Interlayer Correlations Research Articles

Rigid-Rod Polyesters with Flexible Side Chains Based on 1,4-Dialkyl Esters of Pyromellitic Acid and 4,4‘-Biphenol. 7. Fluorescence Studies on Crystalline and Liquid Crystalline Layered Phases over a Wide Range of Temperatures

Rigid-rod polyesters with flexible side chains denoted as B-Cn form two types of layered crystals and two types of layered mesophases. These layered phases are characterized by a layered structure, in which the aromatic main chains are paced into a layer with the side chains occupying the space between the layers. The detailed aggregated structures for these two crystalline phases were studied by fluorescence spectroscopy, from which it was found that the ground-state charge-transfer complexes are formed between the biphenyl and pyromellitic moieties in the adjacent main chains and that these two moieties have an alternating lateral alignment inside a layer. Two layered crystals, K1 and K2, show charge-transfer fluorescence (475 and 505 nm) and its excitation spectra (400 and 425 nm) in different wavelengths, respectively. This difference in wavelengths is related to the difference in lateral packing distances (4.6 Å for K1 and 3.45 Å for K2 crystals) and suggested to be due to the distance between the electron-donating and -accepting units in the adjacent chains. In the isotropic phase, the charge-transfer bands were also observed. This result means that the isotropic state in this polymeric system can be defined by the state that a layered segregation is maintained, but the molecular ordering and the interlayer correlation are lost. It is well-known that the driving force of the adoption for layered structures is a segregation of aliphatic and aromatic domains. We have demonstrated here, moreover, that a charge-transfer interaction between the electron-donating and -accepting units in the neighboring main chains contributes to the organization of phase structures and spatial arrangements.

Radial distribution function analysis of the structure of activated carbons

The structure of a series of activated carbon materials prepared from a polymer of phenol formaldehyde resin with different degree of “burn-off” from 0 to 32% and variable porosity has been studied by wide-angle neutron scattering. The intensity measurements, extended to Q values of 50Å−1 yielded the radial distribution functions with the real space resolution of about 0.12Å. The obtained results show that the structural features of the investigated materials are not affected by the activation process. All well-defined peaks of the radial distribution functions can be reproduced by the model consisting of the defective graphite-like layers with weak inter-layer correlations.

Josephson Effects in Double-Layer Quantum Hall States

Under quite plausible assumptions on double-layer quantum Hall states with strong interlayer correlation, we show in general framework that coherent tunneling of a single electron between two layers is possible. It yields Josephson effects with unit charge tunneling. The origin is that Halperin states in the quantum Hall states are highly degenerate in electron number difference between two layers in the absence of electrons tunneling.

Roles of the interlayer spin correlations in the Cu NMR relaxation rates of bi- and tri-layered high-Tccuprates

The expressions for the Cu NMR relaxation rates $[{1/T}_{1}T, {(1/T}_{2G}{)}^{2}$, etc.] specific to the high-${T}_{c}$ cuprates with double and triple ${\mathrm{CuO}}_{2}$ layers (bi- and tri-layer systems) are discussed. In these systems, there can exist interlayer spin correlations between adjacent layers originating from the interlayer exchange coupling, besides that within each layer. The interlayer spin correlations manifest themselves as interlayer spin susceptibilities in the NMR relaxation rates. We found that in the bilayer systems, the interlayer susceptibility has a tendency to suppress ${1/T}_{1}T$. This is the opposite tendency to that in the ${(1/T}_{2G}{)}^{2}$ case reported so far, where ${(1/T}_{2G}{)}^{2}$ can be enhanced by the interlayer susceptibility. These features are important especially in the spin pseudogap $T$ regions in these systems. On the other hand, in the trilayer systems, the contribution of the interlayer susceptibility to ${(1/T}_{2G}{)}^{2}$ is negligible, because nuclear spins on the adjacent layers are unlike spins to each other. Based on the modified expressions for the relaxation rates, the spin pseudogap issues in these systems are discussed.

Determination of 2D Pair Correlations and Pair Interaction Energies of In Atoms in Molecular Beam Epitaxially Grown InGaAs Alloys

Intra- and interlayer atom-atom correlations in molecular beam epitaxially grown dilute InGaAs alloys were studied using cross-sectional scanning tunneling microscopy. By imaging individual chemical constituents we construct a large ensemble of ``atom maps'' from which two-dimensional In-In pair correlation functions were deduced. We found a total absence of interlayer pair correlation along $[001]$ and a strong negative correlation for the nearest neighbor (nn) pair along $[110]$, corresponding to a repulsive interaction energy of 0.1 eV for the nn In pairs along $[110]$. In addition, a weak long-range oscillation in the correlation function along $[110]$ is observed.

