Materials Literature
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We investigate the spectral function of a hole moving in the orbital-ordered ferromagnetic planes of LaMnO3, and show that it depends critically on the type of orbital ordering. While the hole does not couple to the spin excitations, it interacts strongly with the excitations of e(g) orbitals (orbitons), leading to a…
Microscopic phase segregation by chemical doping and resultant anomalous dielectric response have been investigated for tetrathiafulvalene-p-chloranil complex doped with trichloro-p-benzoquinone ( QCl3). Beyond a critical QCl3 content, the system shows a behavior of relaxor ferroelectrics, as characterized by strong f…
The vibrational density of states of single-wall carbon nanotubes (SWNT) was obtained from inelastic neutron scattering data from 0 to 225 meV. The spectrum is similar to that of graphite above 40 meV, while intratube features are clearly observed at 22 and 36 meV. An unusual energy dependence below 10 meV is assigned…
By including the contributions of dipolar defects in the time-dependent Ginzburg-Landau theory, we have simulated the domain switching process in ferroelectrics. The model incorporates elastic effects in the form of an anisotropic long-range interaction that is obtained by integrating out the strain fields, subject to…
Photoluminescence (PL) from mesoporous silica (MS) with the pore size of ∼6 nm and the thickness of walls among pores of ∼1 nm has been studied at room temperature. The heat pretreatment of MS in air at different temperatures and the variation of the excitation wavelengths allow one to shift the PL peak through the wh…
The metal–insulator transition and underlying spin dynamics in La0.7D0.3MnO3 (D=Ca, Sr) are investigated using optical pump–probe spectroscopy at 1.5 eV. Our measurements, which span the ferromagnetic–paramagnetic transition temperature, reveal that the dynamics of the optically induced spectral weight transfer follow…
The reactivity of different carbon–nitride structures has been studied using density functional theory calculations. The studies involve C59N and clusters of curved and planar CNx structures. Nitrogen is shown to lower the energy of pentagon defects in the graphite like structures, whereas heptagons are unlikely to be…
We extend the method for the formulation of selection rules for high harmonic generation spectra [Phys. Rev. Lett. 80, 3743 (1998)] beyond the dipole approximation and apply it to single-walled carbon nanotubes interacting with a circularly polarized laser field. Our results show that the carbon nanotubes can be excel…
A 0.4 μm long semiconducting single-walled carbon nanotube is doped into n type by potassium (K) vapor. Electrical measurements of the doped nanotube reveal single-electron charging at temperatures up to 160 K. The K-doped sample manifests as a single quantum dot or multiple quantum dots in series depending on the ran…
We have made Meservey-Tedrow style spin-polarized tunneling measurements on ${\mathrm{SrRuO}}_{3}$, using a ${\mathrm{SrTiO}}_{3}$ barrier. In contrast to all other materials measured with this technique, we found the spin polarization to be negative, $P\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}…
Can one construct a thermodynamics for compact, slowly moving powders and grains? A few years ago, Edwards proposed a possible step in this direction, raising the fascinating perspective that such systems have a statistical mechanics of their own, different from that of Maxwell, Boltzmann, and Gibbs, allowing us to ha…
A Comment on the Letter by H. Hakkinen, R. N. Barnett, and U. Landman, Phys. Rev. Lett. 82, 3264 (1999).
In the literature, the electric modulus representation has been used to provide comparative analysis of the ion transport properties in different ion-conducting materials. In this paper we show that the modulus representation is not a suitable tool for such purposes. Our arguments derive from an examination of the sca…
The electronic structure of graphitic cones exhibits distinctive topological features associated with the apical disclinations. Ahranov-Bohm magnetoconductance oscillations (period Phi(0)) are completely absent in rings fabricated from cones with a single pentagonal disclination. Close to the apex, the local density o…
For the case of finite life-time broadening the standard Kubo-formula for the optical conductivity tensor is rederived in terms of Green's functions by using contour integrations, whereby finite temperatures are accounted for by using the Fermi-Dirac distribution function. For zero life-time broadening, the present fo…
We argue that in lightly hole doped perovskite-type Mn oxides the holes $({\mathrm{Mn}}^{4+}$ sites) are surrounded by nearest neighbor ${\mathrm{Mn}}^{3+}$ sites in which the occupied $3d$ orbitals have their lobes directed towards the central hole $({\mathrm{Mn}}^{4+})$ site and with spins coupled ferromagnetically…
The contour integration technique applied to calculate the optical conductivity tensor at finite temperatures in the case of layered systems within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker band structure method is improved from the computational point of view by applying the Gau…
We show that the observed transition from rock salt to orthorhombic P(nma) symmetry in CrN can be understood in terms of stress anisotropy. Using local spin density functional theory, we find that the imbalance between stress stored in spin-paired and spin-unpaired Cr nearest neighbors causes the rock-salt structure t…
The contour integration technique applied to calculate the optical conductivity tensor at finite temperatures in the case of inhomogeneous surface layered systems within the framework of the spin-polarized relativistic screened Korringa-Kohn-Rostoker band structure method is extended to arbitrary polarizations of the…
In tunnel junctions of which at least one side is a ferromagnet, very large magnetic polarization change ($\approx 0.1 μ_B$) and splitting of the spin up and spin down Fermi energy ($\approx 0.1 eV$) can be created under steady state finite current conditions (bias voltage $\approx$ 1 volt). This is {\bf much higher}…