An Electronic Model for CoO2CoO_2 layer based systems: Chiral RVB metal and Superconductivity

Takada et al. have reported superconductivity in layered Na__x CoO_2.yH_2O ($T_c \approx5 K$) and more recently Wen et al. in $A_xCoO_{2+\delta}$ ($A = Na,K$)(\tc$\approx~31 K$). We model a reference neutral \cob layer as an orbitally non-degenerate spin-\half antiferromagnetic Mott insulator on a triangular lattice and Na__x CoO_2.yH_2O and $A_xCoO_{2+\delta}$ as electron doped Mott insulators described by a t-J model. It is suggested that at optimal doping chiral spin fluctuations enhanced by the dopant dynamics leads to a d-wave superconducting state. A chiral RVB metal, a PT violating state with condensed RVB gauge fields, with a possible weak ferromagnetism and low temperature p-wave superconductivity are also suggested at higher dopings.Comment: 4 pages of LaTex file, 6 figures in eps files. Typos and minor corrections mad

Response of a spaceborne gravitational wave antenna to solar oscillations

We investigate the possibility of observing very small amplitude low frequency solar oscillations with the proposed laser interferometer space antenna (LISA). For frequencies $\nu$ below $3\times 10^{-4} {\rm Hz}$ the dominant contribution is from the near zone time dependent gravitational quadrupole moments associated with the normal modes of oscillation. For frequencies $\nu$ above $3\times 10^{-4} {\rm Hz}$ the dominant contribution is from gravitational radiation generated by the quadrupole oscillations which is larger than the Newtonian signal by a factor of the order $(2 \pi r \nu/ c)^4$, where $r$ is the distance to the Sun, and $c$ is the velocity of light. The low order solar quadrupole pressure and gravity oscillation modes have not yet been detected above the solar background by helioseismic velocity and intensity measurements. We show that for frequencies $\nu \lesssim 2\times 10^{-4} {\rm Hz}$, the signal due to solar oscillations will have a higher signal to noise ratio in a LISA type space interferometer than in helioseismology measurements. Our estimates of the amplitudes needed to give a detectable signal on a LISA type space laser interferometer imply surface velocity amplitudes on the sun of the order of 1-10 mm/sec in the frequency range $1\times 10^{-4} -5\times 10^{-4} {\rm Hz}$. If such modes exist with frequencies and amplitudes in this range they could be detected with a LISA type laser interferometer.Comment: 16 pages, 6 figures, 1 table. A reworked and considerably improved version of ArXiv:astro-ph/0103472, Published in PR

Effective action of magnetic monopole in three-dimensional electrodynamics with massless matter and gauge theories of superconductivity

We compute one-loop effective action of magnetic monopole in three-dimensional electrodynamics of massless bosons and fermions and find that it contains an infrared logarithm. So, when the number of massless matter species is sufficiently large, monopoles are suppressed and in the weak coupling limit charged particles are unconfined. This result provides some support to gauge theories of high-temperature superconductors. It also provides a mechanism by which interlayer tunneling of excitations with one unit of the ordinary electric charge can be suppressed while that of a doubly charged object is allowed.Comment: 8 pages, LATEX, UCLA/93/TEP/41 (the last sentence of the paragraph concerning applications at the end of the paper has been deleted; mailing problems have been corrected

The Principle of Valence Bond Amplitude Maximization in Cuprates: How it breeds Superconductivity, Spin and Charge Orders

A simple microscopic principle of `Valence bond (nearest neighbor singlet) amplitude maximization '(VBAM) is shown to be present in undoped and optimally doped cuprates and unify the very different orderings such as antiferromagnetism in the Mott insulator and the robust superconductivity accompanied by an enhanced charge and stripe correlations in the optimally doped cuprates. VBAM is nearly synonymous with the energy minimization principle. It is implicit in the RVB theory and thereby makes the predictions of RVB mean field theory of superconductivity qualitatively correct.Comment: 4 pages, RevTe

Gapless Fermions and Quantum Order

Using 2D quantum spin-1/2 model as a concrete example, we studied the relation between gapless fermionic excitations (spinons) and quantum orders in some spin liquid states. Using winding number, we find the projective symmetry group that characterizes the quantum order directly determines the pattern of Fermi points in the Brillouin zone. Thus quantum orders provide an origin for gapless fermionic excitations.Comment: 23 pages. LaTeX. Homepage http://dao.mit.edu/~we

