Presence Of Lattice Distortions Research Articles

Effect of lattice distortion on spin admixture and quantum transport in organic devices with spin–orbit coupling

Abstract With an extended Su–Schrieffer–Heeger model and Green’s function method, the spin–orbit coupling (SOC) effects on spin admixture of electronic states and quantum transport in organic devices are investigated. The role of lattice distortion induced by the strong electron–lattice interaction in organics is clarified in contrast with a uniform chain. The results demonstrate an enhanced SOC effect on the spin admixture of frontier eigenstates by the lattice distortion at a larger SOC, which is explained by the perturbation theory. The quantum transport under the SOC is calculated for both nonmagnetic and ferromagnetic electrodes. A more notable SOC effect on total transmission and current is observed for ferromagnetic electrodes, where spin filtering induced by spin-flipped transmission and suppression of magnetoresistance are obtained. Unlike the spin admixture, a stronger SOC effect on transmission exists for the uniform chain rather than the organic lattices with distortion. The reason is attributed to the modified spin-polarized conducting states in the electrodes by lattice configuration, and hence the spin-flip transmission, instead of the spin admixture of eigenstates. This work is helpful to understand the SOC effect in organic spin valves in the presence of lattice distortion.

Spin-orbital mechanisms for negative thermal expansion in Ca2RuO4

The phenomenon of negative thermal expansion (NTE) deals with the increase of the lattice parameters and the volume of the unit cell when the material is thermally cooled. The NTE is typically associated with thermal phonons and anomalous spin-lattice coupling at low temperatures. However, the underlying mechanisms in the presence of strong electron correlations in multiorbital systems are not yet fully established. Here, we investigate the role of Coulomb interaction in the presence of lattice distortions in setting out the NTE effect, by focusing on the physical case of layered ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ with the ${d}^{4}$ configuration at each Ru ion site. We employ the Slater-Koster parametrization to describe the electron-lattice coupling through the dependence of the d-p hybridization on the Ru-O-Ru bond angle. The evaluation of the minimum of the free energy at finite temperature by fully solving the multiorbital many-body problem on a finite-size cluster allows us to identify the regime for which the system is prone to exhibit NTE effects. The analysis shows that the nature of the spin-orbital correlations is relevant to drive the reduction of the bond angle by cooling, and in turn the tendency toward a NTE. This is confirmed by the fact that a changeover of the electronic and orbital configuration from ${d}^{4}$ to ${d}^{3}$ by transition metal substitution is shown to favor the occurrence of a NTE in ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$. This finding is in agreement with the experimental observations of a NTE effect which is significantly dependent on the transition metal substitution in the ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ compound.

Realizing Interfacial Electron/Hole Redistribution and Superhydrophilic Surface through Building Heterostructural 2nm Co0.85 Se-NiSe Nanograins for Efficient Overall Water Splittings.

Electrochemical overall water splitting using renewable energy input is highly desirable for large-scale green hydrogen generation, but it is still challenged due to the lack of low-cost, durable, and highly efficient electrocatalysts. Herein, 1D nanowires composed of numerous 2nm Co0.85 Se-NiSe nanograin heterojunctions as efficient precious metal-free bifunctional electrocatalyst are reported for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution with the merits of high activity, durability, and low cost. The abundant microinterface among the ultrafine nanograins and the presence of lattice distortion around nanograin interface is found to create a superhydrophilic surface of the electrocatalyst, which significantly facilitate the fast diffusion of electrolytes and the release of the formed H2 and O2 from the catalyst surface. Furthermore, synergic effect between Co0.85 Se and NiSe grain on adjusting the electronic structure is revealed, which enhances electron mobility for fast electron transport during the HER/OER process. Owing to these merits, the rationally designed Co0.85 Se-NiSe heterostructures display efficient overall water splitting behavior with a low voltage of 1.54V at 10mAcm-2 and remarkable long-term durability for the investigated period of 50h.

Multiple spin-orbit excitons in \u03b1-RuCl3 from bulk to atomically thin layers

The van der Waals Kitaev magnet α-RuCl3 has recently garnered considerable attention due to its possible realization of topological spin liquids. Combining Raman spectroscopy with numerical calculations, we report here the thickness dependence of electronic structure and ensuing low-energy excitations for exfoliated α-RuCl3. We observe two pronounced peaks at A1 = 249 meV and A2 = 454 meV, which are assigned to single and double spin-orbit (SO) excitons, respectively. Our numerical calculations support this interpretation by reproducing their spectral energy and shape with the electronic parameters: SO coupling λ = 140 meV, Hund’s coupling JH = 350 meV, and on-site Coulomb interaction U = 2.35 eV. The multiple SO excitons persist down to a single layer, whereas their peaks shift slightly to lower energy. For frequencies below 350 cm−1, both a magnetic continuum and phonons show noticeable thickness dependence. These results demonstrate that a SO entangled jeff = 1/2 picture remains valid in a monolayer limit despite the presence of lattice distortions.

