Browsing by Author "Dinegde, Urga"

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    Electron-Positron pair Production in Collision of Virtual Photons and pair Conversion of Virtual Bremsstrahlung Photon
    (Addis Ababa University, 2007-03) Dinegde, Urga; Bhatnagar, Shashank (PhD)
    This thesis deals with the physics of two photon processes. We first introduce covariant perturbation theory and apply it to some quantum electrodynamics processes. We start with study of electron-positron pair production in the field of a static nucleus. We then deal with applications to electron-positron pair production through collision of virtual photons in high energy electron-electron scattering. Next we study the pair conversion of bremsstrahlung photon in high energy proton-proton scattering. Detailed evaluations of cross sections are given
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    Study of Competing Charge, Spin and Superconducting Orders In Underdoped High-Temperature Superconductors.
    (Addis Ababa University, 2018-03-02) Dinegde, Urga
    Superconductivity often emerges in the proximity of, or in competition with, symmetry-breaking ground states such as antiferromagnetism or charge den- sity waves(CDW). A number of materials in the cuprate family, which includes the high transition-temperature(high-Tc) superconductors, show spin and charge density wave order. Thus a fundamental question is to what extent do these or- dered states exist for compositions close to optimal for superconductivity. Recent observations of CDWorder in Y Ba2Cu3Oy and other cuprate families have raised interesting questions regarding the general role of charge modulations and the relation to superconductivity. It was studied that in the system La2􀀀xBaxCuO4 SDW and CDW orders appear to be intertwined with a spatially-modulated superconductivity. Here by developing a model Hamiltonian and by using quan- tum _eld theory Green's function formalism, we obtain mathematical expres- sions for superconductivity order parameter(_), and charge density wave order parameter(W) in under-doped Y Ba2Cu3Oy. We plot the phase diagram of su- perconducting order parameter (_) against temperature(T) for di_erent values of charge density wave orders(W) in under-doped Y Ba2Cu3Oy. The relation- ship between superconductivity(_), charge density wave(W), and spin density wave(M) orders and their critical temperatures is studied theoretically for the under-doped La2􀀀xBaxCuO4 superconductor and plot the phase diagrams of su- perconducting order parameter(_) against temperature(T) for di_erent values of charge density wave(W) and spin density wave(M) orders. Finally, we examine the physics of combined mechanisms for cuprates and pnictides.