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The heterostructure of electrode materials can improve conductivity and ion transport efficiency, thereby enhanced capacitance performance. In this study, we prepared FeMn-LDH by a hydrothermal method and then obtained FeMn-LDH/Ni(OH)2 with a flower-like heterostructure by electrodeposition. This unique heterostructure greatly improves the electrochemical properties of the electrode material, which exhibits a specific capacitance of 2380.5 F g−1 at a current density of 1 A g−1, much higher than that of FeMn-LDH (1109.5 F g−1). Even at a current density of 20 A g−1, the specific capacitance of FeMn-LDH/Ni(OH)2 can still reach 1660 F g−1 with a capacitance retention of 69.9%, which is better than that of FeMn-LDH (46.2%). We then assembled FeMn-LDH/Ni(OH)2 with activated carbon (AC) to form a capacitor. The excellent energy density (49.7 Wh kg−1) and power density (750 W kg−1) proves the potential application of FeMn-LDH/Ni(OH)2. The cycling stability of capacitors is remarkably good, after 10000 cycles, its capacitance still remains 79%. Furthermore, we conducted energy band and density of states (DOS) calculations for FeMn-LDH and FeMn-LDH/Ni(OH)2. The results indicated that the inclusion of Ni(OH)2 enhanced the conductivity of the FeMn-LDH/Ni(OH)2 materials by boosting the transmission of electrons near the Fermi energy level. [ABSTRACT FROM AUTHOR]

Tunable electromagnetically induced transparency-like (EIT-like) metamaterials exhibit extremely high modulation depth and sensitivity, and are widely applied in sensors, modulators and filters. However, frequency shift may occur in the process of regulation, and this law has not been discovered yet. In this work, we reveal the law of frequency shift in tunable EIT-like metamaterials. Based on bright-dark coupling mode and bright-bright coupling mode, two EIT-like metamaterials with simple structures are proposed. The transmission amplitude and frequency of EIT-like effect can be dynamically controlled by tuning the Fermi level of graphene. The law reveals that the frequency of EIT-like effect shifts only when the damping rates of both coupling modes change and the change of one damping rate cannot shift the EIT-like effect. The conclusion can be verified by two-particle model. Due to the universality in tunable EIT-like metamaterials, the law can reduce the blindness of building models in metamaterials and improve the efficiency of structural design. Our work shows great practical prospect in terahertz modulators, optical switches and buffers. [ABSTRACT FROM AUTHOR]

In this paper, we propose a tunable metal-graphene hybrid metamaterial modulator based on the electromagnetically induced transparency (EIT) effect, which can be applied in the terahertz modulation field. The device consists of a U-shaped sliver strip and a rectangular sliver ring. The proposed structure is coupled by bright-bright EIT mode to generate a narrow-band electromagnetically induced transparent window. In the modulation process, the transparent window only changes in amplitude, keeping the resonant frequency constant and improving the device's resistance to interference. Active tunability is achieved by adjusting the bias voltage to alter the Fermi level of the graphene film layer, thereby facilitating modulation performance adjustment. The transparent window has a narrow bandwidth of 0.053 THz, with the transparent peak located at 0.773 THz. The maximum modulation depth of the proposed device is 74.1% and the maximum positive group delay in the transparent window can reach 0.01 ns. The designed structure has the advantages of terahertz modulation and slow light field due to its narrow-band tunability. This work provides a potential solution for electromagnetic wave control for 6G wireless communication. [ABSTRACT FROM AUTHOR]

In this study CoZrMnSb, a quaternary Heusler alloy has been explored utilizing the density functional theory based simulation package WIEN2k. The structural analysis exhibits an X1-type structure with a relaxed lattice constant of 6.27 Å in ferromagnetic phase. The band structure calculations show its half-metallic nature with full spin polarization states around the Fermi level at 0.56 eV energy. In addition, the magnetic moment is calculated to be 1.0 μB, which is in accordance with the Slater Pauling rule (Mtot = (Ztot–24) μB). The study shows the d-d hybridization of the transition metals Co, Zr, and Mn elements. Further, optoelectronic performances in terms of dielectric function, reflectivity, energy loss function, absorption coefficient have been determined for a range of photon energy up to12 eV (ultraviolet region). In optoelectronic applications, absorption of this material in visible light enhances its significance. The thermoelectric properties with chemical potential and thermodynamic properties in the pressure range of 0–40 GPa and temperature range of 0–1200 K have been analysed. Specific heat capacity and Debye temperature authenticate similar metallic behaviour of CoZrMnSb alloy at temperature versus pressure variations. At room temperature, the chemical potential study suggests high figure of merit ~ 0.9, which makes it a potential thermoelectric material. The suggested material has a high Seebeck coefficient and low thermal conductivity, making it a better match for waste heat recovery and spintronic applications. [ABSTRACT FROM AUTHOR]

Recently, a three dimensional metal-organic framework (MOF) based on Dy(III) and the L-tartrate ligand was experimentally shown to exhibit a spin polarization (SP) power of 100% at room temperature. The material's spin filtering ability was ascribed to the chiral-induced spin selectivity (CISS) effect. In this work, we computationally characterize the electronic structure of this MOF, revealing that the high SP of the material is linked to the asymmetric arrangement, around the Fermi level, of the alpha- and beta-spin electron states arising from the 4f-states of the lanthanide Dy atom, which results in two different conduction channels (band gaps) for each spin state. Based on the understanding gathered in this work, we propose that the substitution of the hydroxyl groups of the ligand by mercaptan groups should boost the electrical conductivity, while retaining the spin filtering power of the material. Recently ideal spin filtering ability was demonstrated in the Dy-L-Tar metal-organic framework. In this work the authors show that this unusual effect emerges from the asymmetric display of alpha and beta spin states around the Fermi level, composed of the f states of the lanthanide. [ABSTRACT FROM AUTHOR]