Wormhole-like mesoporous magnesium oxide fabricated by surfactant templating method to enhance cycling performance of lithium-sulfur batteries

Lithium-sulfur (Li–S) batteries are considered to have the best development prospect for electric vehicles. But enhancing the cycling performance of Li–S batteries is necessary and urgent. Mesoporous MgO particles (MMgO) are prepared by surfactant templating method and used to prepare cathode materials for the first time. The prepared MMgO has a hexagonal flake-like structure with a thickness of 50–80 nm, a transverse length of 150–350 nm, a processing area of 181.56 m2/g, an average pore diameter of 3.11 nm and a pore volume of 0.26 cc/g. MMgO shows low intensity and slightly broader diffraction peaks in the XRD pattern, indicating the presence of lattice distortion, defects, dislocations or unsaturated valence bonds. MMgO particles are uniformly distributed on the sulfur surface to provide high surface area, many active sites and interconnected channel structure, which makes more sulfur contact with MMgO to be adsorbed, activated and participated in charge and discharge reaction. The Li–S battery containing sulfur/MMgO composite at weight ratio 90:10 shows the best cyclic stability with capacity retention rate 84.7% after 100 cycles at 0.2 C. The initial specific capacity of a Li–S battery with sulfur/MMgO composite at weight ratio 70:30 can reach 1062 mAh/g at 0.2 C, which is much higher than sulfur/commercial MgO at the same weight ratio.

The direction of the d-vector in a nematic triplet superconductor

We investigate the states of triplet pairing in a candidate nematic superconductor versus typical material parameters, using the mean field theory for two- and three-dimensional tight-binding models with local triplet pairing in the Eu representation of the D3d, the point group of the system. In the two-dimensional model, the system favors the fully gapped chiral state for weaker warping or lower filling level, while a nodal and nematic state is favorable for stronger warping or higher filling, with the d-vector aligned along the principle axis. In the presence of lattice distortion, relative elongation along one of the principle axes, , tends to rotate the nematic d-vector orthogonal to , resulting in the nematic state at sufficient elongation. Three-dimensionality is seen to suppress the chiral state in favor of the nematic ones. Our results may explain the variety in the probed direction of the d-vector in existing experiments.

Micro- and nano-scale study of deformation induced mineral transformations in Mg-phyllosilicate-rich fault gouges from the Galera Fault Zone (Betic Cordillera, SE Spain)

Naturally and experimentally deformed gouges from sliding surfaces within the Galera Fault Zone were analyzed using scanning and transmission electron microscopy (SEM, TEM) to identify changes in the fault rocks as a consequence of ongoing deformation. The two gouges studied have a particular mineral association that includes planar (mainly smectite and illite) and fibrous clay minerals (sepiolite and palygorskite). Microstructural findings include a radical difference in grain alignment between the two gouges, a phenomenon that strongly influences gouge permeability. Smectite crystals are aligned on the same orientation and show a great number of layer terminations and delamination on the basal planes that contribute to a distributed mode of deformation in the gouge. In contrast, the sepiolite-rich gouge exhibits a grid-like microfabric that results in localized deformation limited to small areas where the needle-like crystals are bent and broken producing “feather-like” structures, without the presence of lattice distortions. Meanwhile, significant chemical results include: (1) Al content identified in sepiolite fibers through analytical electron microscopy (AEM), together with variability in the (110) d-spacing of sepiolite across single fibers, suggest the existence of a progressive transformation from sepiolite to palygorskite. (2) Mg content in smectite suggests that a portion of the smectites within the fault plane could have an authigenic origin and may be the result of a transformation reaction from palygorskite, however, the similarity of the 2:1 layer compositions between the smectites in the two contexts do not allow to either confirm nor deny such possibility. (3) Chemical continuity of Mg-decrease and Al+Fe-increase in the octahedral cation content of the sepiolites, palygorskites, and smectites within the gouges indicate a sequence of mineral transformations that is favored by a depleted Mg content and an increase of Al content in the fluid. In this setting, deformation promotes grain size reduction and fluid-rock interaction with the wall rocks resulting in a local supply of Al to the fault gouge that drives phase transformations. Structural differences between smectites and fibrous clay minerals affect important chemical and physical properties of the gouge including their mechanical properties. We propose that the permeability of the gouges in the Galera Fault is strongly affected by their mineralogy. Furthermore, the extent of the mineral authigenesis and mineral transformations could be a controlling factor that progressively changes both the permeability and the strength of the fault.