Phonon scattering in reflection high-energy electron diffraction: Multiple-scattering theory and experiment

A multiple-scattering formalism, based on the reflectivity matrix method of diffuse reflection high-energy electron diffraction (RHEED), is developed that allows us to calculate the electron-phonon scattering in RHEED due to correlated thermal vibrations for the case of one-phonon transitions. The scattering by the thermal displacements is calculated in first-order perturbation theory whereas the propagation of the diffusely scattered electrons in the periodic part of the scattering potential is treated exactly. The approach is particularly capable of treating the multiple electron scattering independently from the experimentally accessible and vibration dependent quantities. These quantities, the atomic displacement correlations, are described in terms of intralayer and interlayer correlation matrices, resolved with respect to the in-plane phonon momentum. Calculations for Pt(111) are presented and used to interpret experimentally obtained energy filtered streak profiles of the quasielastic thermal diffuse scattering (losses $<2\mathrm{eV}$). The general features of the phonon scattering are elucidated. Furthermore, the information depth and the influence of different atomic displacement directions on the diffuse intensities is investigated. An attempt is presented to ``measure'' the correlation matrices by means of an evaluation of the experimental data. The analysis produces good agreement between experiment and theory in conjunction with physically sensible correlation matrices that exhibit some specific properties expected for surfaces.

Ground state of a double-layer charged Bose system

The ground state of a double-layer charged Bose system is investigated beyond the random-phase approximation by including the many-body correlation effects. The correlations within the layer are accounted for within the self-consistent theory of Singwi, Tosi, Land, and Sj\"olander, while we have neglected the effect of interlayer correlations. The static susceptibility, the elementary excitation spectrum, and the static screened potentials are calculated and their dependence on the boson number density and the layer spacing is examined. Results are compared with the recent work of Tanatar and Das where correlations are not included. It is found that the inclusion of correlation effects combined with the interlayer interactions can significantly alter the nature of the ground state and, in particular, can favor an inhomogeneous charge-density-wave ground state. A comparison is also made in terms of screened potentials with the double-layer electron system that enables one to have a deeper insight into the role played by the exchange and Coulomb correlations separately.

Plasmon and shear modes in correlated superlattices

The dynamical matrix, dielectric response tensor, and dispersion relations for a strongly correlated unmagnetized superlattice are formulated in the quasilocalized charge approximation. Analysis of the dispersion relations at wavelengths long compared with the spacing d between adjacent layers indicates that the random-phase-approximation (RPA) collective-mode structure is substantially modified by particle correlations. In earlier works [see, e.g., G. Kalman, Y. Ren, and K. I. Golden, Phys. Rev. B 50, 2031 (1994)] the authors reported the existence of a long-wavelength energy gap in the acoustic plasmon band generated by strong interlayer correlations. The present analysis indicates the existence of a gapped shear mode band which is wholly maintained by Coulombic interlayer interactions over and above the RPA. When interlayer interactions are taken into account only through the average RPA field, the band collapses into a single shear mode which exhibits the long-wavelength acoustic dispersion characteristic of the correlated two-dimensional electron liquid. Other interesting effects include (i) an optical-phonon crystal-like dispersion exhibited by the in-phase plasmon at long wavelengths for d sufficiently small; and (ii) an acoustic-phonon dispersion exhibited by the in-phase shear mode at long wavelengths.

Interlayer coupling in the superconducting state ofBi2Sr2Ca2Cu3O10

Spin echo double resonance has been used to detect the spin-spin coupling between Cu spins on adjacent ${\mathrm{CuO}}_{2}$ layers. These measurements, performed in the superconducting state, on the three-layer Pb-doped bismuth high-${\mathrm{T}}_{\mathrm{c}}$ compound demonstrate the existence of interlayer exchange coupling as well as interlayer correlations in the quasiparticle excitations. An estimate of the interlayer exchange constant ${\mathrm{J}}_{\mathrm{\ensuremath{\perp}}}$ is found to be 43 K, 3% of the intralayer value.

Correlation effects in double quantum-well systems

An interacting double-layer electron system, with uniform positive backgrounds, is considered at finite temperatures and in the presence of a strong perpendicular magnetic field for integer filling factors. The low-energy physics of this system is described using an effective action formalism. The density-density correlation functions and the long-wavelength collective excitations of the electronic system (magnetoplasmons) are obtained. The results are valid beyond the random-phase approximation. Finally, the response of the system to electromagnetic interactions is considered and the current induced in one layer (transconductivity), when a current is driven only through the other layer, is evaluated. All results take into account explicitly interlayer and intralayer correlations.

