Journal of Physics: Condensed Matter最新文献

We investigate theIVcurve and magnetic moment amplitude in a coupled system consisting of a single-domain nanomagnet and Josephson junction (JJ) driven by external electromagnetic radiation. The role of the magnetic field generated by the quasiparticle current on the locking of magnetic moment precession and Josephson oscillations is demonstrated. It leads to the appearance of a bubble-like structure in the bias current dependence of the maximal amplitude of magnetic moment. This bubble feature corresponds to the locking of magnetic precession by external radiation, analogous to the well-known Shapiro steps in theIVcurve of JJs. The locking properties in the system can be controlled through parameters of the external signal, such as frequency and amplitude. These findings enable the control of magnetic precession through external radiation in Josephson hybrid structures, which can be useful for applications in superconducting spintronics.

Synchrotron x-ray spectroscopy was employed to determine the effects of nanostructuring on electronic band structure in V₂O₅, a promising cathode material and widely used catalyst. V₂O₅nanoparticle and bulk powders were characterized via P-XRD, electron microscopy, and diffuse reflectance ultraviolet/visible/near-infrared spectroscopy to confirm the optical bandgap. X-ray emission spectroscopy revealed the nanoparticle valence band O 2pstates to be upshifted relative to the bulk, while x-ray absorption spectroscopy and resonant inelastic x-ray scattering showed the lowest V 3dconduction band states to be static. Together, these changes (in conjunction with an increased density of unoccupied lower conduction band states) produce a shrunken bandgap in the V₂O₅nanoparticles that defies the Burstein-Moss effect. Changes in nanoparticle band structure are generally attributed to oxygen vacancy defects. While nanostructure bandgap reduction is in line with much previous computational work, it is unexpected from most previous experimental results. To our knowledge, this is the first synchrotron x-ray spectroscopy study of a shrunken bandgap achieved in pure V₂O₅nanoparticles.

Single crystals of disordered Mn_4-xCr_xAl₁₁have been synthesized via the flux method. EDS on several crystals of various sizes and shapes revealed an average molar ratio of 17:9:74 for Mn:Cr:Al, while x-ray diffraction on three different crystals yield compositions Mn_2.26Cr_1.74Al₁₁(Mn_4-xCr_xAl₁₁,x= 1.74), Mn_0.83Cr_3.17Al₁₁, and Mn_1.07Cr_2.93Al₁₁. This compound crystallizes in space groupP1¯, isostructural with both Mn₄Al₁₁and Cr₄Al₁₁. Magnetic measurements on several crystals show that this disordered compound is ferrimagnetic with a low effective moment ofμeff≈1.012±0.004μB/f.u.and a non-reachable transition temperature. Density functional theory calculations display opening of a bandgap in the spin-up channel near the Fermi level with increasing Cr content, an indication of half-metallicity.

Constructing heterostructures has been used as an effective way to circumvent the shortcomings of composite layers since the interactions and charge transfer between individual layers can thus change the properties in forming heterostructure. In this work, the stability and physical properties of two-dimensional van der Waals CrI₃/Nb₃Cl₈heterojunction in different stacking modes have been investigated using the first principles calculations based on density functional theory. The results demonstrate that the most stable CrI₃/Nb₃Cl₈heterojunction possesses a typical type-II band alignment with a 0.753 eV indirect band gap. The electrons moves from the Nb₃Cl₈layer to the CrI₃layer due to the former one has a higher energy level for valence band maximum, resulting in a built-in electric field. Comparing to CrI₃and Nb₃Cl₈monolayers, the light absorption is enhanced in the infrared, visible and ultraviolet regions, and may hence improve the efficiency in energy conversion or optoelectronics. The rather narrow band gap hinders its application in water splitting, but may have potential applications related with infrared lights. Thus, the investigation provides theoretical insights for CrI₃/Nb₃Cl₈heterojunction and may promote its applications.

Understanding the temperature-dependent properties of intrinsic two-dimensional (2D) magnets is crucial for both fundamental research and technological applications. In this work, we employ nonlinear spin-wave theory, which incorporates magnon-magnon interactions, to evaluate the Curie temperature and spin-wave dispersions of several Cr- and Cu-based 2D magnets. We find that the resulting Curie temperatures are generally lower than those predicted by mean-field and linear-response approaches, yet they more closely match results obtained from accurate quantum Monte Carlo and random phase approximation methods, as well as experimental data. Our approach provides a robust and efficient computational framework for evaluating the corrected Curie temperature of 2D magnets.

