Modulation of the Curie Temperature in Ferromagnetic/Ferroelectric Hybrid Double Quantum Wells

We propose a ferromagnetic/ferroelectric hybrid double quantum well structure, and present an investigation of the Curie temperature (Tc) modulation in this quantum structure. The combined effects of applied electric fields and spontaneous electric polarization are considered for a system that consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well. We calculate the change in the envelope functions of carriers at the lowest energy sub-band, resulting from applied electric fields and switching the dipole polarization. By reversing the depolarizing field, we can achieve two different ferromagnetic transition temperatures of the ferromagnetic quantum well in a fixed applied electric field. The Curie temperature strongly depends on the position of the Mn \delta-doped layer and the polarization strength of the ferroelectric well.Comment: 9 pages, 5 figures, to be published in Phys. Rev. B (2006) minor revision: One of the line types is changed in Fig.

Quantum Dynamics for de Sitter Radiation

We revisit the Hamiltonian formalism for a massive scalar field and study the particle production in a de Sitter space. In the invariant-operator picture the time-dependent annihilation and creation operators are constructed in terms of a complex solution to the classical equation of motion for the field and the Gaussian wave function for each Fourier mode is found which is an exact solution to the Schr\"odinger equation. The in-out formalism is reformulated by the annihilation and creation operators and the Gaussian wave functions. The de Sitter radiation from the in-out formalism differs from the Gibbons-Hawking radiation in the planar coordinates, and we discuss the discrepancy of the particle production by the two methodComment: LaTex 12 pages, no figure; CosPA2011, Peking Univ., Oct. 28-31, 2011; references added; to be published in International Journal of Modern Physics: Conference Serie

Light Hadron Spectrum in Quenched Lattice QCD with Staggered Quarks

Without chiral extrapolation, we achieved a realistic nucleon to (\rho)-meson mass ratio of (m_N/m_\rho = 1.23 \pm 0.04 ({\rm statistical}) \pm 0.02 ({\rm systematic})) in our quenched lattice QCD numerical calculation with staggered quarks. The systematic error is mostly from finite-volume effect and the finite-spacing effect is negligible. The flavor symmetry breaking in the pion and (\rho) meson is no longer visible. The lattice cutoff is set at 3.63 (\pm) 0.06 GeV, the spatial lattice volume is (2.59 (\pm) 0.05 fm)(^3), and bare quarks mass as low as 4.5 MeV are used. Possible quenched chiral effects in hadron mass are discussed.Comment: 5 pages and 5 figures, use revtex

Dielectric constants of Ir, Ru, Pt, and IrO2: Contributions from bound charges

We investigated the dielectric functions $\epsilon$($\omega$) of Ir, Ru, Pt, and IrO$_2$, which are commonly used as electrodes in ferroelectric thin film applications. In particular, we investigated the contributions from bound charges $\epsilon^{b}$($\omega$), since these are important scientifically as well as technologically: the $\epsilon_1^{b}$(0) of a metal electrode is one of the major factors determining the depolarization field inside a ferroelectric capacitor. To obtain $\epsilon_1^{b}$(0), we measured reflectivity spectra of sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7 meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings to extract $\epsilon_1^{b}$(0) values. Ir, Ru, Pt, and IrO$_2$ produced experimental $\epsilon_1^{b}$(0) values of 48$\pm$10, 82$\pm$10, 58$\pm$10, and 29$\pm$5, respectively, which are in good agreement with values obtained using first-principles calculations. These values are much higher than those for noble metals such as Cu, Ag, and Au because transition metals and IrO$_2$ have such strong d-d transitions below 2.0 eV. High $\epsilon_1^{b}$(0) values will reduce the depolarization field in ferroelectric capacitors, making these materials good candidates for use as electrodes in ferroelectric applications.Comment: 26 pages, 6 figures, 2 table