Silicon nanostructures have been prepared on Si wafer using electrochemical etching process. The transformation of aluminum/nanostructured Si junction from Schottky to Ohmic nature has been observed by varying the annealing temperature. This phenomenon has been explained by the temperature dependent shifting of energy levels of defects states instrumental in trapping charges within the forbidden band gap of Si nanostructures. The Aluminum (Al)/nano-Si junction shows asymmetric nature at room temperature and then changes to ohmic at moderate annealing temperature. Finally, at high temperature the junction becomes rectifying in nature. This transition has been explained on the basis of Fermi level pinning due to the modification of distribution of the non-stoichiometric silicon oxide related defect states present at the nanocrystalline Si core-oxide shell interface. [ABSTRACT FROM AUTHOR]

A graphene-coated uniaxial chiral cylindrical waveguide is proposed. Correspondingly, the characteristic equation is derived using appropriate boundary conditions. The effect of chemical potential and chiral parameters is analyzed on propagation modes and energy flux. The characteristics of the hybrid propagation mode in the graphene-coated uniaxial chiral waveguide are more effective than in the dielectric-coated case. The dependence of energy flux and corresponding effective mode index on uniaxial chiral parameters and Fermi level of graphene are revealed. The obtained results may find some potential applications in the fabrication and modulation of novel optoelectronic devices for use in defense technology. The accuracy of the presented analysis is validated by comparing the results derived with the published literature. [ABSTRACT FROM AUTHOR]

In this study, a multi-layered and bi-directionally excitable plasmon-induced transparency (PIT) device with multiple graphene layers was designed. The PIT window was regulated by controlling the Fermi level of graphene, resulting in an increase in the resonance frequency and dip depth of the PIT transmission valleys with an increase in the Fermi level. Theoretical investigations were then conducted. Subsequently, the influence of interlayer distance, individual component size, and relative positioning of graphene on the performance of PIT was studied. When employed as a biosensor, it could only be utilized under x-polarized TM waves, exhibiting a maximum sensitivity of 8.2THz/RIU. As an optical switch, it exhibited the highest modulation depth of 89.7% at 9.04THz under x-polarized waves, and a maximum modulation depth of 94.6% at 2.8THz under y-polarized waves. This theoretically designed PIT device can have potential applications in both sensors and optical switches. [ABSTRACT FROM AUTHOR]

Crystal phase engineering was applied for BiVO4 via the introduction of N-doped CQDs (NCDs), in which the phase of BiVO4 was converted from monoclinic phase to tetragonal phase, generating a self-heterostructure. The intense heterostructure between NCDs and BiVO4 via strong electronic interaction, confirmed by the conversion of crystal phase and XPS results, led to the promoted separation and migration ability of photoinduced carriers. Moreover, the varied band structure (more negative Fermi level) of BiVO4 after the introduction of NCDs and the up-conversion luminescent property of CQDs led to the vast generation of O2−, which was confirmed to play a significant role during RhB photodegradation. However, there existed an optimal introducing amount of NCDs, confirmed to be 30 mg, which revealed 100% photodegradation efficiency after 180 min illumination. The decrease of photocatalytic activity in the condition of excessive NCDs introducing amount was ascribed to the aggregation of these quantum dots or the cover of the active plane of BiVO4 by NCDs. In addition, the photodegradation mechanism exploration revealed that both O2− and photoinduced holes acted as radical species during the photoreduction process, and O2− played more significant role. [ABSTRACT FROM AUTHOR]

This article presents the design of a 2-bit dual-band switchable terahertz absorber using a stacked combination of graphene and vanadium dioxide (VO2) metamaterials. For the first time, the proposed absorber design offers four switchable states by controlling the conductivity of graphene and VO2 metamaterial layers. The lower absorption band is produced by the graphene metamaterial, whereas the upper band is implemented by the VO2 metamaterial pattern. The structure shows two absorption bands (State 11) at 0.745–0.775 THz and 2.3–5.63 THz, when the Fermi graphene level of graphene is 0.2 eV and the VO2 is in the metallic phase. The lower absorption band is turned off, while keeping the upper band (State 01), when the graphene Fermi level is 0 eV and the VO2 layer is in the metallic phase. The upper absorption band is turned off, while preserving the lower absorption band (State 10) by switching the VO2 into the insulator phase and keeping the graphene Fermi level at 0.2 eV. Finally, both of the absorption bands are turned off by setting the graphene Fermi level to 0 eV and switching the VO2 into the insulating phase. Equivalent circuit modelling analysis and full-wave electromagnetic simulations are used to explain the operation principle of the proposed absorber. Very good agreement is obtained between the theoretical analysis and the simulations confirming the presented design principle for the 2-bit switchable absorber. [ABSTRACT FROM AUTHOR]

The electronic structure of Os0.5Pt0.5 bimetallic nanoalloys is studied by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The electronic population on the atoms of these alloys is determined from the obtained experimental data. It is shown that the alloy formation is accompanied by electron transfer from Os atoms to Pt atoms, while the sign and magnitude of the chemical shift are largely determined by the Madelung potential. The shape of the XPS spectra of core lines and the valence band indicate that the local density of states increases on the Os atoms near the Fermi level. Prospects of using the nanoalloys in catalytic reactions are discussed by analyzing the valence d-band parameters. [ABSTRACT FROM AUTHOR]

A continuous quasi-equilibrium phase diagram δ(pO2, T) of a nonstoichiometric oxide La2NiO4 + δ with the layered perovskite-like Ruddlesden–Popper structure is obtained by the method of quasi-equilibrium oxygen release. The thermodynamic parameters are determined as a function of the oxide nonstoichiometry δ. Calculations are carried out within the framework of the localized-electron and itinerant-electron models which are used for description of the defect structure of ferrites and cobaltites, respectively. It is shown that the specific features of the phase diagram can be related to the electronic density of states near the Fermi level. [ABSTRACT FROM AUTHOR]

