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Two essential ingredients for the quantum anomalous Hall (QAH) effect, i.e. topological and magnetic orders, can be combined by doping magnetic ions into a topological insulator (TI) film. Through this approach, the QAH effect has been realized in chromium (Cr)- and/or vanadium (V)-doped TI (Bi,Sb)2Te3 thin films. In this work, we synthesize both V- and Cr-doped Bi2Te3 thin films with controlled dopant concentration using molecular beam epitaxy (MBE). By performing magneto-transport measurements, we find that both systems show an unusual but yet similar ferromagnetic response with respect to magnetic dopant concentration, specifically the Curie temperature does not increase monotonically but shows a local maximum at a critical dopant concentration. Our angle-resolved photoemission spectroscopy (ARPES) measurements show that the Cr/V doping introduces hole carriers into Bi2Te3, which consequently move the chemical potential toward the charge neutral point. In addition, the Cr/V doping also reduces the spin-orbit coupling of Bi2Te3 which drives it from a nontrivial TI to a trivial semiconductor. The unusual ferromagnetic response observed in Cr/V-doped Bi2Te3 thin films is attributed to the dopant-concentration-induced magnetic exchange interaction, which displays the evolution from the van Vleck-type ferromagnetism in a nontrivial magnetic TI to the Ruderman-Kittel-Kasuya-Yosida (RKKY)-type ferromagnetism in a trivial diluted magnetic semiconductor. Our work provides insights into the ferromagnetic properties of magnetically doped TI thin films and facilitates the pursuit of high-temperature QAH effect., 17 pages, 4 figures. Comments are welcome

Topological antiferromagnets have a significant role to play in the modern day electronics and spintronics due to the presence of peculiar symmetries and magnetically driven large anomalous transport behaviour. We report the observation of anomalous Hall effect in Mn3Sn polycrystalline thin films deposited on Al2O3 substrate with a large anomalous Hall conductivity of 65 (Ωcm)−1 at 3 K. The Hall and magnetic measurements show a very small hysteresis owing to a weak ferromagnetic moment present in this material. The longitudinal resistivity decreases sufficiently for the thin films as compared to the polycrystalline bulk sample used as the target for the film deposition. The anomalous Hall resistivity and conductivity decreases almost linearly with the increase in the temperature. A negative magnetoresistance is observed for all the measured temperatures with the negative decrease in the magnitude with the increase in temperature.

We consider a nanoelectromechanical system composed of a carbon nanotube suspended between two normal leads and coupled to a superconducting scanning tunneling microscope (STM) tip via vacuum tunnel barrier. Treating the nanotube as a single-level quantum dot, it is shown that an applied voltage between the superconducting STM tip and normal leads gives rise to a pumping or a cooling of the mechanical subsystem depending on the direction of the electronic flow. It is also demonstrated that the transition between these two regimes is controlled by the strength of the tunnel coupling between the nanotube and superconducting STM tip and the relative position of the electronic level. Such phenomena are realized due to a specific electromechanical coupling that is fully governed by the quantum dynamics of the Cooper pairs. The amplitude of the self-sustained oscillations in the pumping regime is analyzed numerically, and the effective temperature of the mechanical subsystem in the cooling regime is obtained.

A topological insulator (TI) interfaced with an s-wave superconductor has been predicted to host an unusual form of superconductivity known as topological superconductivity (TSC). Molecular beam epitaxy (MBE) has been the primary approach in the scalable synthesis of the TI/superconductor heterostructures. Although the growth of epitaxial TI films on s-wave superconductors has been achieved, it remains an outstanding challenge for synthesizing atomically thin TI/superconductor heterostructures, which are critical for engineering the TSC phase. Here, we used MBE to grow Bi2Se3 films with the controlled thickness on monolayer NbSe2 and performed in-situ angle-resolved photoemission spectroscopy and ex-situ magneto-transport measurements on these Bi2Se3/monolayer NbSe2 heterostructures. We found that the emergence of Rashba-type bulk quantum well bands and spin-nondegenerate surface states coincides with a marked suppression of the in-plane upper critical magnetic field of the superconductivity in Bi2Se3/monolayer NbSe2 heterostructures. This is the signature of a crossover from Ising- to Rashba-type superconducting pairings, induced by altering Bi2Se3 film thickness. Our work opens a new route for exploring a robust TSC phase in TI/Ising superconductor heterostructures., 27 pages, 4 pages, comments are welcome

Moir\'e superlattices in atomically thin van-der-Waals heterostructures hold great promise for an extended control of electronic and valleytronic lifetimes, the confinement of excitons in artificial moir\'e lattices, and the formation of novel exotic quantum phases. Such moir\'e-induced emergent phenomena are particularly strong for interlayer excitons, where the hole and the electron are localized in different layers of the heterostructure. In order to exploit the full potential of correlated moir\'e and exciton physics, a thorough understanding of the ultrafast interlayer exciton formation process and the real-space wavefunction confinement in the moir\'e potential is indispensable. However, direct experimental access to these parameters is limited since most excitonic quasiparticles are optically dark. Here we show that femtosecond photoemission momentum microscopy provides quantitative access to these key properties of the moir\'e interlayer excitons. We find that interlayer excitons are dominantly formed on the sub-50~fs timescale via interlayer tunneling at the K valleys of the Brillouin zones. In addition, we directly measure energy-momentum fingerprints of the moir\'e interlayer excitons by mapping their spectral signatures within the mini Brillouin zone that is built up by the twisted heterostructure. From these momentum-fingerprints, we gain quantitative access to the modulation of the exciton wavefunction within the moir\'e potential in real-space. Our work provides the first direct access to the interlayer moir\'e exciton formation dynamics in space and time and reveals new opportunities to study correlated moir\'e and exciton physics for the future realization of exotic quantum phases of matter., Comment: 7 pages main text, 11 pages SI