Influence of Li co-doping on structural property of sol-gel derived terbium doped zinc oxide nanoparticles

The presence of lattice distortion and defects in a composition leads towards a significant change in the optical, magnetic and electrical properties of the host material. In the present work, we have investigated the role of Li concentrations (0.25–1.0%) on structural property of Tb (1%) doped zinc oxide nanoparticles. A small concentration of terbium (1%) has been used to get minimum lattice distortion in the original structure of ZnO. To reduce the possible large lattice deformation on doping of Tb ion we have co-doped the material with Li. The crystalline nature of the sample has been confirmed by the XRD, Raman and FTIR studies of the material. The variation of bond length and lattice disorder in ZnO lattice due to the substitution of Tb and Li were studied from the EXAFS analysis at Zn K edge and Tb L3 edge. Interestingly, the study also shows that disorder decreases due to co-doping of Li in the considered system. Moreover, the oxidation states of all the elements present in the prepared samples were ascertained the XANES analysis. The morphology and particle size are calculated by TEM characterization. This work mainly emphasises on the structural property of synthesized compositions using these analyses. The study will also be helpful in exploring the change in optical, magnetic and electrical properties of the doped ZnO nanoparticles.

Spectral Properties and Stability in the Two-Dimensional Lattice-Hubbard Model

The two-dimensional Hubbard model on the square lattice is studied in the presence of lattice distortions in the adiabatic approximation. The self energy is computed within perturbation theory up to second order, which provides a way for studying the quasiparticle dispersion. We compute numerically the second order contribution to the self-energy using a standard fast Fourier transform algorithm for finite sizes system. The stability of the lattice distortions is investigated and a schematic phase diagram is drawn. The Fermi surface is analyzed for densities close to half filling, the presence of lattice distortions changes some spectral properties of the model and gives an anisotropic interacting Fermi surface. The spectral function is calculated along several lines in momentum space and the renormalized quasiparticle dispersion is obtained. The behavior of the density of states is shown for different values of the intrasite repulsion U in the different phases.

Orbital Ordering and Jahn-Teller Distortion in Perovskite RuthenateSrRuO3

Local density approximation plus on-site Coulomb interaction U band structure calculations reveal that SrRuO3 exhibits a half-metallic ground state with an integer spin moment of 2.0 microB/SrRuO3. An associated tilting 4dt2g orbital ordering on a Ru sublattice is observed under the on-site Coulomb interaction U in the presence of lattice distortion. This finding unravels the on-site Coulomb correlation as the driving force of the 4d orbital ordering and Jahn-Teller distortion as well as of the half-metallic ground state.

Evaluation of lattice distortion near c-ZrO2/α-Al2O3 interface by plasmon loss

Plasmon energies near a cubic-ZrO2 (c-ZrO2)/α-Al2O3 interface were studied by electron energy loss spectroscopy using a field-emission transmission electron microscope. The plasmon energies measured by scanning an electron probe of 1 nm in diameter across the interface showed that, approaching the interface, the plasmon energy of c-ZrO2 increases from 23.9 to 24.3 eV and that of α-Al2O3 decreases from 24.3 to 23.4 eV. Energy dispersive x-ray spectroscopy revealed that fluctuation of the chemical composition across the interface is small (⩽5%) and causes only a slight change in the plasmon energies (⩽0.16 eV). We conclude that the large energy changes (up to 0.9 eV) are mainly caused by lattice distortion. Using the Drude model, it was found that, 3 nm from the interface, the unit cell volume of c-ZrO2 decreases by 3% and that of α-Al2O3 increases by 6% compared with the volumes at 50 nm. The presence of lattice distortion near the interface was also confirmed by the convergent-beam electron diffraction method. The results show that plasmon loss is useful to evaluate lattice distortion.

Role of lattice distortions in the transport property of R0.7Me0.3MnO3 (R=Pr,Nd,La and Me=Ba,Sr,Ca) (abstract)

There are different models which to try to explain the transport properties of the manganese oxides in terms of magnetic polarons, Zener double exchange and Jahn-Teller distortions of the lattice which is temperature dependent. Using Rutherford backscattering techniques (2–3 MeV He ions) we are measuring the presence of lattice distortions by studying the angular scans in the channeling mode. The angular widths (FWHM) can be used to extract both dynamic and static displacements of the atoms from their equilibrium sites. The technique is extremely powerful in the sense that local uncorrected displacements as small as 0.01 Å from the equilibrium position can be detected. The extraction of the physics from the data is relatively straight forward compared to other techniques such as XRD or neturon scattering. Using a variable temperature backscattering system at our center (one of three or four systems around the world) the angular width (FWHM) is found to exhibit a dramatic change with temperature increasing with decreasing temperature showing a possible correlation with both the transport and magnetic properties. The results suggest a decrease in the lattice disorder with reduced temperature far in excess of what one would predict on the basis of a simple Debye behavior. The reduction in the lattice disorder correlates very well with the resistance vs temperature dependence. A variety of manganese oxide epitaxial thin films grown by pulsed laser deposition have been studied and the data suggests a role for structural distortions in any mechanism to explain the transport properties of these materials.