In this manuscript, an original graphene-based metamaterial perfect absorber (MPA) was suggested and investigated with substituting aluminum with graphene. The proposed structure consists of a gold substrate as a conductive layer, a silicon substrate as a middle insulated layer and the patterned graphene layer as a resonator. The suggested structure, with only one metamaterial layer, has a lot of advantages such as simple implementation, cost-effectiveness, simple design and frequency tunability. The results of the proposed absorber, demonstrate that the absorber can provide absorption close to 100% at the frequencies of 0.56, 0.79, 1.02 and 1.25 THz by 0.9 eV graphene chemical potential (μc). With increasing the thickness of the silicone insulating layer, the absorption peaks number can be increased up to XIII bands. Also, changing the Fermi level can cause an absorption frequency shift. Furthermore, this structure is polarization insensitive and it is tolerating incident angles up to 45°. The recommended absorber is an appropriate candidate for filtering, spectroscopy, imaging and sensing application. [ABSTRACT FROM AUTHOR]

Half-metallic ferromagnetic Heusler alloys attracted much attention in the last few decades due to their significant physical properties as well as its potential applications in spintronic devices. To explore and predict the various physical properties of Co-based Heusler alloy, Co2MnSi (CMS), First principles calculations are of interest and has been used in the present study. Optimized E–V curves represent that CMS alloy is most stable in its magnetic L21 structural phase. The electronic charge density plot represents the ionic bonding along with co-valent character for the compound. DOS and BS calculations shows 100% spin polarization at Fermi level (EF) which confirms the half metallic character of the compound. DOS exhibited the prominent role of Co-3d and Mn-3d electronic states along with Si-2p electronic states. Estimated magnetic moment of Co2MnSi Heusler alloy was found to be ~ 5μB per f. u. which is in line with the Slater-Pauling behaviour. Dynamical stability of Co2MnSi Heusler alloy has also been verified by the phonon dispersion curves which revealed that compound is dynamically stable. Additionally, the physical properties have also been explored as a consequence of SOC and significant changes in electronic and optical properties were observed. The observed significant results of electronic, magnetic, and optical properties of CMS Heusler alloy makes it promising towards potential application in optical and spintronic devices. [ABSTRACT FROM AUTHOR]

The combination of strongly coupled Cooper pairs and weak superconducting fluctuations is an important prerequisite for achieving high-temperature superconductivity. The review is devoted to the implementation of this condition in multiband superconductors, in which strongly coupled pairs in the shallow conduction band (the Fermi level is close to the band edge) coexist with ordinary, weakly fluctuating Cooper pairs formed in the deep band. As a result of the Josephson coupling between condensates in different bands, such a system is characterized by a high critical coherence temperature due to the presence of strongly coupled pairs and the suppression of superconducting fluctuations. This suppression does not require any special preconditions, and is almost total even if the Josephson coupling between the bands is weak. [ABSTRACT FROM AUTHOR]

In this work, iron selenide layers are deposited onto glass and lead substrates to perform as terahertz filters. The layers are deposited by the thermal evaporation technique under a vacuum pressure of 10–5 mbar. Glass/FeSe2 (GFS) and Pb/FeSe2 (PFS) films are structurally, morphologically and electrically characterized. The atomic composition of the GFS films contained excess selenium that reacted with Pb forming a PbSe layer. This layer induced the crystallinity of iron selenide. The preferred crystal structure of FeSe2 was cubic with cell parameters of a = b = c = 3.04 Å and space group P m 3 m . Lead substrates increased the room temperature electrical conductivity of GFS films from of 1.52 × 10 - 5 (Ω cm) - 1 to 6.88 × 10 - 2 (Ω cm) - 1 . Analyses of the electrical conduction mechanism in the temperature range of 25–330 K have shown that coating the films onto Pb substrates shifted the accepter level from 182 to 58 meV, decreased the degree of structural disorder, shorten the average hopping range from 59 to 19 Å and increased the density of localized states near Fermi level by two orders of magnitude. The conductivity of PFS films exhibited degenerate semiconductor characteristics in the temperature range of 120–28 K. This feature is followed by an evidence of exhibiting superconductivity at critical temperatures lower than 24 K. On the other hand the impedance spectroscopy measurements in the driving signal frequency domain of 0.01–1.0 GHz have shown that Pb/FeSe2/Ag interfaces can perform as band filters showing microwave cutoff frequency values reaching 100 GHz at driving signal frequency of 1.0 GHz. These band filters are ideal for 6G technology nominating PFS films for high frequency applications. [ABSTRACT FROM AUTHOR]

The surface spin-polarized states in the electronic structure of Pt(111) and graphene/Pt(111) have been studied in detail using angle-resolved photoelectron spectroscopy and density functional theory calculations. The results obtained show the presence of cone-shaped surface states near the Fermi level in the vicinity of the point of the surface Brillouin zone of platinum for both systems. Theoretical calculations confirm that these states are spin-polarized surface states of Pt(111) single crystal. [ABSTRACT FROM AUTHOR]

Migdal-Eliashberg theory is one of the state-of-the-art methods for describing conventional superconductors from first principles. However, widely used implementations assume a constant density of states around the Fermi level, which hinders a proper description of materials with distinct features in its vicinity. Here, we present an implementation of the Migdal-Eliashberg theory within the EPW code that considers the full electronic structure and accommodates scattering processes beyond the Fermi surface. To significantly reduce computational costs, we introduce a non-uniform sampling scheme along the imaginary axis. We demonstrate the power of our implementation by applying it to the sodalite-like clathrates YH6 and CaH6, and to the covalently-bonded H3S and D3S. Furthermore, we investigate the effect of maximizing the density of states at the Fermi level in doped H3S and BaSiH8 within the full-bandwidth treatment compared to the constant-density-of-states approximation. Our findings highlight the importance of this advanced treatment in such complex materials. Migdal-Eliashberg theory is a method for describing conventional superconductors. Here, the authors present an implementation that goes beyond the widely used constant density of states approximation by accommodating scattering processes beyond the Fermi surface, and they show its importance in two classes of near room temperature superhydrides. [ABSTRACT FROM AUTHOR]