As a fundamental physical quantity of thermal phonons, temporal coherence participates in a broad range of thermal and phononic processes, while a clear methodology for the measurement of phonon coherence is still lacking. In this Lettter, we derive a theoretical model for the experimental exploration of phonon coherence based on spectroscopy, which is then validated by comparison with Brillouin light scattering data and direct molecular dynamic simulations of confined modes in nanostructures. The proposed model highlights that confined modes exhibit a pronounced wavelike behavior characterized by a higher ratio of coherence time to lifetime. The dependence of phonon coherence on system size is also demonstrated from spectroscopy data. The proposed theory allows for reassessing data of conventional spectroscopy to yield coherence times, which are essential for the understanding and the estimation of phonon characteristics and heat transport in solids in general., Comment: 4 pages, 3 figures

The discovery of infinite-layer nickelate superconductors has spurred enormous interest. While the Ni$^{1+}$ cations possess nominally the same 3$d^9$ configuration as Cu$^{2+}$ in cuprates, the electronic structure variances remain elusive. Here, we present a soft x-ray photoemission spectroscopy study on parent and doped infinite-layer Pr-nickelate thin films with a doped perovskite reference. By identifying the Ni character with resonant photoemission and comparison to density functional theory + U (on-site Coulomb repulsion energy) calculations, we estimate U ~5 eV, smaller than the charge transfer energy $\Delta$ ~8 eV, confirming the Mott-Hubbard electronic structure in contrast to charge-transfer cuprates. Near the Fermi level ($E_F$), we observe a signature of occupied rare-earth states in the parent compound, which is consistent with a self-doping picture. Our results demonstrate a correlation between the superconducting transition temperature and the oxygen 2$p$ hybridization near $E_F$ when comparing hole-doped nickelates and cuprates., Comment: 28 pages, 10 figures

Introduction of substitution atoms into carbon nanotubes is an efficient tool of controlling their physicochemical properties which allows one to expand their practical applications. Boron is one of the most promising materials used for the modification of carbon nanotubes. However until now there has been no systematization of research data on the effect of boron impurity atoms on the properties of carbon nanotubes, and this limits potential industrial applications of this nanomaterial. In this work the most efficient currently existing methods of synthesizing carbon nanotubes containing boron impurity atoms have been discussed and the physicochemical properties of the obtained nanomaterials have been analyzed. Furthermore predictions as to their potential application domains have been made on the basis of available theoretical and experimental results. Comparison of the developed technologies has shown that the most efficient synthesis method is the catalytic vapor phase deposition. The mechanical, electronic and chemical properties of boron-carbon nanotubes have also been reviewed. For a more comprehensive analysis of the dependence of the physicochemical properties of carbon nanotubes on the concentration of boron impurity a model experiment has been carried out involving quantum mechanics instruments which has shown a direct correlation between the band gap of the material and the number of boron impurity atoms. The main practical application trends of boron-containing carbon nanotubes have been outlined.

This work presents the structural and microstructural properties of zinc oxide (ZnO) powders, for that, we used X-ray diffraction (XRD), Optical microscope as characterization methods. Powder X-ray diffraction data confirm a hexagonal crystal structure formation with space group p63mc of ZnO. By Rietveld refinement, we have determined the microstructural parameters with the c axis of the preferential orientation, the ZnO replicas were clearly observed under an optical microscope. Band structure and density of states of the phase of crystal ZnO computed using Ab Initio methods, confirmed that pure ZnO is a direct band gap semiconductor in hexagonal wurtzite structure.

SrTiO$_3$, a quantum paralectric, displays a detectable phonon thermal Hall effect (THE). Here we show that the amplitude of THE is extremely sensitive to stoichiometry. It drastically decreases upon substitution of a tiny fraction of Sr atoms with Ca, which stabilizes the ferroelectric order. It drastically increases by an even lower density of oxygen vacancies, which turn the system to a dilute metal. The enhancement in the metallic state exceeds by far the sum of the electronic and the phononic contributions. We explain this observation as an outcome of three features: i) heat is mostly transported by phonons; ii) the electronic Hall angle is extremely large; and iii) there is substantial momentum exchange between electrons and phonons. Starting from Herring's picture of phonon drag, we arrive to a quantitative account of the enhanced THE. Thus, phonon drag, hitherto detected as an amplifier of thermoelectric coefficients, can generate a purely thermal transverse response in a dilute metal with a large Hall angle. Our results reveal a hitherto unknown consequence of momentum-conserving collisions between electrons and phonons.ely thermal transverse response in a dilute metal with a large Hall angle. Our results reveal a hitherto unknown consequence of momentum-conserving collisions between electrons and phonons., Comment: 9 pages, six figures and a supplement

Semiconducting clathrates are attracting a great deal of attention as potential candidates of thermoelectric material based on a design concept called Phonon Glass and Electron Crystal (PGEC). Since most of the thermoelectric clathrates are n-type, developing a p-type clathrate with high thermoelectric performance is an important issue. In this study, the electronic structure and thermoelectric properties of Ba8Cu6Ge40 clathrate are calculated based on density functional theory (DFT) to search for new p-type clathrates. An energy gap is formed in the electronic band structure of Ba8Cu6Ge40, and the Fermi energy lies in the valence band, indicating that Ba8Cu6Geぃis a p-type semiconductor. The effective mass of the valence band is larger than that of the conduction band. The Seebeck coefficient for p-type is larger than that for n-type, reflecting the difference in effective mass. According to the dependence of Seebeck coefficient and electrical conductivity on the chemical potential, adjusting the Fermi energy, corresponding to the carrier concentration, to the optimum value improves the power factor. Therefore, the results of DFT calculation show that Ba8Cu6Ge40 has excellent properties as a candidate for p-type thermoelectric materials.

Quartz samples taken from the ore veins of the Darasun gold deposit (Eastern Transbaikalia, Russia) were studied using electron paramagnetic resonance (EPR) and laser ablation (LA) methods. The purpose of the research was to clarify the behavior of the Al impurity during quartz crystallization and its subsequent recrystallization. The results of the research were used to determine the genetic informativeness of the Al impurities concentration in ore quartz. A separate study of the regularities of the distribution of Al impurity in the regions of crystalline structure and in the zones of crystal lattice distortions was carried out. In the regions of crystalline structure, the Al impurity concentration NAL was determined by the concentration of paramagnetic Al–O–-centers associated with the presence of substitutional Al3+ ions. The content of the Al impurity in the zones of crystal lattice distortions was judged by the difference between the gross concentrations of aluminum CAl and the values of NAL. It was taken into account that the intensity and direction of the studied processes can be influenced by the temperature of quartz formation and the degree of its recrystallization. The temperature of quartz formation was estimated by the values of Ti impurity concentration, and the degree of recrystallization was estimated by the content of Li impurity CLi in the mineral. It was found that the amount of Al impurity localized in the zones of crystal lattice distortions is an order of magnitude higher than that present in the zones of crystalline structure. It is shown that this phenomenon is explained by the high ability of the zones of crystal lattice distortions to capture of Al impurity during quartz crystallization. The amount of Al impurity trapped by quartz increases sharply with an increase in the temperature of the mineral formation. In areas of regions of crystalline structure, a different picture is observed − impurity capture during crystallization proceeds with low intensity and is not so critically dependent on temperature. It was found that the Al impurity in the considered zones behaves differently during quartz recrystallization. If Al impurity capture continues in the regions of crystalline structure, then Al impurity removal from quartz can occur in the zones of crystal lattice distortions at high CAl values. Based on the data obtained, the areas of use of aluminum impurity contents as a typomorphic feature of ore quartz were determined. The Al impurity concentrations proved to be suitable for use in cases of low ore formation temperatures, and its gross CAl contents have the prospect of wider use. It is noted that a characteristic feature for quartz from high productivity zones is a negative angle of slope of the CAl(CLi) dependence plot.

In the first paper of this series, a new formula for central film thickness of slender contacts has been proposed. In this paper, interferometry measurement of the film thickness in slender elliptic contacts is performed for comparison with film thickness distribution of EHL simulation. The new film thickness formula presented in part I of this paper series is successfully validated by comparison with the experimental data. State-of-the-art minimum film thickness formulas are compared with the experimental results and results obtained through a multilevel EHL solver. Significant deviation of the analytical minimum film thickness formulas regarding both numerical and experimental results is given. Therefore, an alternative approach for calculation of minimum film thickness via the film thickness ratio with central film thickness is proposed, which yields promising results for moderately slender elliptic EHL contacts.

We report on the influence of Al doping on the structural, morphological and vibrational properties of hematite crystallite synthesized by using the hydrothermal method. The structural property of the pristine and Al doped hematite samples are extensively characterized by the Rietveld profile refinement of X-ray diffraction data. The structural refinement suggests that both the pristine and the doped compounds are stabilized in the hexagonal R 3 c symmetry. Doping with Al induces a compressive strain in the hematite lattice, which is further reflected in the spectroscopic Raman studies. It is also observed that the Al atom has a significant influence on the growth mechanism of hematite crystallites. Temperature dependent Raman study performed in the Al doped hematite sample brings out anomalous behaviour of phonon modes and line widths around the temperature region of 150 K. These anomalies observed around the temperature region of 150 K are suggestive of the presence of spin-phonon coupling associated with the Morin transition in the Al doped hematite. Our detailed structural and Raman spectroscopic analyses suggest that the Al doped hematite can be a potential magnetodielectric candidate.

The phonon transport is intensively related to microstructure defects. Herein, a unique high-pressure sintering technology (GPa-level) was applied to modify the microstructure of pristine SnTe. There are many nano-domains exist in the high pressured NaCl-type SnTe binary compounds. The fast Fourier transform images show the domain phases have two sets of reflections with comparable intensity and exhibit doublet periodicities of special lattice planes, which demonstrates the domain phases are the CuPt and CuAu-I-type variants evolved from the NaCl-type matrix phase. An in-depth investigation indicates the constructions of the domain phase are related to locally off-stoichiometric of SnTe and the introduced strong inner-stress during high pressure sintering process. Additionally, a calculation of the phonon transport discloses the nano-domains restrict the phonon relaxation time by orders of magnitude over a wide phonon frequency range. As a result, a wide frequency phonon scattering network can be established to lower the lattice thermal conductivity.

Epitaxial Ni–Mn–Ga thin films have promising application potential in micro-electro-mechanical sensing and actuation systems. To date, large abrupt magnetization changes have been observed in some epitaxial Ni–Mn–Ga thin films, but their origin - either from magnetically induced martensite variant reorientation (MIR) or magnetic domain evolution - has been discussed controversially. In the present work, we investigated the evolutions of the magnetic domain and microstructure of a typical epitaxial Ni–Mn–Ga thin film through wide-field magneto-optical Kerr-microscopy. It is demonstrated that the abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the MIR.