Transmission electron microscope study of II–VI/III–V semiconductor interfaces

Structures of ZnSe/GaAs epitaxial interfaces have been studied by cross-sectional transmission electron microscopy. Narrow dark bands are observed along these interfaces in their bright field and high resolution electron microscope images, suggesting a certain form of modifications of the structure. Despite the appearance of the dark hands, perfect coherent lattice structures are observed in high resolution images of the interfaces. Weak beam dark field images indicate the presence of lattice distortions in the neighborhood of the interfaces. These observations are explained by assuming the existence of a thin interface layer which maintain the coherent lattice relation with matrix crystals. As-grown and annealed ZnSe/GaAs epitaxial interfaces are compared in order to investigate the structural origin of the change of the electrical property of the interface by the post-growth annealing. The observation suggests that the interfacial layer remains after annealing but has changed into a slightly broader one.

Low temperature electron microscopy on the cubic-tetragonal transformation of V3Si

The cubic-tetragonal martensitic transition of V3Si and its precursor have been investigated in the temperature range from 13 K to 80 K using a 1 MV electron microscope with a double-tilting cold stage. Below the transition temperature Tm = 19 K, fine twin lamellae appear parallel to {110} plane traces, being connected continuously with mottled striations having the same orientation. Fine striations along {110} traces or so-called tweeds are observed below 50 K at the precursor of the structural phase transition. The image contrast of mottled striations and tweed patterns is attributed to the presence of lattice distortion owing to the softening of the shear modulus. Reversible changes of the patterns recorded with a TV-VTR system during cooling and heating processes were discussed briefly.

Dimerization and Solitons in One-Dimensional XY-Z Antiferromagnets

Our previous calculations of the lattice distortion and the formation energy of a soliton in the one-dimensional antiferromagnetic Heisenberg spin-Peierls systems are refined and extended to the case of X Y - Z model. The spin degree of freedom are represented by the phase Hamiltonian with the help of boson representation of fermions introduced by the Jordan-Wigner transformation. Parameters in this phase Hamiltonian are adjusted so that spin wave velocity and exponent of correlation function agree with exact results. This adjustment is shown to give also exact spin susceptibility in the absence of lattice distortion. Based on this phase Hamiltonian of the X Y - Z model localized excitations (solitons) in the presence of lattice distortions are examined in details including the width, the formation energy and the magnetic field dependence.

Effect of Lattice Distortion on Electron—Impurity Scattering Phase Shifts in the Distorted‐Wave Born Approximation

AbstractThe effect of lattice distortion on electron—impurity scattering is estimated using the distorted‐wave Born approximation for phase shifts. For weak impurity scattering the phase shift for the scattering complex is the sum of the phase shifts from the point impurity and the lattice strain field. Model calculations show that there may be important corrections to this picture when the magnitudes of the impurity phase shifts are about π/10 or larger. These corrections arise from backscattering of electrons by the distortion field surrounding the impurity. It is concluded that one may incur appreciable error in calculating pseudopotentials or impurity phase shifts in the presence of lattice distortion if one does not include the lattice backscattering effect discussed in this paper.

Dimensional Hume-Rothery factor and shear stability of bcc solid solutions

The relation between the elastic shear constants and the dimensional Hume-Rothery factor is traced on the basis of the pseudopotential method for a number of bcc solid solutions AB. It is clarified that in the case of a substantial difference between the atomic volumes ωA and ωB, the constant c′=(c11-c12)/2 takes on anomalously low values and even vanishes. The conclusion is hence made that the explanation of the 15% Hume-Rothery rule is possible from the aspect of stability of the crystalline lattice to shear. The presence of lattice distortion is not needed here in principle, as had been assumed earlier. It is shown that ordering of atoms according to the CsCl type can result in an abrupt increase in the value of c′, i.e., in stabilizing the lattice of the initial disordered solid solution.

Paracrystalline Structure of Polymer-Crystal Lattice Distortion Induced by Electron Irradiation

The melting temperature of polyethylene crystals decreases and the lattice constants (both a and b) and lattice distortion increase, but the macroscopic volume of the specimen does not change with electron irradiation. From these results a model of a deformed lattice structure with point defects produced by irradiation is proposed. Calculations indicate that the anisotropy of a polymer crystal (difference between the elastic modulus along the molecular axis and perpendicular to the axis) increases the range of the distortion in a crystal caused by a defect. The presence of lattice distortion in electron irradiated polymer single crystals produces observable features in the Moiré patterns obtained from the crystals.