The influence of sintering temperature on the thermoelectric (TE) transport of BiCuSeO is reported in the present work, with an aim to optimize the processing conditions for higher TE transport. BiCuSeO samples were synthesized at four different sintering temperatures, viz., 673 K, 773 K, 873 K, and 973 K. A non-degenerate type of conductivity is observed in all the samples at high temperatures, witnessing the thermal activation of the carriers. The Fermi level was positioned below the valence band maximum, thereby exhibiting a p-type degenerate transport in the entire range of temperature. It was observed that the variations of weighted mobility and power factor were found to have identical trends. The highest power factor was noticed at 554 K with a value of 129 μWm−1 K−2 for the sample sintered at 673 K. [ABSTRACT FROM AUTHOR]

Studies of light-induced demagnetization started with the experiment performed by Beaupaire et al. on Ni. Here, we present theoretical predictions for X-ray induced demagnetization of nickel, with X-ray photon energies tuned to its M 3 and L 3 absorption edges. We show that the specific feature in the density of states in the d-band of Ni, i.e., a sharp peak located just above the Fermi level, strongly influences the change of the predicted magnetic signal, making it stronger than in the previously studied case of X-ray demagnetized cobalt. It impacts also the value of Curie temperature for Ni. We believe that this finding will inspire dedicated experiments investigating magnetic processes in X-ray irradiated nickel and cobalt. [ABSTRACT FROM AUTHOR]

The transport properties of the graphene-based antiferromagnet/insulator/ferromagnet/superconductor junction with noncollinear magnetic moments are theoretically investigated under the Bogoliubov-de Gennes equation. By introducing a mass term into the antiferromagnetic region, the spin-polarized equal-spin Andreev reflection (EAR) can be achieved for all voltages in the subgap region, free from any interference from the opposite-spin Andreev reflection (OAR). The transition from the retro EAR to the specular EAR can be realized by adjusting the Fermi level within the antiferromagnetic region. The perfect EAR can be obtained, suggesting an efficient equal-spin pairing correlation. Furthermore, we note that the EAR exhibits magnetoisotropy with an in-plane ferromagnetic exchange field, which is opposite to the results in a ferromagnet/ferromagnet/superconductor junction. [ABSTRACT FROM AUTHOR]

A theoretical study was conducted to analyze electronic, elastic, and thermodynamic properties and the structural stability of the intermetallic materials Al3Ti1−xZrx for tetragonal-D022 and cubic-L12 structures carried out based on DFT. The findings indicate that the D022 phase has demonstrated more stability than the L12 phase and the possibility of a structural phase transition under pressure effect for concentrations x = 0.25 and x = 0.5. With increasing x concentration, the resulting lattice parameters drop. The density of states at the Fermi level, determines the electronic stability exhibited by these compounds. A pseudo-gap in proximity to the Fermi level implies the establishment of directional covalent bonding. The electronic structures support the phase stability results and show that the bonding in these compounds is more directed. Measurement techniques are employed to determine the number of bonding electrons per atom and the coefficient of electronic-specific heat. Both the mechanical as well as elastic properties of the considered alloys are examined. The findings demonstrate that all explored alloys are brittle, and D022 phase is stiffer than the L12 phase. The thermal characteristics are predicted via the quasi-harmonic Debye model. [ABSTRACT FROM AUTHOR]

The zero band gap of pure graphene is a well-known issue that limits some specific applications of graphene in opto- and microelectronics. This led to several research studies in the so‐called van der Waals composites (known as heterostructures, or heterojunctions), where two monolayers of different materials are stacked and held together by dispersive interactions. In this paper, we introduced and considered a single layer of brucite Mg(OH)2, an overlooked 2D material that can be easily produced by exfoliation (like graphene from graphite), for the creation of the heterojunction. First principles simulations showed that brucite/graphene composites can modify the electronic properties (position of the Dirac cone with respect to the Fermi level and band gap) according to the crystallographic stacking and the presence of point defects. The present work represents then an important step forward in understanding and finding new ways to design two-dimensional materials with tailored electronic and physical properties. [ABSTRACT FROM AUTHOR]

Iron-chalcogenide superconductors display rich phenomena caused by orbital-dependent band shifts and electronic correlations. Additionally, they are potential candidates for topological superconductivity due to the band inversion between the Fe d bands and the chalcogen pz band. Here we present a detailed study of the electronic structure of the nematic superconductors FeSe1−xTex (0 < x < 0.4) using angle-resolved photoemission spectroscopy to understand the role of orbital-dependent band shifts, electronic correlations and the chalcogen band. We assess the changes in the effective masses using a three-band low energy model, and the band renormalization via comparison with DFT band structure calculations. The effective masses decrease for all three-hole bands inside the nematic phase, followed by a strong increase for the band with dxy orbital character. Interestingly, this nearly-flat dxy band becomes more correlated as it shifts towards the Fermi level with increasing Te concentrations and as the second superconducting dome emerges. Our findings suggests that the dxy hole band, which is very sensitive to the chalcogen height, could be involved in promoting an additional pairing channel and increasing the density of states to stabilize the second superconducting dome in FeSe1−xTex. This simultaneous shift of the dxy hole band and enhanced superconductivity is in contrast with FeSe1−xSx. The iron chalcogenide material FeSe1-xTex constitutes an important family of unconventional superconductors but its nematic phase was less explored due to a lack of single crystals. In this study, the authors provide a systematic study of the electronic structure for nematic FeSe1-xTex and observe that as the Te content increases a gradual shift and renormalization of the dxy orbital occurs, concomitant with the enhancement of superconductivity. [ABSTRACT FROM AUTHOR]

A magnetic field parallel to the layers of a double quantum well with conventional semiconductor constituents leads to a relative shift of the conduction band spectra of the constituent layers along the wave vector perpendicular to the field. If the states of the layers are tunnel-coupled, a tunneling gap is formed at the intersection of the single-layer spectra and is shifted upward with increasing field. This leads to striking features in the magnetoresistance caused by intersections of the Fermi level with the edges of the tunneling gap. Similar studies of transformations of the spectrum of the double quantum well in a HgTe/CdHgTe heterosystem, which has a p-type conductivity and HgTe layers with a gapless inverse energy spectrum, are reported in this work. Our experiments and corresponding calculations in the eight-band kp approach indicate that the evolution of the magnetoresistance with the variation of the in-plane field here has a much more complex and diverse character depending qualitatively on the thickness of the layers. [ABSTRACT FROM AUTHOR]