Polarized neutron diffraction studies of antiferromagnetic EuTe/PbTe superlattices (abstract)

PbTe is a nonmagnetic semiconductor, and EuTe, also a semiconductor, is a type II fcc antiferromagnet below TN=10 K. Our earlier diffraction studies of [(EuTe)m|PbTe)3m]N samples (with m=2–7, N=200–600) showed that the type II ordering is preserved in the EuTe layers,1 but the lattice strain always selects an arrangement with the (111) ferromagnetic (FM) sheets (characteristic for the type II structure) parallel to the layers. In addition, samples with n⩽5 scans through the antiferromagnetic (AFM) maxima reveal pronounced patterns of satellite peaks—a clear signature of interlayer spin coherence, indicating that Eu–Eu interactions are transferred through PbTe barriers even as thick as 55 Å! The origin of this surprisingly long-range interaction cannot be understood on the grounds of the existing theories of interlayer coupling, in which high concentrations of conduction electrons always play a crucial role,2 because EuTe is insulating at low T and in PbTe n is as low as ∼1017 cm−3. In order to identify the coupling mechanism, we have begun new studies using polarized neutron diffraction. This technique is particularly useful for investigating the AFM domain arrangement. While the (111) symmetry allows six nonequivalent type II configurations, gradually increasing field should align all spins perpendicular to H, interfering with the coupling forces. Eventually, it should destroy the interlayer coherence—“monitoring” of this process may therefore reveal the much needed information about the interlayer coupling strength. Our experiments show a drastic differences in the system behavior depending on the “cooling history.” If the sample is cooled at H=0, then a modest field (∼0.5 T) indeed leads to the expected domain rotation. Further H increase induces a growing ferromagnetic component, and gradually suppresses the AFM one—however, the interlayer coherence in the AFM ordering can be still seen up to surprisingly high H values ∼5 T). On the other hand, if the sample is cooled through TN with the field on, then H as weak as 0.02 T already destroys the interlayer correlations. Explanation of the observed facts and estimates of the interaction strength based on model calculations will be presented, and some possible physical mechanisms undering the interlayer coherence (e.g., coupling by dipolar forces or coupling involving bound carrier states) will be discussed.

Magneto-oscillations of the tunnelling current between two-dimensional electron systems

The tunnelling current caused by electron transfer between two-dimensional layers is calculated as a function of the magnetic field applied perpendicular to the layers and level splitting of the tunnel-coupled states. The elastic scattering of the electrons is taken into consideration. Analytical results describing both the tunnelling relaxation rate of photoexcited electrons and the tunnelling current between the independently contacted quantum wells are obtained for two regimes: (i) that of small magnetic fields, for which the Landau quantization is suppressed by the scattering and the oscillating part of the current shows nearly harmonic behaviour; and (ii) that of high magnetic fields, for which the Landau levels are well defined and the current shows a series of sharp peaks corresponding to resonant magnetotunnelling. In the latter case, we used two alternative approaches: the self-consistent Born approximation method and the path-integral method, and demonstrated that the results obtained show reasonable agreement for both of these methods. The influence of the interlayer correlation of the scattering on the first magnetotunnelling peak is also discussed.

Local Structure of Ball-Milled Carbons for Lithium Ion Batteries: A Pair Distribution Function Analysis

ABSTRACTThe local atomic structure of ball-milled carbons was investigated by radial distribution function (RDF) analysis using pulsed time-of-flight neutron diffraction. The results exhibit a gradual loss of long-range order as a function of milling time. Modeling of the elastic structure factors and of the differential correlation functions identified the structure of ball-milled carbons as finite-size graphene fragments whose size decreases continuously with milling time. The large increase in lithium reversible capacity after 20 hours of milling was correlated with the loss of interlayer correlation between graphite flakes, similar to the structure of hard carbons in the “House of Cards” model.

Role of interlayer interactions on transition temperature in high- Tc cuprate superconductors

The effect of interlayer interactions on transition temperature in high- T c layered superconductors has been studied using a one-band two-layer tight binding Hamiltonian with intra- and interlayer attractive interactions. The double-time Green's function technique is employed and higher-order Green's functions are linearized by using a mean field decoupling approximation. The expressions for the transition temperature ( T c) and excitonic type interlayer correlation ( γ c) are obtained. It is shown that interlayer interactions play an important role in the enhancement of T c in high- T c cuprates. We have also explained the relevance of our results in high- T c layered superconductors having two layers per unit cell under externally applied pressure.

Plasmon dispersion in strongly correlated superlattices.

