Study of gossamer superconductivity and antiferromagnetism in the t-J-U model

The d-wave superconductivity (dSC) and antiferromagnetism are analytically studied in a renormalized mean field theory for a two dimensional t-J model plus an on-site repulsive Hubbard interaction $U$. The purpose of introducing the $U$ term is to partially impose the no double occupancy constraint by employing the Gutzwiller approximation. The phase diagrams as functions of doping $\delta$ and $U$ are studied. Using the standard value of $t/J=3.0$ and in the large $U$ limit, we show that the antiferromagnetic (AF) order emerges and coexists with the dSC in the underdoped region below the doping $\delta\sim0.1$. The dSC order parameter increases from zero as the doping increases and reaches a maximum near the optimal doping $\delta\sim0.15$. In the small $U$ limit, only the dSC order survives while the AF order disappears. As $U$ increased to a critical value, the AF order shows up and coexists with the dSC in the underdoped regime. At half filing, the system is in the dSC state for small $U$ and becomes an AF insulator for large $U$. Within the present mean field approach, We show that the ground state energy of the coexistent state is always lower than that of the pure dSC state.Comment: 7 pages, 8 figure

Competition of Superconductivity and Antiferromagnetism in a d-Wave Vortex Lattice

The d-wave vortex lattice state is studied within the framework of Bogoliubov-de Gennes (BdG) mean field theory. We allow antiferromagnetic (AFM) order to develop self-consistently along with d-wave singlet superconducting (dSC) order in response to an external magnetic field that generates vortices. The resulting AFM order has strong peaks at the vortex centers, and changes sign, creating domain walls along lines where $\nabla \times j_s \approx 0$. The length scale for decay of this AFM order is found to be much larger than the bare d-wave coherence length, $\xi$. Coexistence of dSC and AFM order in this system is shown to induce $\pi$-triplet superconducting order. Competition between different orders is found to suppress the local density of states at the vortex center and comparison to recent experimental findings is discussed.Comment: 10 pages, 7 figure

On the dipole straylight contamination in spinning space missions dedicated to CMB anisotropy

We present an analysis of the dipole straylight contamination (DSC) for spinning space-missions designed to measure CMB anisotropies. Although this work is mainly devoted to the {\sc Planck} project, it is relatively general and allows to focus on the most relevant DSC implications. We first study a simple analytical model for the DSC in which the pointing direction of the main spillover can be assumed parallel or not to the spacecraft spin axis direction and compute the time ordered data and map. The map is then analysed paying particular attention to the DSC of the low multipole coefficients of the map. Through dedicated numerical simulations we verify the analytical results and extend the analysis to higher multipoles and to more complex (and realistic) cases by relaxing some of the simple assumptions adopted in the analytical approach. We find that the systematic effect averages out in an even number of surveys, except for a contamination of the dipole itself that survives when spin axis and spillover directions are not parallel and for a contamination of the other multipoles in the case of complex scanning strategies. In particular, the observed quadrupole can be affected by the DSC in an odd number of surveys or in the presence of survey uncompleteness or over-completeness. Various aspects relevant in CMB space projects (such as implications for calibration, impact on polarization measurements, accuracy requirement in the far beam knowledge for data analysis applications, scanning strategy dependence) are discussed.Comment: 21 pages, 13 Figures, 1 Table. To appear in MNRAS. Accepted 2006 July 13. Received 2006 July 13; in original form 2006 June 7. This work has been done in the framework of the Planck LFI activitie

The effect of silicon on the glass forming ability of the Cu47Ti34Zr11Ni8 bulk metallic glass forming alloy during processing of composites

Composites of the Cu47Ti34Zr11Ni8 bulk metallic glass, reinforced with up to 30 vol % SiC particles are synthesized and characterized. Results based on x-ray diffraction, optical microscopy, scanning Auger microscopy, and differential scanning calorimetry (DSC) are presented. During processing of the composites, a TiC layer forms around the SiC particles and Si diffuses into the Cu47Ti34Zr11Ni8 matrix stabilizing the supercooled liquid against crystallization. The small Si addition between 0.5 and 1 at. % increases the attainable maximum thickness of glassy ingots from 4 mm for Cu–Ti–Zr–Ni alloys to 7 mm for Cu–Ti–Zr–Ni–Si alloys. DSC analyses show that neither the thermodynamics nor the kinetics of the alloy are affected significantly by the Si addition. This suggests that Si enhances the glass forming ability by chemically passivating impurities such as oxygen and carbon that cause heterogeneous nucleation in the melt