The electronic structure of ultrathin Cs/Bi2Se3 interfaces has been studied by photo electron spectroscopy using synchrotron radiation. The experiments were carried out in situ in ultrahigh vacuum with submonolayer Cs coverages on Bi2Se3 samples. It was found that the adsorption of Cs causes changes in the core level spectra of Bi 4f, Bi 5d, Se 3d. It has been established that Cs atoms are adsorbed predominantly on Bi atoms in the upper surface layer. The states of the valence band were studied for a clean Bi2Se3 surface and for the Cs/Bi2Se3 interface. Near the Fermi level, 2D topological states have been found. Two induced surface states appear in the region of the valence band upon adsorption of Cs. [ABSTRACT FROM AUTHOR]

By methods of electron spectroscopy for chemical analysis and spectroscopy of characteristic losses of electron energy, the electronic structure of barium oxide crystallites doped with other chemical elements, including scandium from scandium-containing phases, was investigated. The physical and physicochemical conditions are formulated, the fulfillment of which allows to form the electronic structure of the scandate cathode with a high level of thermionic emission: the achievement of the minimum ratio of the surface volume concentration of oxygen vacancies and the maximum distance between the top of the valence band and the Fermi level. [ABSTRACT FROM AUTHOR]

Spectral studies of the photoconductivity in the temperature range of T = 5–70 K, as well as studies of the magneto-absorption and magnetotransport at T = 4.2 K, have been performed in a HgTe/CdHgTe heterostructure with a double quantum well under an "optical gate" effect. Studies of magneto-absorption spectra under the controlled optical exposure have made it possible to observe absorption lines caused by both the cyclotron resonances of electrons and holes simultaneously. The coexistence of electrons and holes in the HgTe/CdHgTe double quantum well with a relatively large bandgap (~80 meV) indicates the appearance of a strongly inhomogeneous light-induced distribution of charge carriers in the plane of the structure. Experimental results obtained clearly demonstrate disadvantages of the control of the Fermi level positions in heterostructures with HgTe/CdHgTe quantum wells by means of the optical gate. [ABSTRACT FROM AUTHOR]

Density functional theory is employed to investigate the electronic band structure of tetragonal Fe 2 Ge. The Dirac cone formation is identified in the bulk electronic configuration of Fe 2 Ge near the Fermi energy level, rather than in the surface states as anticipated. The analysis of Dirac bands suggests that tetragonal Fe 2 Ge can be considered as topological crystalline insulator as suggested by Liang Fu et al. in Phys. Rev. B 76, 045302. The Dirac point exhibits quadratic degeneracy at the high symmetry point 'X' for spin-up channel and at 'M' for spin-down channel in the tetragonal Brillouin zone. The effect of lattice strain and spin-orbit coupling on the energy gap opening at the Dirac point as well as the dependency of the exchange-correlation functional are discussed. These current studies will add a new family of alloys to the topological phase in the band insulators. [ABSTRACT FROM AUTHOR]

The electronic structure of UC x (x = 0.9, 1.0, 1.1, 2.0) was studied by means of x-ray absorption spectroscopy (XAS) at the C K edge and measurements in the high energy resolution fluorescence detection (HERFD) mode at the U M 4 and L 3 edges. The full-relativistic density functional theory calculations taking into account the 5 f - 5 f Coulomb interaction U and spin-orbit coupling (DFT+U+SOC) were also performed for UC and UC 2 . While the U L 3 HERFD-XAS spectra of the studied samples reveal little difference, the U M 4 HERFD-XAS spectra show certain sensitivity to the varying carbon content in uranium carbides. The observed gradual changes in the U M 4 HERFD spectra suggest an increase in the C 2p-U 5f charge transfer, which is supported by the orbital population analysis in the DFT+U+SOC calculations, indicating an increase in the U 5f occupancy in UC 2 as compared to that in UC. On the other hand, the density of states at the Fermi level were found to be significantly lower in UC 2 , thus affecting the thermodynamic properties. Both the x-ray spectroscopic data (in particular, the C K XAS measurements) and results of the DFT+U+SOC calculations indicate the importance of taking into account U and SOC for the description of the electronic structure of actinide carbides. [ABSTRACT FROM AUTHOR]

The interaction of tyramine neurotransmitter with silver nano-particle (Ag6) cluster is explored in terms of the molecular structure, electronic properties and NBO analysis of tyramine-AgNPs bio-molecular conjugate. The adsorption mechanism of tyramine onto the Ag6 cluster has been investigated through computing of the electronic and geometrical properties in addition to the adsorption energies in various possible configurations. The magnitude of adsorption energy corresponding to the most favorable tyramine-Ag6 bio-molecular conjugate has been computed to be − 14.36 kcal/mol in the gas phase, which infers a good adsorption of tyramine with AgNPs cluster suggesting the practical applications of tyramine-AgNPs bio-molecular conjugates in bio-sensing, drug delivery, bio-imaging and other applications. Different electronic properties such as the energy gap of HOMO–LUMO, Fermi level and work function have been investigated in detail. Moreover, the effect of aqueous media on adsorption energy and electronic properties of the most favorable tyramine-AgNPs bio-molecular conjugate is investigated in order to understand the impact of the real biological situation. [ABSTRACT FROM AUTHOR]

This work investigates the function of the oxygen partial pressure in photo-induced current measurement of extended defect properties related to the distribution and quantity of defect states in electronic structures. The Fermi level was adjusted by applying a negative gate bias in the TFT structure, and the measurable range of activation energy was extended to < 2.0 eV. Calculations based on density functional theory are used to investigate the changes in defect characteristics and the role of defects at shallow and deep levels as a function of oxygen partial pressure. Device characteristics, such as mobility and threshold voltage shift under a negative gate bias, showed a linear correlation with the ratio of shallow level to deep level defect density. Shallow level and deep level defects are organically related, and both defects must be considered when understanding device characteristics. [ABSTRACT FROM AUTHOR]