The dielectric response function of a strongly correlated superlattice is calculated in the quasilocalized charge (QLC) approximation. The resulting QLC static local-field correction, which contains both intralayer and interlayer pair-correlational effects, is identical to the correlational part of the third-frequency-moment sum-rule coefficient. This approximation treats the interlayer and intralayer couplings on an equal footing. The resulting dispersion relation is first analyzed to determine the effect of intralayer coupling on the out-of-phase acoustic-mode dispersion; in this approximation the interlayer coupling is suppressed and the mutual interaction of the layers is taken into account only through the average random-phase approximation (RPA) field. In the resulting mode dispersion, the onset of a finite-k (k being the in-plane wave number) reentrant low-frequency excitation developing (with decreasing d/a) into a dynamical instability is indicated (a being the in-plane Wigner-Seitz radius and d the distance between adjacent lattice planes). This dynamical instability parallels a static structural instability reported earlier both for a bilayer electron system and a superlattice and presumably indicates a structural change in the electron liquid. If one takes account of interlayer correlations beyond the RPA, the acoustic excitation spectrum is dramatically modified by the appearance of an energy gap which also has a stabilizing effect on the instability. We extend a previous energy gap study at k=0 [G. Kalman, Y. Ren, and K. I. Golden, Phys Rev. B 50, 2031 (1994)] to a calculation of the dispersion of the gapped acoustic excitation spectrum in the long-wavelength domain. \textcopyright{} 1996 The American Physical Society.

Correlations, compressibility, and capacitance in double-quantum-well systems in the quantum Hall regime.

In the quantum Hall regime, electronic correlations in double-layer two-dimensional electron systems are strong because the kinetic energy is quenched by Landau quantization. We point out that these correlations are reflected in the way the partitioning of charge between the two layers responds to a bias potential. We report on illustrative calculations based on an unrestricted Hartree-Fock approximation, which allows for spontaneous interlayer phase coherence. The possibility of studying interlayer correlations by capacitive coupling to separately contacted two-dimensional layers is discussed in detail. \textcopyright{} 1996 The American Physical Society.

Diffusion Monte Carlo Study of Electrons in Two-dimensional Layers

We investigate the phase diagram of electrons in two dimensions at T = 0 by means of accurate diffusion Monte Carlo simulations within the fixed-node approximation. At variance with previous studies, we find that in an isolated layer Slater-Jastrow nodes yield stability of the fully polarised fluid at intermediate coupling, before freezing into a triangular crystal sets in. We have also studied coupled layers of electrons and of electrons and holes. Preliminary results show that at large coupling, as two layers are brought together from infinity, inter-layer correlation first stabilises the crystalline phase at distances of the order of the in-plane inter-particle spacing. As the distance is further decreased the effect of correlation, as expected, turns into an enhanced screening, which disrupts the crystalline order in favour of liquid phases.

Phase Structure and Polymorphism of n-Alkyl Monoesters of Biphenyl-4,4′-dicarboxylic Acid

Abstract The phase structure of the n-alkyl monoesters of biphenyl-4,4′-dicarboxylic acid has been investigated using optical microscopy and X-ray diffraction techniques. A polymorphism N, SC' SF and crystal B has been found which is understandable because of the essentially 2-d correlated smectic F phase with only a small interlayer correlation and the extensive 3-d correlation of the smectic B phase. The formation of dimers via H-bridges and an intercalation of the dimers which is active within the first 4 to 5 CH2 groups of the tail groups of the dimers in both ends have been proven by X-ray diffraction.

Skeletonization as a Probe of Interlayer Correlations in Langmuir−Blodgett Films

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTSkeletonization as a Probe of Interlayer Correlations in Langmuir−Blodgett FilmsM. L. Kurnaz and D. K. SchwartzView Author Information Department of Chemistry, Tulane University, New Orleans, Louisiana 70118 Cite this: Langmuir 1996, 12, 20, 4971–4975Publication Date (Web):October 2, 1996Publication History Received8 March 1996Revised2 July 1996Published online2 October 1996Published inissue 1 January 1996https://doi.org/10.1021/la960214nCopyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views54Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (387 KB) Get e-AlertsSUBJECTS:Layers,Monolayers,Thin films,Vesicles,pH Get e-Alerts

Interlayer correlation of Fe spins and charges in the 2-D triangular ferrimagnet ErFe 2O 4

Neutron polarization analysis was applied to Bragg lines at (⅓, ⅓, l) and (⅔, ⅔, l) of an ErFe 2O 4 single crystal at 15 K. The magnetic scattering intensity is composed of three sinusoidal curves, corresponding to the spin correlations between next-nearest-neighbor Fe Fe or Fe Er layers. The correlation length along the c-axis is only about 8 Å, in contrast to 50 Å in the c-plane. The nuclear part of the scattering indicates correlation of atomic displacements up to about 50 Å along the c-axis, independent of the spin ordering.