Dinegde, Urga2019-05-222023-11-092019-05-222023-11-092018-03-02http://10.90.10.223:4000/handle/123456789/18285Superconductivity 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.enStudy of Competing ChargeHigh-Temperature SuperconductorsSuperconducting StateZero ResistanceThesis