We investigate how a change in dimensionality of interstitial electronic states in the Ca2N electride influences its electronic structure and transport properties. Employing the Maximally Localized Wannier Functions (MLWF) approach, we successfully describe the interstitial quasi-atomic states (ISQ) located in non-nuclear Wyckoff positions between Ca atoms. This allowed us to conclude that the electride subsystem is responsible for the formation of a band structure in the vicinity of the Fermi level in all Ca2N phases observed under pressure. Using the obtained MLWF basis, we calculate the electronic and thermal conductivity, along with the Seebeck coefficient, by solving the semi-classical Boltzmann transport equations. The results achieved permit the conclusion that the counterintuitive increase in resistance under pressure observed experimentally is attributed to enhanced localization of interstitial electronic states through electride subspace dimensionality transformations. We also established a substantial anisotropy in the transport properties within the 2D phase and found that the conductivity inside the plane of the electride layers is provided by electrons, while along the direction normal to the layers, holes become the majority carriers. [ABSTRACT FROM AUTHOR]

Recently it was claimed that nitrogen-doped lutetium hydride exhibited a near-ambient superconducting transition with a temperature of 294 K at a pressure of only 10 kbar, this pressure being several orders of magnitude lower than previously demonstrated for hydrides under pressure. In this paper, we investigate within DFT + U the electronic structure of both parent lutetium hydride LuH3 and nitrogen doped lutetium hydride LuH2.75N0.25. We calculated corresponding bands, density of states and Fermi surfaces with and without spin-orbit coupling (SOC). It is shown that in the stoichiometric system the Lu-5 states cross the Fermi level while the H- states make almost no contribution at the Fermi level. However, with nitrogen doping, the N‑ states enter the Fermi level in large quantities and bring together a significant contribution from the H‑ states. The presence of N- and H- states at the Fermi level in a doped compound can facilitate the emergence of superconductivity. Surprisingly, SOC splits quite significantly (0.1–0.25 eV) nitrogen bands in LuH2.75N0.25 just below the Fermi level. For instance, nitrogen doping almost doubles the value of DOS at the Fermi level. Simple BCS analysis shows that the nitrogen doping of LuH3 can provide more than 100 K and even increase it with further hole doping. [ABSTRACT FROM AUTHOR]

We show the importance of using a thermodynamically consistent flux discretization when describing drift–diffusion processes within light emitting diode simulations. Using the classical Scharfetter–Gummel scheme with Fermi–Dirac statistics is an example of such an inconsistent scheme. In this case, for an (In,Ga)N multi quantum well device, the Fermi levels show an unphysical hump within the quantum well regions. This result originates from neglecting diffusion enhancement associated with Fermi–Dirac statistics in the numerical flux approximation. For a thermodynamically consistent scheme, such as the SEDAN scheme, the humps in the Fermi levels disappear. We show that thermodynamic inconsistency has far reaching implications on the current–voltage curves and recombination rates. [ABSTRACT FROM AUTHOR]

On-surface synthesis is of importance to fabricate low dimensional carbon-based nanomaterials with atomic precision. Here, we synthesize nitrogen-doped nanographene with an [18]annulene pore and its dimer through sequential reactions of debromination, aryl–aryl coupling, cyclodehydrogenation and C–N coupling on Ag(111) from 3,12-dibromo-7,8-diaza[5]helicene. The inner structures of the products were characterized with scanning tunneling microscopy with a CO terminated tip at low temperature. Furthermore, the first four unoccupied electronic states of the nanographene were investigated with a combination of scanning tunneling spectroscopy and theoretical calculations. Except for the LUMO + 2 state observed at +1.3 V, the electronic states at 500 mV, 750 mV and 1.9 V were attributed to the superatom molecular orbitals at the [18]annulene pore, which were significantly shifted towards the Fermi level due to the hybridization with the confined surface state. On-surface synthesis is a key tool to access low dimensional carbon-based nanomaterials with atomic precision. Here, the authors synthesize a nitrogen-doped nanographene structure with an [18]annulene pore on Ag(111) through sequential debromination, aryl–aryl coupling, cyclodehydrogenation and C–N coupling reactions from a 3,12-dibromo-7,8-diaza[5]helicene precursor. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the low-threshold optical bistable absorption in an asymmetrical one-dimensional photonic crystal structure (1D-PhC) containing a Weyl semimetal (WSM) defect layer. Dirven by the strong third-order nonlinear effect of the WSM and the field enhancement of the defect mode, low-threshold bistable absorption is achieved in the terahertz band. After optimizing the parameters, the rising threshold intensity is 83.7817 MW/m2 and the falling threshold intensity is 49.39 MW/m2, which are lower than the threshold intensities of bistable absorption in the reported works. Meanwhile, we discuss the effects of Fermi level of WSM, incident angle, and the numbers of periods of the left and right 1D-PhCs on the bistable absorption. Our work would facilitate the design of high-performance all-optical switches, all-optical logics, and optical absorbers. [ABSTRACT FROM AUTHOR]

We investigate the parameter regimes favourable for the emergence of plasmons in isotropic, anisotropic, and band-mass symmetric and asymmetric Luttinger semimetals (LSMs). An LSM harbours a quadratic band-crossing point (QBCP) in its bandstructure, where the upper and lower branches of dispersion are doubly degenerate. While a nonzero temperature (T) can excite particle-hole pairs about the Fermi level due to thermal effects (even at zero doping), a finite doping (μ ) sets the Fermi level away from the QBCP at any T, leading to a finite Fermi surface (rather than a Fermi point). Both these conditions naturally give rise to a finite density of states. A nonzero value of T or μ is thus a necessary condition for a plasmon to exist, as otherwise the zero density of states at the QBCP can never lead to the appearance of this collective mode. In addition to T and μ , we consider the effects of all possible parameters like cubic anisotropy, band-mass asymmetry, and a material-dependent variable X that is proportional to the mass (of the quasiparticle) and the number of fermion flavours. We implement a random-phase-approximation to compute the quasiparticle decay rate τ - 1 (also known as the inelastic scattering rate) resulting from screened Coulomb interactions. A well-defined sharp peak in the profile of τ - 1 signals the appearance of a plasmon. From our results, we conclude that X turns out to be a crucial tuning parameter, as higher values of X assist in the emergence of plasmons. On the other hand, the features are broadly insensitive to cubic anisotropy and band-mass asymmetry. [ABSTRACT FROM AUTHOR]