In order to analyze the influence of Al-Ag doping on the electrical properties of eigenstate and oxygen vacancy ZnO resistor valves, first principles were used to analyze the crystal structure of Al-Ag single doping and co-doping eigenstate and oxygen vacancy ZnO. Energy, band structure, density of states and electrical conductivity have been calculated. The results show that after doping with acceptor elements, the lattice parameters of the eigenstate unit cell and the oxygen vacancy unit cell are increased, and their potential can be increased. Gradient; when Ag is doped, its formation energy is the lowest, indicating that Ag doping is easier and higher stability; when oxygen vacancies, the nonlinear characteristic of ZnO resistor valve is better than that of eigenstate, but whether it is single doping or Co-doping does not improve its nonlinear characteristics better; doping will slightly increase its conductivity, and the conductivity of Ag doping is the best.

Doping enables manipulation of both the electrical and optical properties of halide perovskites. Herein, we incorporated Te4+ into Cs2ZrCl6 single crystal, simultaneously preserving the vacancy-ordered structure, to obtain an efficient yellow-emitting perovskite with a near-unity photoluminescence quantum yield (PLQY ≈ 97.6%). Te4+ doping modifies the hue and emission color of pristine Cs2ZrCl6, generates new absorption channels, and successfully extends the excitation energy from

The Fe and Co single and co-doping effects on the structural and magnetic properties of NiO nanoparticles (NPs) have been studied. The Fe and Co doping into NiO system did not induce any other possible secondary phase (other than NiO) and the average crystallite size was found to be in a narrow range of 33–40 nm which is suitable for studying the doping effects. Room temperature ferromagnetic resonance (FMR) measurements demonstrated the existence of a net magnetization in antiferromagnetic (AFM) NiO NPs which was observed to be increased with an increasing Fe doping and decreasing Co doping concentration. The scattered differential FMR signal for 8% Co doped NiO NPs revealed the presence of randomly oriented magnetic moments in the core of the NPs. However, decreasing the Co doping concentration and increasing the Fe doping concentration increased the degree of homogeneity of the spin structure in the system. The M − H loops taken at room temperature with S-like shape confirmed the presence of a weak ferromagnetism in the Fe doped samples in accordance with FMR analysis and attributed to the double exchange mechanism in these NPs. In ZFC/FC curves, a small peak at low temperatures, in the range of 9–18 K for all the samples, indicates the magnetization contribution from the uncompensated surface spins of these NPs. In addition, a relatively broad peak for higher Fe doping concentrations at higher temperatures indicates the onset of magnetization from the core of these NPs, where Fe and Ni ions may couple parallel or anti-parallel to each other. In summary, Co–Fe co-doping induced a core magnetization in AFM NiO NPs system and makes it attractive for various magnetic applications.

All available thermodynamic data and phase diagram data in the Al2O3–ZrO2, CaO–Al2O3–ZrO2, and Al2O3–SiO2–ZrO2 systems at 1 bar total pressure were critically evaluated and assessed simultaneously to obtain a set of the optimized Gibbs energies of all phases in the systems. Due to the lack of reliable data on the mutual solubility of Al2O3 and ZrO2, key phase diagram experiments in the Al2O3–ZrO2 binary system were carried out by using a classical phase equilibrium and quenching technique followed by the EPMA phase analysis. Based on the optimized Gibbs energies, the reliable experimental phase diagram and thermodynamic property data of the Al2O3–ZrO2, CaO–Al2O3–ZrO2, and Al2O3–SiO2–ZrO2 systems are well reproduced, and unknown phase diagram and thermodynamic properties are predicted.

By absorbing and transferring the photons (nearby bandgap) to photoelectrons, non–compensated (Ce4+ dopants) doping Bi5Ti3FeO15 ferroelectric films present switchable and stable photovoltaics. The defect dipole attraction in non–compensated doping films not only narrows the bandgap effectively by the creation of tunable intermediate sub–band (gap state), but enhances separation of electron–hole pairs in the visible–light region. The concept is proved by dramatic redshift of optical absorbance and intense photovoltaics. Subsequently, contrast investigations of equivalent–compensated doping films offer solid experimental evidences. Furthermore, the intensity of Coulomb attraction between defect dipoles can be destroyed by thermal perturbation, which is empirically supported by the abrupt drop of temperature dependent photovoltage at 340 K. These results demonstrate that non–compensated doping can be a promising route to construct more efficient energy transfer devices.

The nature of the change in the Fermi level of silicon under the influence of dopants, point defects, and dislocations has been determined. The parameters of the diffusion of impurities, the conditions for their appearance and removal in the process of directional crystallization and the post-crystallization period have been established. The expediency of doping silicon with boron and phosphorus was shown, and large single crystals were obtained. The mechanisms of elimination of structural defects have been clarified. The mobility and lifetime of charge carriers in perfect silicon single crystals under radiation exposure have been determined. The expediency of using p-type silicon as a base material for solar modules for space purposes is shown.

We investigate temperature, pressure, and localization dependence of thermoelectric properties, phonon and de Haas–van Alphen (dHvA) frequencies of the anti-ferromagnetic (AFM) CeIn $$_3$$ 3 using density functional theory (DFT) and local, hybrid, and band correlated functionals. It is found that the maximum values of thermopower, power factor, and electronic figure of merit of this compound occur at low (high) temperatures provided that the 4f-Ce electrons are (not) localized enough. The maximum values of the thermopower, power factor, electronic figure of merit (conductivity parameters), and their related doping levels (do not) considerably depend on the localization degree and pressure. The effects of pressure on these parameters substantially depend on the degree of localization. The phonon frequencies are calculated to be real which shows that the crystal is dynamically stable. From the phonon band structure, the thermal conductivity is predicted to be homogeneous. This prediction is found consistent with the thermal conductivity components calculated along three Cartesian directions. In analogous to the thermoelectric properties, it is found that the dHvA frequencies also depend on both pressure and localization degree. To ensure that the phase transition at Néel temperature cannot remarkably affect the results, we verify the density of states (DOS) of the compound at the paramagnetic phase constructing a non-collinear magnetic structure where the angles of the spins are determined so that the resultant magnetic moment vanishes. The non-collinear results reveal that the DOS and whence the thermoelectric properties of the compound are not changed considerably by the phase transition. To validate the accuracy of the results, the total and partial DOSs are recalculated using DFT plus dynamical mean-field theory (DFT+DMFT). The DFT+DMFT DOSs, in agreement with the hybrid DOSs, predict the Kondo effect in this compound.

We present a detailed study on band structure-dependent properties such as electrical conductivity, the charge of carriers and Seebeck coefficients of graphene nano-ribbons (GNRs) doped with the magnetic impurities Fe and Co since the spin thermopower could be considerably enhanced by impurities. Thermoelectric properties of two-dimensional systems are currently of great interest due to the possibility of heat to electrical energy conversion at the nanoscale. The thermoelectric properties are investigated using the semi-classical Boltzmann method. The electronic band structure of doped nano-ribbons is evaluated by means of density-functional theory in which the Hubbard interaction is considered. Different types of nano-ribbons (armchair-edge and zigzag-edge) and their thermoelectric features such as conductivity and Seebeck coefficient in the presence and absence of magnetic impurities have been studied.

Doping of isovalent (S, Se, and Te) elements in ZnO is a new doping method. However, the factors affecting the photocatalytic performance of a doped system by triaxial strain are often ignored. In this study, we have applied strain on model and performed first-principle calculation to investigate the effect of triaxial strain on the stability of the doped system, red shift of the absorption spectrum, electric dipole moment, and carrier lifetime. Calculation results showed that all doped systems exhibited high binding energy and stability under unstrained conditions. However, when the applied strain was increased, the energy of all the systems increased, and the stability decreased. The stability, red shift of absorption spectrum, electric dipole moment, and carrier lifetime of all doped systems were studied. When the tensile strain was 5%, the red shift of the absorption spectrum and the electric dipole moment of the doped system (Zn36SO35) were the largest. Moreover, the carrier lifetime of the doped system (Zn36SO35) was the longest. Considering the red shift of the absorption spectrum, electric dipole moment, and carrier lifetime, the photocatalytic performance of the doped system (Zn36SO35) was the best, when the tensile strain was 5%.

Molecular doping is a key process to increase the density of charge carriers in organic semiconductors. Doping induced charges in polymer semiconductors result in the formation of polarons and or bipolarons due to the strong electron vibron coupling in conjugated organic materials. Identifying the nature of charge carriers in doped polymers is essential to optimize the doping process for applications. In this work, we use Raman spectroscopy to investigate the formation of charge carriers in molecularly doped poly 3 hexylthiophene 2,5 diyl P3HT for increasing dopant concentration, with the organic salt dimesityl borinium tetrakis penta fluorophenyl borate Mes2B [B C6F5 4] amp; 8722; and the Lewis acid tris pentafluorophenyl borane [B C6F5 3]. While the Raman signatures of neutral P3HT and singly charged P3HT segments polarons are known, the Raman spectra of doubly charged P3HT segments bipolarons are not yet sufficiently understood. Combining Raman spectroscopy measurements on doped P3HT thin films with first principles calculations on oligomer models, we explain the evolution of the Raman spectra from neutral P3HT to increasingly doped P3HT featuring polarons and eventually bipolarons at high doping levels. We identify and explain the origin of the spectral features related to bipolarons by tracing the Raman signature of the symmetric collective vibrations along the polymer backbone, which compared to neutral P3HT redshifts for polarons and blueshifts for bipolarons. This is explained by a planarization of the singly charged P3HT segments with polarons and rather high order in thin films, while the doubly charged segments with bipolarons are located in comparably disordered regions of the P3HT film due to the high dopant concentration. Furthermore, we identify additional Raman peaks associated with vibrations in the quinoid doubly charged segments of the polymer. Our results offer the opportunity for readily identifying the nature of charge carriers in molecularly doped P3HT while taking advantage of the simplicity, versatility, and non destructive nature of Raman spectroscopy

Strain-induced magnetic anisotropy reversal and 100% spin polarization are realized in the MCGS/MgO system, which can be used in magnetic tunnel junctions where the high/low resistance is rotated solely by the voltage-generated strain.

We have studied here the impact of Al and Ce co-doping in ZnO nanoparticles obtained by sol-gel co-precipitation. Fourier Transform Infrared (FTIR) spectroscopy revealed the presence of Zn O bond in un-doped sample and Al O and Ce O bonds were seen in doped and co-doped samples. UV–Vis spectra depicted an absorption dip in UV region and the band gap was seen to decrease on doping and co-doping. The red-shift of the band gap is attributed to the creation of deeper states by doping and co-doping. Photoluminescence (PL) spectra had two major emission peaks at 402 and 428 nm, whose intensities were enhanced by doping and co-doping. Scanning electron microscopy studies indicated spherical morphology of nanoparticles (NPs) in un-doped ZnO, which were transformed to granules and pin-like structures on doping with Al, which became sharper at the edges on subsequent co-doping with Ce.

Silicene nanoribbons have been studied a lot in recent years, it is a nanostructure with enormous applications. The doping of another element into the unit cell changes the electrical and magnetic properties of the material, which creates new research directions in materials science. Based on the DFT theory, this work studies the doping phosphorus atoms and in silicene nanoribbons in the presence of an external electric field of about 0.1 V/Angstrom. The work also limited the doping study in two cases: The doping case of one phosphorus atom and the 100% doping configuration. There are two doping positions of a phosphorus atom, the top position, and the valley position, and the formation energy will find the optimal position. The energy band structure and state density will also be drawn, examined, and compared.

We investigated the effect of the thickness of superconducting layer on the competition between ferromagnetism and superconductivity. The epitaxial bilayer systems consisting of GdBa2Cu3O7-x (GdBCO) with varying thickness and La0.7Sr0.3MnO3 (LSMO) were grown on (001) SrTiO3 (STO) substrate. From the spectroscopic measurements, we observed an existence of a possible structural coupling between the GdBCO and the LSMO layers. The structural coupling is found to depend on the GdBCO thickness and to induce different types of strain on both layers, leading to the competition between the ferromagnetic and the superconducting orders. With respect to the flux pinning, an additional pinning contribution besides magnetic pinning induced by LSMO is emerged by the structural coupling, which is attributed to local atomic disorder. Controlling the thickness of GdBCO modifies the structural coupling and consequently, the degree of additional pinning contribution aroused by disorder on the CuO2 plane can be adjusted. An appropriate structure with a certain thickness amplifies the hybrid effect of magnetic pinning and additional pinning, resulting in an enhancement of the critical current density at high magnetic fields. Our findings suggest a possibility of controlling complex flux pinning through an optimization of structural coupling between the GdBCO and the LSMO layers.

Superconducting nanowire fiber mats of Bi2Sr2CaCu2O8, YBa2Cu3O7 and GdBa2Cu3O7 were fabricated using electrospinning and solution blow-spinning. Fiber mats consisting of individual nanowires with long lengths (∼100 µm) and diameters between 150 and 500 nm were obtained. Magnetic properties of the samples were measured by SQUID magnetometry. Having studied a large number of such samples, we find that only the YBCO fiber mats exhibit the paramagnetic Meissner effect (PME), whereas the other materials do not. To explain these observations, we regard the current flow through the nanowires, the distinctly different current densities and the vortex dimensionality at temperatures close to Tc.

Phonon transfer in irregular shapes is important for assessing the influence of shape effect on thermal transport characteristics of low-scale films. It becomes critical for evaluating the contribution of the scattering phonons to the phonon intensity distribution inside the film. Hence, the sub-continuum ballistic-diffusive model is incorporated to formulate the phonon transport in an irregular geometry of low-size film adopting the transient, frequency-independent, equation of phonon radiative transfer. The discrete ordinate method is used in the numerical discretization of the governing transport equation. It is demonstrated that the geometric feature of the film influences the phonon intensity distribution within the film material. The transport characteristics obtained from the Fourier and the ballistic-diffusive models are markedly different in their spatial and temporal behavior. This is true when the device sizes are of the same order of magnitude as the mean-free path of the heat carriers.

In metal-N-C systems, doped metals have an obvious valence change in the process of Li-ion deintercalation, which is in agreement with the operational principle of traditional anode materials. Doped metals will transfer some electrons to the neighboring N atoms to improve the valence state. Along with Li adsorption, the charge transferred to the nearest N or C from Li is less compared to that transferred to the doped metal. Hence, doped metals have an obvious valence change in the process of Li-ion deintercalation, and doped N just serves as a container for holding electrons. The local states of C and N p electrons in the Co-N-C structure can be fully destroyed, which can effectively improve the electronic properties of graphene.

The anharmonicity of the Ruddlesden Popper metal-halide lattice, and its consequences on their electronic and optical properties, is paramount in their basic semiconductor physics. It is thus critical to identify specific anharmonic optical phonons that govern their photophysics . Here, we address the nature of phonon-phono scattering probabilities of the resonantly excited optical phonons that dress the electronic transitions in these materials by means of variable-temperature resonant impulsive stimulated Raman measurements. Based on the temperature dependence of the coherent phonon lifetimes, we isolate the dominant anharmonic phonon and quantify its phonon-phonon interaction strength. Intriguingly, we also observe that the anharmonicity is distinct for different phonons, with a few select modes exhibiting temperature-independent coherence lifetimes, indicating their predominantly harmonic nature. However, the population and dephasing dynamics of excitons are dominated by the anharmonic phonon.

The spatial confinement of atoms at surfaces and interfaces significantly alters the lattice dynamics of thin films, heterostructures and multilayers. Ultrathin films with high dielectric constants (high-k) are of paramount interest for applications as gate layers in current and future integrated circuits. Here we report a lattice dynamics study of high-k Eu2O3 films with thicknesses of 21.3, 2.2, 1.3, and 0.8 nm deposited on YSZ(001). The Eu-partial phonon density of states (PDOS), obtained from nuclear inelastic scattering, exhibits broadening of the phonon peaks accompanied by up to a four-fold enhancement of the number of low-energy states compared to the ab initio calculated PDOS of a perfect Eu2O3 crystal. Our analysis demonstrates that while the former effect reflects the reduced phonon lifetimes observed in thin films due to scattering from lattice defects, the latter phenomenon arises from an ultrathin EuO layer formed between the thin Eu2O3 film and the YSZ(001) substrate. Thus, our work uncovers another potential source of vibrational anomalies in thin films and multilayers, which has to be cautiously considered

Two-dimensional (2D) Sn-based perovskites are a kind of non-toxic environment-friendly luminescent material. However, the research on the luminescence mechanism of this type of perovskite is still very controversial, which greatly limits the further improvement and application of the luminescence performance. At present, the focus of controversy is defects and phonon scattering rates. In this work, we combine the organic cation control engineering with temperature-dependent transient absorption spectroscopy to systematically study the interband exciton relaxation pathways in layered A2SnI4 (A = PEA+, BA+, HA+, and OA+) structures. It is revealed that exciton-phonon scattering and exciton-defect scattering have different effects on exciton relaxation. Our study further confirms that the deformation potential scattering by charged defects, not by the non-polar optical phonons, dominates the excitons interband relaxation, which is largely different from the Pb-based perovskites. These results enhance the understanding of the origin of the non-radiative pathway in Sn-based perovskite materials., Exciton scattering in perovskite is an important phenomenon dictating the optoelectronic performance. Here, the authors confirm the deformation potential scattering by charged defects, not by the non-polar optical phonons, dominates the excitons interband relaxation in 2D Sn-based perovskites.

The dynamics of exciton–exciton annihilation in WS2 homostructures can be flexibly controlled by changing the interlayer twist angle. Exciton-exciton annihilation is strongly suppressed at a small interlayer twist angle.

This research article presents the preliminary findings of an investigation into the manufacturing and characterization of a Ti alloy powder utilizing a high-energetic ball milling process. To mechanically alloy elemental powders, a high-energetic Ball Mill used. Mechanically alloyed powders analysed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission electron microscope to investigate structural, parameters. As indicated by XRay Diffraction data indicating crystallite size reduces to the nano scale regime, the elemental powders simultaneously alloyed with increasing ball milling duration. However, partial amorphization of elemental powders found during extended milling times. The results of transmission electron microscope (TEM) indicate a halo picture as well as crystalline rings, and also a shift from crystalline to partly amorphous structure during the ball milling process.

One of the most effective option of photocatalysts for water splitting is doped strontium titanate, SrTiO3. It has a high rate of photo-generated charge transfer and limited photocatalytic activity for water splitting. The search of an appropriate photocatalyst having a high visible light absorption as well as fast charge transportation is extremely needed, however it is a difficult task. The structural, electronic and optical properties of sulfur-doped SrTiO3 and nitrogen-doped SrTiO3 are investigated using calculations based on density functional theory (DFT). According to the band structure calculations, the O-2p states represented the higher levels of the valence band of pure SrTiO3. When S and N atoms are introduced into the SrTiO3 structure on the O site, electronic structure findings indicate that doping the Sulfur (S) atoms reduced the band gap significantly, whereas doping of N atoms increased the bandgap of SrTiO3. According to our results, the N-doped SrTiO3 has a sufficient band gap of 2.03 eV, as well as suitable high visible light absorption and charge carrier transportation. The optical properties showed that N-doped SrTiO3 has good photosensitivity for visible light. In addition, we have found a significant impurity state that differs from O 2p-states, which can increase photocatalytic efficiency. The results of studies of electronic band structure showed that electron-hole transportation was well consistent with the experimental data. Thus, the N-doped SrTiO3 in this study is indeed an attractive candidate for hydrogen evolution throughout the visible light range, providing a logical base for the establishment of innovative photocatalysts.

Radial superlattices are nanostructured materials obtained by rolling-up thin solid films into spiral-like tubular structures. The formation of these "high-order" superlattices from two-dimensional crystals or ultrathin films is expected to result in a transition of transport characteristics from two-dimensional to one-dimensional. Here, we show that a transport hallmark of radial superlattices is the appearance of magnetoconductance modulations in the presence of externally applied axial magnetic fields. This phenomenon critically relies on electronic interlayer tunneling processes that activates an unconventional Aharonov-Bohm-like effect. Using a combination of density functional theory calculations and low-energy continuum models, we determine the electronic states of a paradigmatic single-material radial superlattice -- a two-winding carbon nanoscroll -- and indeed show momentum-dependent oscillations of the magnetic states in axial configuration, which we demonstrate to be entirely due to hopping between the two windings of the spiral-shaped scroll., Comment: 21 pages, 4 figures. To appear in Nanoscale Horizons

In this report, nonlinear optical single crystals of L Isoleucine D Alanine a potential nonlinear optical material was conveniently grown by slow solvent evaporation technique. The grown crystals were characterized by single crystal X-ray diffractometry (XRD), optical absorption spectrum to reveal the cut off wavelength and the optical band gap energy. The structure is obtained using Gaussian 09 software. The micro hardness test of the sample revealed the category which the crystal belongs to. The SHG efficiency of the grown material is determined using NLO test using Kurtz Perry powder technique.

We study the surface crystalline and electronic structures of the antiferromagnetic topological insulator MnBi2Te4 using scanning tunneling microscopy/spectroscopy (STM/S), micro(μ)-laser angle-resolved photoemission spectroscopy (ARPES), and density functional theory calculations. Our STM images reveal native point defects at the surface that we identify as BiTe antisites and MnBi substitutions. Bulk X-ray diffraction further evidences the presence of the Mn-Bi intermixing. Overall, our characterizations suggest that the defects concentration is nonuniform within crystals and differs from sample to sample. Consistently, the ARPES and STS experiments reveal that the Dirac point gap of the topological surface state is different for different samples and sample cleavages, respectively. Our calculations show that the antiparallel alignment of the MnBi moments with respect to those of the Mn layer can indeed cause a strong reduction of the Dirac point gap size. The present study provides important insights into a highly debated issue of the MnBi2Te4 Dirac point gap., We acknowledge support by the Spanish Ministerio de Ciencia e Innovacion (Grant no. PID2019-103910GB-I00, PGC2018–093291–B–I00, PGC2018-097028–A–I00, and PGC2018-098613–B–C21) and Saint Petersburg State University (project ID No. 73028629). IMDEA Nanociencia acknowledges support from the “Severo Ochoa” Program for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). M.G. has received financial support through the Postdoctoral Junior Leader Fellowship Program from “la Caixa” Banking Foundation. Z.S.A. and N.T.M. acknowledge the support of the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EIF-BGM-4-RFTF-1/2017-21/04/1-M-02). I.I.K., D.E., and A.M.S. acknowledge the support from the Russian Science Foundation (Grant No. 18-12-00062) and the Russian Foundation of Basic Researches (Grant No. 20-32-70179).

A Metropolis Monte Carlo simulation is used in this paper to investigate the temperature dependency of the hysteresis loops of a spin-1 bilayer with square monolayers. In this system, the atoms interact ferromagnetically in-plane, with either ferromagnetic or antiferromagnetic interplane interactions. The effects of four distinct combinations of the Hamiltonian parameters on the hysteresis behaviours are discussed in detail. The geometry of the hysteresis loops changes depending on how the exchange couplings are combined. With ferromagnetic interlayer coupling, only the central hysteresis loop opens while for the antiferromagnetic case, the hysteresis loop becomes a double loop for the specific combination of coupling strengths. Additionally, in all these cases, the area of the hysteresis loops grows with the gradual lowering of the temperature., 8 pages, 5 coloured figures. Comments are welcome via e-mail

International audience; Foam film elasticity plays a significant role in film drainage and film stability and is thus expected to influence foam dynamical properties. It strongly depends on the foaming solution composition and differs from the interface elasticity measured in unconfined geometries. We use a deformable frame to deform an assembly of five films and we measure the tension and extension of each film. This provides a simple and accurate determination of the film elasticity, in the linear and non-linear regimes, for a set of SDS/dodecanol mixtures, at various concentrations. We show that the non-linear elastic behavior is well reproduced by Mysel's model coupled with a Langmuir coadsorption isotherm for a large range of chemical compositions.

Density functional theory calculations to investigate the effect of single and double germanium atom doping on the geometric structure and electronic properties of boron clusters with 10 to 20 atoms.

In this work, sol–gel spin coating route was utilized for the synthesis of undoped, Co-doped, Al-doped, and Ni-doped thin films of ZnO. XRD results show that deposited thin films possess a hexagonal lattice with preferential c-axis orientation. A reduction in lattice constants was observed owing to the substitution of Zn2+ ions by lower radius doping ions Co2+, Al3+, and Ni2+. The effect of doping is to reduce the crystallite size. Raman spectra show a characteristic peak of hexagonal ZnO at 439 cm−1. PL spectrum of all films demonstrates a UV emission ascribed to near band edge transition and a green emission band. All thin films with the transmission in visible regions above 86% are highly transparent. The doping element influenced the band gap of doped thin films.

In this work, we performed molecular dynamics (MD) simulations on the interactions between a basal edge dislocation and point defects including vacancies and self-interstitial atoms in magnesium. Simulation results suggest that both self-interstitial atoms and vacancies have a blocking effect on dislocation motion, but the blocking effect of vacancies is much weaker than that of self-interstitial atoms. During interactions, self-interstitial atoms are absorbed and move with dislocation, and the edge dislocation climbs after absorbing self-interstitial atoms. In contrast, vacancies cannot be absorbed. To explain these observations, the binding energy and migration energy are calculated. The binding energy of both vacancies and self-interstitial atoms increases as they approach the dislocation core, seemingly indicating that they can be absorbed. However, the migration barrier of a vacancy is found to be about two orders in magnitude higher than that of a self-interstitial atom. Therefore, only self-interstitial atoms are absorbed, while vacancies cannot.

Pure and 1 mol% thiourea doped potassium hydrogen phthalate single crystals were grown by slow evaporation method. Single crystal XRD confirms the crystalline perfection of the crystal. FTIR studies confirm the presence of functional group. UV–Vis studies reveal the good optical transparency of the crystal. The thermal stability of the crystal was confirmed by thermal studies. The strength of the crystal was determined by Vickers micro hardness studies. The dielectric constant and dielectric loss at various temperatures was determined. The nonlinear optical efficiency of 1 mol% thiourea doped KHP and pure KHP crystal was identified by SHG studies.

Trioxides of rubidium, strontium, and ruthenium belong to the family of alkali and alkaline earth ruthenates. SrRuO3 crystallizes in various symmetry classes—orthorhombic, tetragonal, or cubic—whereas RbRuO3 is perovskite (cubic) structured and crystallizes only in the cubic space group Pm3¯¯¯m(No. 221). In this study, we investigated the structural stability as well as the electronic and magnetic properties of two cubic perovskites SrRuO3 and RbRuO3. We established the corresponding lattice parameters, magnetic moments, density of states (DOS), and band structures using ab‑initio density‑functional theory (DFT). Both compounds exhibited a metallic ferromagnetic ground state with lattice parameter values between 3.83 and 3.96 Å; RbRuO3 had magnetic moments between 0.29 and 0.34 µBwhereas SrRuO3 had magnetic moments between 1.33 and 1.66 µB. This study paves way for further RbRuO3 research.

Electron transport processes in oxide superconducting heterostructures with epitaxially grown magnetic thin-film interlayers, in which the interaction of superconducting correlations and magnetic ordering occurs due to superconducting and magnetic proximity effects, have been studied experimentally. Hybrid mesa-heterostructures were prepared from thin-film bottom cuprate superconductor (S), magnetic (M) interlayer made of manganite or an antiferromagnetic cuprate, and the upper electrode made from an ordinary superconductor. When the cuprate antiferromagnetic material was replaced by a ferromagnetic manganite interlayer, the superconducting current was suppressed, although the thin magnetic film was several times thinner, 5 nm, and the temperature was lowered to 0.3 K. At low temperatures dependences of differential resistance vs. voltage for mesa-heterostructures with manganite interlayer featured mini-gap low-energy states.