Mode conversion in periodically disturbed thin‐film waveguides

Mode conversion in a periodically perturbed thin‐film optical waveguide is studied in detail. Three different types of perturbations are considered: periodic index of refraction of the film, periodic index of refraction of the substrate, and periodic boundary. The applications in filters, mode converters, and distributed feedback lasers are discussed

Distribution networks and electrically controllable couplers for integrated optics

The power distribution as a function of propagation distance in a network of coupled optical waveguides is determined for several interesting cases. An electrically controllable coupler is proposed and analyzed in detail. High efficiency coupling and decoupling between two optical guides can be accomplished with the use of an electrooptically generated dynamic channel, of finite length, located in between the two guides

Periodic structures in integrated optics

Thin‐film dielectric waveguides with a periodic refractive index, a periodic substrate, or periodic surface are studied. The field is determined from Maxwell's equations using Floquet's theorem. The Brillouin diagram and the interaction regions are investigated. The bandwidth and the attenuation coefficients of the interaction regions are given as a function of the optical wavelength. A number of applications in active and passive integrated optics systems are discussed

The science and technology of condensed matter physics - from atomic imaging to space research

Various areas of our ongoing condensed matter physics research which involve both fundamental physics and advanced technology are described. The research topics include studies of the vortex dynamics and pairing symmetry of high-temperature superconductors; development of precision clocks using high-Q superconducting microwave cavities; state-of-the-art measurements of the density and critical phenomena of liquid helium near phase transitions and under microgravity; as well as the physics and device applications of various magnetoresistive perovskites. The experimental scope encompasses techniques from atomic imaging to space research, and the important interplay of fundamental science and frontier technology in our research is also addressed

Recent Advances in High-Temperature Superconductivity

Recent experimental and theoretical developments in high-temperature superconductivity are reviewed, and the empirically asymmetric behavior between hole-doped and electron-doped cuprates is contrasted. A number of phenomena previously considered as essential for the formation of cuprate superconductivity, such as the pairing symmetry, pseudogap phenomenon, gapped incommensurate spin fluctuations and charged stripes, are found to be non-universal, and are likely the consequence of competing orders. It is suggested that the only ubiquitous properties among all cuprates are the strong electronic correlation and antiferromagnetic spin interaction in the CuO2 planes.Comment: 24 pages, 17 figures, 166 references. Review article, to appear in the Bulletin of Associations of Asia Pacific Physical Societies (AAPPS), Vol. 12. Contact author: Nai-Chang Yeh (e-mail: [email protected]

Non-universal pairing symmetry and pseudogap phenomena in hole- and electron-doped cuprate superconductors

Experimental studies of the pairing state of cuprate superconductors reveal asymmetric behaviors of the hole-doped (p-type) and electron-doped (n-type) cuprates. The pairing symmetry, pseudogap phenomenon, low-energy spin excitations and the spatial homogeneity of the superconducting order parameter appear to be non-universal among the cuprates, which may be attributed to competing orders. We propose that the non-universal pseudogap and nano-scale variations in the quasiparticle spectra may be the result of a charge nematic (CN) phase stabilized by disorder in highly two-dimensional (2D) p-type cuprates. The CN phase is accompanied by gapped spin excitations and competes with superconductivity (SC). In contrast, gapless spin excitations may be responsible for the absence of pseudogap and the presence of excess sub-gap spectral weight in the momentum-independent quasiparticle spectra of n-type cuprates. The physical implications and further verifications for these conjectures are discussed

Kinetic Study of Electrically Activated Reacting Systems at Relatively Low Temperature Levels Progress Report, Sep. 1965 - Mar. 1966

Chemical process for study of thermodynamic and kinetic behavior of electrically activated reaction

Microstructure of hot-pressed Al2O3-Si3N4 mixtures as a function of holding temperature

Powder mixtures of 40 m/o Si3N4-60 m/o Al2O3 were hot-pressed at 4000 psi at various holding temperatures from 1100 C to 1700 C. Scanning Electron Microscopy and Transmission Electro Microscopy results were correlated to X-ray phase analysis and density measurements. The progressively developed microstructure was used to interpret the densification behavior of SiAlON. Photomicrographs of microstructures are shown

Effects of pressure and temperature on hot pressing a sialon

Mixed powders (60 m/o Al2O3-40 m/o Si3N4) were hot pressed at temperatures and pressures from 1360 to 1750 C and 3.5 to 27.5 MPa (0.5 to 4.0 ksi). Fully dense sialon bodies are obtainable at temperatures and pressures as low as 1550 C and 0.5 ksi. The fully dense bodies contain Beta prime and x-phase. There is some evidence that plastic deformation has contributed to densification

Collective modes and quasiparticle interference on the local density of states of cuprate superconductors

The energy, momentum, and temperature dependence of the quasiparticle local density of states (LDOS) of a two-dimensional d(x2)-(y2)-wave superconductor with random disorder is investigated using the first-order T-matrix approximation. The results suggest that collective modes such as spin-charge-density waves are relevant low-energy excitations of the cuprates that contribute to the observed LDOS modulations in recent scanning tunneling microscopy studies of Bi2Sr2CaCu2Ox