The quality of neutron scattering studies relies upon accurately determined bound coherent neutron scattering lengthsb_c, whose standard tabulated values can be in need of review. We have measured integrated Bragg peak intensities via neutron diffraction from LiF powders, as well as scattering-length densities via neutron interferometry on LiF aqueous solutions, to accurately redetermine theb_cvalues for the lithium isotopes⁶Li and⁷Li, as well as that for naturally occurring elemental Li as a mix of these two isotopes. As compared to earlier studies going back to 1986, our measurements make use of considerably improved instrumentation, and careful attention was given to the experimental procedure as well as to data analysis, in particular to aspects of systematic error. From the neutron diffraction measurements we obtainb_c(⁶Li)_NPD= 2.27(2) fm,b_c(⁷Li)_NPD= -2.28(2) fm andb_c(^natLi)_NPD= -1.94(2) fm, in excellent agreement with our interferometry results ofb_c(⁶Li)_INT= 2.28(4) fm,b_c(⁷Li)_INT= -2.28(3) fm andb_c(^natLi)_INT= -1.93(3) fm, allowing to average them together and to propose recommended values ofb_c(⁶Li)_Rec. = 2.27(2) fm,b_c(⁷Li)_Rec. = -2.28(2) fm andb_c(^natLi)_Rec= -1.93(2) fm, where all values correspond to pure isotopes or the standard terrestrial isotopic composition of^natLi. Compared to standard literature values ofb_c(⁶Li)_Lit.= 2.0(1) fm,b_c(⁷Li)_Lit.= -2.22(2) fm, andb_c(^natLi)_Lit.= -1.90(3) fm, we note in particular that our recommended value forb_c(⁶Li) is 14% greater in magnitude, which is well outside of experimental uncertainties. Having obtained nearly identical results using two independent experimental techniques with qualitatively different possible sources of systematic error, we have confidence in our recommendedb_cvalues. We discuss reasons for the observed discrepancies with respect to previously tabulated values, as well as the relative merits of the various methods to measure bound coherent neutron scattering lengths.

We propose an algorithm for determining the zeros of the electric conductivity in large molecular nanonstructures such as graphene sheets. To this end, we employ the inverse graph method, whereby non-zeros of the Green's functions are represented graphically by a segment connecting two atomic sites, to visually signal the existence of a conductance zero as a line that is missing. In rectangular graphene structures the topological properties of the inverse graph determine the existence of two types of Green's function zeros that correspond to absolute conductance cancellations with distinct behavior in the presence of external disorder. We discuss these findings and their potential applications in some particular cases.

We investigated the thermally induced covalent coupling of cobalt porphyrin (CoP) molecules on an Au(111) surface using scanning tunnelling microscopy and first-principle calculations. While CoP molecules deposited at room temperature remain isolated due to electrostatic repulsion, annealing the substrate leads to their aggregation into chain-like structures with covalent bonding. Three distinct bonding motifs are identified, with calculations revealing weak magnetic coupling between theS=1/2Co ions. This work evidences a straightforward method for synthesising multinuclear complexes with magnetically coupled spins on surfaces, offering potential applications in molecular spintronics.

The plane-wave method with pseudopotentials has been the most widely used approach in solid-state electronic structure calculations. There is, however, usually a substantial gap from the fundamental physics to a practical code that could yield the detailed energy band structure for a solid. This review aims at giving a comprehensive introduction to the problem setting, fundamental strategy as well as various techniques involved in a typical plane-wave-based code. It starts from college quantum mechanics and ends up with some up-to-date topics such as the optimized norm-conserving Vanderbilt pseudopotential and the efficient diagonalization process of the Hamiltonian. It attempts to explain the mathematics and physics at the undergraduate level, and fundamental questions like 'why density functional theory', 'why plane wave basis' or 'why pseudopotential' are to be emphasized.

A novel phenanthrenyl-pyrenyl chalcone (PPC) dye was successfully designed and synthesized via the Claisen-Schmidt condensation method. In this molecular structure, the enone moiety serves as an efficientπ-bridge, connecting the phenanthrene donor to the pyrene substituents. The structural identity ofPPCwas confirmed through single-crystal x-ray diffraction analysis, which revealed the presence of intermolecular C-H···O hydrogen bonds andπ-πinteractions, forming a head-to-tail arrangement. These interactions play a crucial role in stabilizing the molecular framework and influencing its electronic properties. Hirshfeld surface analysis and 2D fingerprint plots were employed to quantitatively assess the intermolecular interactions withinPPC. The structural configuration ofPPCenables effective tuning of charge transfer characteristics and optical absorption properties, yielding a narrow energy gap of 2.77 eV. Preliminary findings indicate thatPPCholds significant potential as a dye sensitizer for DSSC applications, warranting further evaluation of its photovoltaic performance.