Time-resolved ARPES gives access to the band structure and ultrafast dynamics of excited electronic states in solids. The orbital character of the bands close to the Fermi level is essential to understand the origin of several exotic phenomena in quantum materials. By performing polarization-dependent time- and angle-resolved photoemission spectroscopy and by analyzing the photoelectron yield for two different crystal orientations, we identify the orbital character of bands below and above the chemical potential for the Dirac semimetal BaNiS 2 . Our results illustrate how the control and understanding of matrix elements' effects in time-resolved photoemission spectroscopy can be a powerful tool for the study of quantum materials. [ABSTRACT FROM AUTHOR]

Light-induced desorption of Rb atoms from a ferrimagnetic Fe 3 O 4 (001) surface was studied using a spin-selective optical method, which provides information on the spin polarization, velocity distribution, and amount of the desorbed atoms. The results showed that the intensity of the desorption of Rb from Fe 3 O 4 (001) induced by ultraviolet (UV) light irradiation was smaller than the detection limit at coverages lower than the threshold coverage at which the desorption rate began to increase. Moreover, the average magnetic quantum number of the desorbed atoms was smaller than that of electrons at the Fermi level of the Fe 3 O 4 (001) surface. These indicate that the light-induced desorption of Rb from an Fe 3 O 4 (001) surface occurs only in the high-coverage region in which the desorbing atoms are not in contact with the Fe 3 O 4 surface, and that the desorption does not involve spin transfer. [ABSTRACT FROM AUTHOR]

DFT calculations were used to study the quantum capacitance of pure, B/Al/Si/N/P-doped, and defective γ-graphyne. Due to the direct relationship between capacitance and electronic states around the Fermi level, structures' electronic properties were evaluated by DOS plots. The results of integrated specific quantum capacitance in the range of water stability potential show an improvement of capacity in each p and n-type doping. The calculated cohesive energies of doped structures reflect the stability enhancement. Also, the stability/capacitance of single and double vacancies in two distinct positions (sp and sp2) were examined. The results illustrate stability retention and quantum capacitance improvement of these defective structures. Among the doped structures, the maximum quantum capacitance is 2251.10 F/gr belonging to the aluminum doped structure (in the sp position). For the defective structures, the maximum quantum capacitance is 4221.69 F/gr belonging to removing two sp carbon atoms. These quantum capacitances significantly improved compared to the pristine structure (1216.87 F/gr) and many other structures. These stunning results can contribute to the design of appropriate structures as electrode materials for high-efficiency supercapacitors. [ABSTRACT FROM AUTHOR]

In this study, we employed thermal evaporation under vacuum conditions to introduce copper dopants into amorphous InSe thin films. Our objective was to scrutinize the effects of varied copper doping concentrations on the structural, compositional, electrical, and photoelectrical properties of the films. Our observations indicated that copper doping did not induce discernible alterations in the amorphous morphology of the InSe films, yet it yielded notable enhancements in the material's atomic stoichiometry. Notably, films subjected to both pristine conditions and 0.09 at. % copper doping exhibited extrinsic n-type conductivity behavior, while those doped with 0.42 at. % copper displayed a transition to p-type conductivity. Furthermore, our investigation encompassed electrical conductivity measurements conducted over a temperature range spanning from 100 to 320 K, elucidating the dominance of thermal excitation mechanisms at higher temperatures, and the prevalence of variable range hopping (VRH) processes at lower temperatures. The magnitude of copper dopants in the InSe matrix exerted discernible influence over impurity kinetics and VRH parameters, encompassing factors such as the degree of disorder, density of states proximate to the Fermi level, and average hopping distance. Additionally, our photoelectrical assessments unveiled that a nominal concentration of copper doping (0.09 at. %) yielded a remarkable augmentation of over 70% in the photoconductivity of the InSe films, underscoring its potential suitability for optoelectronic applications. [ABSTRACT FROM AUTHOR]

To study the role of the emitter and collector electrode materials in Ferroelectric Tunnel Junctions (FTJs), an in-depth theoretical investigation of 4 single-barrier FTJs (Pt/BTO/SRO, Pt/BTO/Pt, SRO/BTO/SRO, and SRO/BTO/Pt) is reported. Compared with all known conduction mechanisms in FTJ, it is found that direct quantum tunneling provides the most predominant contribution to the current density in the above systems for the bias range of 0–1.2 V. The lowering of the barrier height and asymmetry in the barrier profile which determines the tunneling current is controlled by the potential drop in the accumulation region in the emitter and the depletion region in the collector which depends on the ratio of screening length, δ , to permittivity, ϵ , of the corresponding electrodes. The tunneling electro-resistance ratio (TER) is found to have significant values for bias potential V > P δ 1 ϵ 1 + δ 2 ϵ 2 wherein the screening charge density σ s , and the net charge density in the barrier layer σ s - P remain negative resulting in the pull-down of the barrier toward the Fermi level and producing a negative slope in the barrier to increase the tunneling current. Among the studied systems, Pt/BTO/SRO provides the highest TER. Specifically, Pt/24Ǻ BTO/SRO system with an active device length of 5.6 nm is found to have a current density of 2.54 × 104A/cm2 and 1.28 × 102A/cm2 in the ON and OFF state and a TER of nearly 20,000% at the bias of 0.71 V confirming to the necessary conditions of efficient application in memory devices. [ABSTRACT FROM AUTHOR]

An ultra-low pump intensity and high photon flux have been long pursuits of high harmonic generation (HHG) in solids. However, there is lack of a criterion to identify a pristine solid material exhibiting such characteristics. Here, we report systematic investigation into HHG from a cadmium telluride (CdTe) bulk crystal with a flat band dispersion near the Fermi level which leads to a large density of states. The measured pump intensity for the 31st harmonics (229 nm) is only 75 GW/cm2, one order of magnitude lower than that of other pristine crystals including two-dimensional materials reported so far. A comparative measurement shows CdTe has two-to-three orders of magnitude stronger HHG than silicon does, and high HHG yields in the ultraviolet region compared to GaSe. A high photon flux of ~ 6 × 1012 photons/s (5th−8th) with a robust long-time sustainability is obtained. This work offers a route towards compact vacuum ultraviolet laser sources. Efficient high harmonic generation (HHG) in solids is instrumental for devising applications in XUV spectroscopy, attosecond science and coherent diffraction imaging. Through a systematic experimental comparison, the authors individuate CdTe as the ideal candidate for generating high harmonics with ultra-low pump intensity and high photon flux. [ABSTRACT FROM AUTHOR]

This work investigates the function of the oxygen partial pressure in photo-induced current measurement of extended defect properties related to the distribution and quantity of defect states in electronic structures. The Fermi level was adjusted by applying a negative gate bias in the TFT structure, and the measurable range of activation energy was extended to < 2.0 eV. Calculations based on density functional theory are used to investigate the changes in defect characteristics and the role of defects at shallow and deep levels as a function of oxygen partial pressure. Device characteristics, such as mobility and threshold voltage shift under a negative gate bias, showed a linear correlation with the ratio of shallow level to deep level defect density. Shallow level and deep level defects are organically related, and both defects must be considered when understanding device characteristics. [ABSTRACT FROM AUTHOR]

Recent advances in the precise preparation, process, and manipulation of multilayer graphene quantum dots make it possible to engineer effectively their energy gaps (Δε) by tuning the stacking thickness, interlayer twist angle, quantum dot size, and external electric field strength. The coupling mechanism among these operations is however ambiguous. Using first-principles calculations, the Δε variations of multilayer graphene quantum dots are studied at a varying stacking thickness, twist angle, and field strength. The combination of these diverse operations not only widens the Δε windows but also generates quasi-continuous Δε variations. Every operation may alter the interlayer coupling strength, which becomes more sensitive under the combination of two or more operations, resulting from the different responses of the Kohn–Sham orbitals around the Fermi level against the operations. Analysis of the vertical polarizability reveals that interlayer charge transfer ability is tuned by the operations, which accounts for the variations in interlayer coupling and consequently in Δε. Understanding the coupling mechanism is helpful for the precise control over the band gaps of the multilayer graphene quantum dots in their optoelectronic applications. [ABSTRACT FROM AUTHOR]

The development of photocatalysts with efficient charge separation and transferring is essential for efficient photocatalytic H2 generation. Here, we have constructed Sn2+ and Sn4+ double-doped ZnIn2S4 (Sn2+/Sn4+-ZnIn2S4) catalyst by using a one-step solvothermal method. Sn4+ replaces the Zn ion and creates an additional energy state near the Fermi level, which act as electron accepters. The receptor states boost the metallic conductive properties of ZnIn2S4 and reduce the recombination of photo-induced electrons and holes. The Sn2+ combines with edge S atoms of ZnIn2S4 due to the large ionic radius, which modulates the band gap structure. Both experimental results and theoretical calculations show that the Sn2+and Sn4+ ion double doping increases charge density and narrows the bandgap for light capture. Therefore, the Sn2+/Sn4+-ZnIn2S4 catalyst shows an excellent catalytic activity for hydrogen production (2.48 mmol·g−1·h−1), and it is 35.4 times that of the original ZnIn2S4 (0.07 mmol⋅g−1⋅h−1). This work opens a promising path for developing highly efficient photocatalysts for solar photocatalytic H2 generation. [ABSTRACT FROM AUTHOR]

Identifying the magnetic state of materials is of great interest in a wide range of applications, but direct identification is not always straightforward due to limitations in neutron scattering experiments. In this work, we present a machine-learning approach using decision-tree algorithms to identify magnetism from the spin-integrated excitation spectrum, such as the density of states. The dataset was generated by Hartree–Fock mean-field calculations of candidate antiferromagnetic orders on a Wannier Hamiltonian, extracted from first-principle calculations targeting BaOsO 3 . Our machine learning model was trained using various types of spectral data, including local density of states, momentum-resolved density of states at high-symmetry points, and the lowest excitation energies from the Fermi level. Although the density of states shows good performance for machine learning, the broadening method had a significant impact on the model's performance. We improved the model's performance by designing the excitation energy as a feature for machine learning, resulting in excellent classification of antiferromagnetic order, even for test samples generated by different methods from the training samples used for machine learning. [ABSTRACT FROM AUTHOR]

Structures, electronic, and magnetic properties of transition metal (TM) inserted W6O18 clusters have been investigated by using density functional theory. The Ti@W6O18, Ni@W6O18, Zr@W6O18, Rh@W6O18, W@W6O18, and Ir@W6O18 clusters are more structurally stable while the V@W6O18, Fe@W6O18, Zn@W6O18, Y@W6O18, Nb@W6O18, Pd@W6O18, La@W6O18, Re@W6O18, Hg@W6O18 clusters are more chemically stable. The amount of charge transfer between the TM atoms and W6O18 clusters decreases with the increase of the subgroup number except for subgroup number is equal to 11 and 12. The d orbital of the 3d TM@W6O18 clusters start to make the main contributions to Fermi level except for the Cu@W6O18 and Zn@W6O18 clusters. [ABSTRACT FROM AUTHOR]

Electron transport through molybdenum chalcogenide cluster molecules Mo6Q8 (Q = S, Se, and Te) located between two 1D monoatomic aluminum chains is studied using non-equilibrium Green's function. Electron transport depends on the cluster orientation relative to electrodes, the type of chalcogen atoms, and chemical the bonding between terminal aluminum and chalcogen atoms. Distances characterized by the maximum transport properties are determined from the scan of gaps between terminal atoms of the electrode and the molecule. Conductances of Mo6Se8 and Mo6Te8 clusters are shown to be comparable at the Fermi level, and in some cases, can surpass the conductance of the Mo6S8 cluster. [ABSTRACT FROM AUTHOR]