Superconducting and transport properties of TmBa 2Cu 3O 7− δ and comparison to YBa 2Cu 3O 7− δ

Abstract

TmBa 2Cu 3O 7− δ ceramic samples with oxygen contents between ∼6.7 and 7 have been characterized in terms of their superconducting transition temperatures ( T c), temperature dependencies of resistivity ( ρ( T)), thermopowers ( S( T)) and Hall coefficients ( R H( T)) and specific heat jumps at T c (Δ C p ). The behaviors of these parameters are compared with those exhibited by YBa 2Cu 3O 7− δ samples. In general, the temperature dependencies of ρ, S and R H found for TmBCO are similar to those for YBCO. However, some clear quantitative differences between the compounds have been observed for the oxygen content dependencies of T c, S and Δ C p / T c, especially at low oxygen contents. TmBCO samples with oxygen contents 7− δ=6.7–6.8 show significantly lower T c and Δ C p / T c, and higher S compared toYBCO, although the carrier concentration n H at 7− δ≈6.7 is similar for both compounds (4–5×10 21 cm −3). The observed difference in the values of T c, Δ C p / T c and S seem to be caused by the large mass and magnetic moment of Tm. Thermopower, S, and carrier concentration, n H, characterize the electronic structure of the compounds. The dependence of S on 1/ n H for TmBCO and YBCO is similar and nearly linear, in agreement with the Mott relation.