Electronic structure parameters of Sm 1+ xBa 2− xCu 3O y solid solution of orthorhombic and tetragonal structure

Abstract

Two series of Sm 1+ x Ba 2− x Cu 3O y samples were prepared, both exhibiting a change from orthorhombic to tetragonal structure. The first is a series of solid solution of increasing Sm/Ba ratio, the second is a series of exact “123” cation stoichiometry with lowering oxygen content. Several quantities, such as electrical resistivity in magnetic field up to 8T (ϱ), Hall carrier concentration ( n H) and thermopower ( S), were measured. Despite the different chemical nature of the deviation from the initial SmBa 2Cu 3O 6.85 composition in the two series, the transport properties of the normal state change in an analogous manner. No significant differences in the Hall mobility at room temperature were revealed between 90 K superconducting and non-metallic samples; however, a wide maximum was observed for both series for samples with intermediate T c values. The critical temperature ( T c) is depressed with increasing deviation from the initial composition in both series; however, for the solid solution there is no clear 60 K plateau as for the stoichiometric series. The electronic density of states ( g( E F)) was assessed from in-field T c measurements on the basis of the GLAG theory and, independently, from analysis of S and n H values at room temperature. Both methods revealed no significant differences in the behavior of the g( E F) between the solid solution and stoichiometric series. However, the g( E F) calculated by the first method decreases fast with deviation from the initial composition, whereas the results of the second method remain nearly constant over a wide range of composition factors. The value of the g( E F) obtained for the initial SmBa 2Cu 3O 6.85 sample from the jump of the specific heat at T c based on BCS theory also agrees well with the values calculated from transport measurements.