COMMENSURATE MAGNETISM AND SUPERCONDUCTIVITY IN ELECTRON-DOPED BARIUM IRON ARSENIDE (Ba (Fe1-xCox) 2 As2) SUPERCONDUCTOR

ABSTRACTS A proper and accurate definition of the structural, magnetic, electronic phase boundaries and phase diagrams provides an extremely powerful tool to study commensurate magnetism and superconductivity in electron-doped barium iron arsenide superconductor. In this research work, the theoretical investigation of the coexistence of spin density wave and superconductivity in direct electron-doping at the Fe site with Co,(Ba (Fe1-xCox) 2 As2)has been made. We consider the interplay between superconducting (SC) and commensurate spin-density-wave (SDW) orders in iron-pnictides to answer, the questions such as what is the phase diagram of cobalt doped barium iron arsenide(Ba (Fe1-xCox) 2 As2)?, what is the graph of commensurate magnetism and superconductivity in cobalt-doped barium iron arsenide superconductor?, and etc. By developing a model Hamiltonian for the system and using diagonalized Bogoliubov transformation, We have found mathematical expressions for superconducting order parameter(Δsc) as a function of superconducting transition temperature(Tc), magnetic order parameter(∆SDW ) as a function of spin density wave transition temperature (Tsdw), and spin density wave order parameter(∆SDW ) as a function of superconducting transition temperature(Tc). The phase diagrams of superconducting transition temperature versus superconducting order parameter, spin density wave transition temperature versus spin density wave order parameter and superconducting transition temperature versus spin density wave order parameter have been plotted. By combining the two phase diagrams of spin density wave transition temperature versus spin density wave order parameter and superconducting transition temperature versus spin density wave order parameter, we have obtained a phase diagram which shows the possible coexistence of spin density wave and superconductivity in (Ba (Fe1-xCox) 2 As2). The commensurate SDW order appears below the structural transition temperature and SC coexists with SDW order in under doped region. The commensurate SDW order changes into transversely incommensurate SDW order that coexists and competes with superconductivity. The coexistence phase between SC and (in) commensurate SDW orders does exist at lower superconducting transition temperature (Tc). The commensurate SDW order appears below the structural transition temperature and SC coexists with SDW order in under doped region. Near optimal superconductivity, it has been shown that the commensurate SDW order changes into transversely incommensurate SDW order that coexists and competes with superconductivity.