Determination of parameters of a system of charge carriers in Y1–2x Ca x Pr x Ba2Cu3O y within a combined analysis of temperature dependences of thermoelectric power and Nernst–Ettingshausen coefficients

Thermopower and Nernst coefficient in the Y0.85Ca0.15Ba2−xLaxCu3Oysystem: experimental results and joint quantitative analysis

“…For all the studied samples, the mobility is about 1±0.2 cm 2 (V −1 s −1 ). