt; 100 GeV) from a total of 13 pulsars in an archival VERITAS data set with a total exposure of over 450 hr. The set of pulsars includes many of the brightest young gamma-ray pulsars visible in the Northern Hemisphere. The data analysis resulted in nondetections of pulsed VHE gamma-rays from each pulsar. Upper limits on a potential VHE gamma-ray flux are derived at the 95% confidence level above three energy thresholds using two methods. These are the first such searches for pulsed VHE emission from each of the pulsars, and the obtained limits constrain a possible flux component manifesting at VHEs as is seen for the Crab pulsar.

Pseudo Landau level representation of twisted bilayer graphene: Band topology and implications on the correlated insulating phase

We propose that the electronic structure of twisted bilayer graphene (TBG) can be understood as Dirac fermions coupled with opposite pseudo magnetic fields generated by the moir\'e pattern. The two low-energy flat bands from each monolayer valley originate from the two zeroth pseudo Landau levels of Dirac fermions under such opposite effective magnetic fields, which have opposite sublattice polarizations and carry opposite Chern numbers $\pm1$, giving rise to helical edge states in the gaps below and above the low-energy bulk bands near the first magic angle. We argue that small Coulomb interactions would split the eight-fold degeneracy (including valley and physical spin) of these zeroth pseudo Landau levels, and may lead to insulating phases with non-vanishing Chern numbers at integer fillings. Besides, we show that all the high-energy bands below or above the flat bands are also topologically nontrivial in the sense that for each valley the sum of their Berry phases is quantized as $\pm\pi$. Such quantized Berry phases give rise to nearly flat edge states, which are dependent on truncations on the moir\'e length scale. Our work provides a complete and clear picture for the electronic structure and topological properties of TBG, and has significant implications on the natrue of the correlated insulating phase observed in experiments.

Unveiling the origin of the gamma-ray emission in NGC 1068 with the Cherenkov Telescope Array

Several observations are revealing the widespread occurrence of mildly relativistic wide-angle AGN winds strongly interacting with the gas of their host galaxy. Such winds are potential cosmic-ray accelerators, as supported by gamma-ray observations of the nearby Seyfert galaxy NGC 1068 with the Fermi gamma-ray space telescope. The non-thermal emission produced by relativistic particles accelerated by the AGN-driven wind observed in the circum-nuclear molecular disk of such galaxy is invoked to produce the gamma-ray spectrum. The AGN wind model predicts a hard spectrum that extend in the very high energy band which differs significantly from those corresponding to other models discussed in the literature, like starburst or AGN jet. We present dedicated simulations of observations through the Cherenkov Telescope Array (CTA), the next-generation ground based gamma-ray observatory, of the very high energy spectrum of the Seyfert galaxy NGC 1068 assuming the AGN wind and the AGN jet models. We demonstrate that, considering 50 hours of observations, CTA can be effectively used to constrain the two different emission models, providing important insight into the physics governing the acceleration of particles in non-relativistic AGN-driven outflows. This analysis strongly motivates observations of Seyfert and starburst galaxies with CTA in order to test source population models of the extragalactic gamma-ray and neutrino backgrounds.

Hund’s metal regimes and orbital selective Mott transitions in three band systems

We analyze the electronic properties of interacting crystal field split three band systems. Using a rotationally invariant slave boson approach we analyze the behavior of the electronic mass renormalization as a function of the intralevel repulsion U, the Hund’s coupling J, the crystal field splitting, and the number of electrons per site n. We first focus on the case in which two of the bands are identical and the levels of the third one are shifted by with respect to the former. We find an increasing quasiparticle mass differentiation between the bands, for system away from half-filling (n = 3), as the Hubbard interaction U is increased. This leads to orbital selective Mott transitions where either the higher energy band (for 4 > n > 3) or the lower energy degenerate bands (2 < n < 3) become insulating for U larger than a critical interaction . Away from the half-filled case there is a wide range of parameters for where the system presents a Hund’s metal phase with the physics dominated by the local high spin multiplets. Finally, we study the fate of the n = 2 Hund’s metal as the energy splitting between orbitals is increased for different possible crystal distortions. We find a strong sensitivity of the Hund’s metal regime to crystal fields due to the opposing effects of J and the crystal field splittings on the charge distribution between the bands.