Two Phases for Compact U(1) Pure Gauge Theory in Three Dimensions

We show that if actions more general than the usual simple plaquette action ($\sim F_{\mu\nu}^2$) are considered, then compact $U(1)$ {\sl pure} gauge theory in three Euclidean dimensions can have two phases. Both phases are confining phases, however in one phase the monopole condensate spontaneously `magnetizes'. For a certain range of parameters the phase transition is continuous, allowing the definition of a strong coupling continuum limit. We note that these observations have relevance to the `fictitious' gauge field theories of strongly correlated electron systems, such as those describing high-$T_c$ superconductors.Comment: 10 pages, Plain TeX, uses harvma

Magneto-optics induced by the spin chirality in itinerant ferromagnet Nd2_2Mo2_2O7_7

It is demonstrated both theoretically and experimentally that the spin chirality associated with a noncoplanar spin configuration produces a magneto-optical effect. Numerical study of the two-band Hubbard model on a triangle cluster shows that the optical Hall conductivity $\sigma_{xy}(\omega)$ is proportional to the spin chirality. The detailed comparative experiments on pyrochlore-type molybdates $R_2$Mo$_2$O$_7$ with $R=$Nd (Ising-like moments) and $R=$Gd (Heisenberg-like ones) clearly distinguishes the two mechanisms, i.e., spin chirality and spin-orbit interactions. It is concluded that for $R$=Nd, $\sigma_{xy}(\omega)$ is dominated by the spin chirality for the dc ($\omega=0$) and the $d \to d$ incoherent intraband optical transitions between Mo atoms.Comment: 4 pages, 5 figures. submitted to Phys. Rev.

Transition metal titanium (Ti) doped LaFeO3 nanoparticles for enhanced optical structural and magnetic properties

A series of LaFe1−xTixO3 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles have been successfully synthesized by simple co-precipitation technique. The synthesized samples (calcined at 800° C/3hr) were characterised for structural, optical and magnetic properties. Structural phase formation of the crystal shows orthorhombic planes of these samples phases. The average crystallite size (Dc) is decreasing with a dopant and found to be varying between ∼ 9 and 25 nm. Tailored surface morphology was analyzed using scanning electron microscope (FESEM) and transmission electron microscopes (TEM) with selected area electron diffraction pattern (SAED) also confirms the evolution of orthorhombic phases. Diffuse reflectance spectra (DRS) are recorded to evaluate the variation of optical band gap (Eg) upon titanium doping into the LaFeO3 system. The obtained results attributed that Eg values are increasing with dopant altering between 2.05 and 2.61 eV. The metal oxide (M - O) stretching vibrations and few functional groups are detected from infrared spectra (IR). The weak ferromagnetic behaviour is observed from hysteresis loop behaviour. Additionally, the large hysteresis loop behaviour induces no saturation up to 15 kOe in nanoparticles coercivity (Hc) and anisotropy constants (K1) are eventually decreasing with ‘x’ values

Novel phase diagram of superconductor NaxCoO2-yH2O in a 75 % relative humidity

We succeeded in synthesizing the powder samples of bilayer-hydrate sodium cobalt oxide superconductors NaxCoO2-yH2O with Tc = 0 ~ 4.6 K by systematically changing the keeping duration in a 75 % relative humidity atmosphere after intercalation of water molecules. From the magnetic measurements, we found that the one-day duration sample does not show any superconductivity down to 1.8 K, and that the samples kept for 2 ~ 7 days show superconductivity, in which Tc increases up to 4.6 K with increasing the duration. Tc and the superconducting volume fraction are almost invariant between 7 days and 1month duration. The 59Co NQR spectra indicate a systematic change in the local charge distribution on the CoO2 plane with change in duration.Comment: 4 pages, 5 figures, submitted to Journal of the Physical Society of Japa

HoloLens for medical imaging using post-mortem fetal micro-CT data

AIM AND OBJECTIVES: Demonstrate applicability of HoloLens technology for viewing post-mortem fetal micro-CT imaging data. Develop a pipeline focusing on the required editing of 3D segmentations for rendering in virtual reality (VR), file format and storage needs for medical holographic applications and the necessary functionality of a holographic application interface