Physical review. B, Condensed matter

Nowadays, ground stations which integrate the control segment of a satellite mission have as a common feature, the use of large reflector antennas for space communication. Apart from many advantages, large dishes pose a number of impairments regarding their mechanical complexity, low flexibility, and high cost. In the user segment, the use of planar arrays to substitute domestic reflectors will p…

The standard definition of a spin current, applied to the conductors lacking inversion symmetry, results in nonzero spin currents. I demonstrate that the spin currents do not vanish even in thermodynamic equilibrium, in the absence of external fields. These currents are dissipationless and are not associated with real spin transport. The result should be taken as a warning indicating problems inh…

We show that carbon nanotube Schottky-barrier transistors exhibit scaling that is qualitatively different than conventional transistors. The performance depends in an unexpected way on both the thickness and the dielectric constant of the gate oxide. Experimental measurements and theoretical calculations for ambipolar devices provide a consistent understanding of the novel scaling, which reflects…

Neutron scattering has been used to investigate the crystal structure and lattice dynamics of superconducting ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_{2}\ensuremath{\cdot}1.4(\mathrm{H}/\mathrm{D}{)}_{2}\mathrm{O},$ and the ``parent'' ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_{2}$ material. The structure of ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_{2}$ consists of alternate layers of ${\mathrm{CoO}}_{2}$ and Na an…

Neutron and x-ray powder diffraction have been used to investigate the crystal structures of a sample of the newly-discovered superconducting sodium cobaltate deuterate compound with composition ${\mathrm{Na}}_{0.31(3)}{\mathrm{CoO}}_{2}\ensuremath{\cdot}1.25(2){\mathrm{D}}_{2}\mathrm{O}$ and its anhydrous parent compound ${\mathrm{Na}}_{0.61(1)}{\mathrm{CoO}}_{2}.$ The anhydrous parent compound …

We investigate the electrical injection of spin-polarized electrons into a semiconductor [Al(GaAs)] heterostructure from ferromagnetic FeCo metal through an ${\mathrm{AlO}}_{x}$ tunnel barrier. We have developed the optical oblique Hanle effect approach for the quantitative analysis of electrical spin injection into semiconductors. This technique is based on the manipulation of the electron spins…

We measure the effects of phonon confinement on the Raman spectra of silicon nanowires. We show how previous spectra were inconsistent with phonon confinement, but were due to intense local heating caused by the laser. This is peculiar to nanostructures, and would require orders of magnitude more power in bulk Si. By working at very low laser powers, we identify the contribution of pure confineme…

The crystal structure, lattice strain due to the antiferromagnetic ordering, and magnetic form factor in the itinerant $5f$ compounds $\mathrm{U}T{\mathrm{Ga}}_{5}(T=\mathrm{N}\mathrm{i},\mathrm{}\mathrm{P}\mathrm{d},\mathrm{}\mathrm{Pt})$ have been studied by neutron scattering. High-resolution powder diffraction revealed that the tetragonality of the U-Ga layers increases down to the series of …

We systematically investigate lensing of electromagnetic waves by a negative refractive-index material slab constructed from a two-dimensional photonic crystal with properly designed equifrequency-surface configuration [Luo et al., Phys. Rev. B 65, 201104 (2002)]. We find that a point source placed in the vicinity of the slab can form a good-quality image in the opposite side of the slab. However…

The carrier concentration dependence of the interaction between free carriers and longitudinal optical (LO) phonons of InN is studied by Raman scattering and Fourier transform infrared measurements. InN is grown on a sapphire (0001) surface by plasma-assisted molecular beam epitaxy. The carrier concentration is varied from $1.8\ifmmode\times\else\texttimes\fi{}{10}^{18}$ to $1.5\ifmmode\times\els…

Transport through molecular quantum dots coupled to a single vibration mode is studied in the case with strong coupling to the leads. We use an expansion in the correlation between electrons on the molecule and electrons in the leads, and show that the tunneling broadening is strongly suppressed by the combination of the Pauli principle and the quantization of the oscillator. As a consequence the…

Transport through molecular devices with strong coupling to a single vibrational mode is considered in the case where the vibration is damped by coupling to the environment. We focus on the weak tunneling limit, for which a rate equation approach is valid. The role of the environment can be characterized by a frictional damping term $\mathcal{S}(\ensuremath{\omega})$ and a corresponding frequency…

We present measurements of the transmission of terahertz radiation through periodic arrays of holes made in highly doped silicon wafers. The size of the holes, $70\ifmmode\times\else\texttimes\fi{}70\ensuremath{\mu}\mathrm{m},$ is significantly smaller than the radiation wavelength $\ensuremath{\lambda}\ensuremath{\simeq}500\ensuremath{\mu}\mathrm{m}.$ Sharp resonances and enhanced transmissions …

We give three methods for entangling quantum states in quantum dots. We do this by showing how to tailor the resonant energy (F\"orster-Dexter) transfer mechanisms and the biexciton binding energy in a quantum dot molecule. We calculate the magnitude of these two electrostatic interactions as a function of dot size, interdot separation, material composition, confinement potential, and applied ele…

Donor electron spins in phosphorus-doped silicon (Si:P) are a candidate two-level system (qubit) for quantum information processing. Spin echo measurements of isotopically purified ${}^{28}\mathrm{S}\mathrm{i}:\mathrm{P}$ are presented that show exceptionally long transverse relaxation (decoherence) times, ${T}_{2},$ at low temperature. Below $\ensuremath{\sim}10\mathrm{K}$ the spin decoherence i…

We have adapted the microscopic theory of nucleation for the epitaxial growth of inorganic materials to the nucleation of organic small molecules on an inert substrate like the gate dielectric of an organic thin-film transistor. The parameters required to explore the model were calculated with the standard MM3 force field and also include experimentally determined vapor pressure data, as well as …

Using high-resolution angle-resolved photoemission spectroscopy on ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}},$ we observe a new mass renormalization or ``kink'' in the E vs $\stackrel{\ensuremath{\rightarrow}}{k}$ dispersion relations localized near $(\ensuremath{\pi},0).$ The resolution of bilayer splitting allowed the first direct measurements of…

We present a first-principles electronic band structure for pure ${\mathrm{LiFePO}}_{4},$ delithiated ${\mathrm{FePO}}_{4},$ and Cr-doped ${\mathrm{LiFePO}}_{4}.$ It indicates that not only Fe but also O atoms are oxidized in the delithiation process, while P is little affected. This is in contrast to the usual view of the intercalation reaction that the removal of Li only transforms Fe from ${\m…

We show that the Uemura relation, namely ${T}_{c}$ proportional to superfluid density ${\ensuremath{\rho}}_{s},$ is not generally satisfied in high-${T}_{c}$ superconductors. Instead, a modified plot of ${T}_{c}/{\ensuremath{\Delta}}_{0}$ versus ${\ensuremath{\rho}}_{s}$ where ${\ensuremath{\Delta}}_{0}$ is the maximum d-wave gap at $T=0,$ exhibits universal features that point to an alternative …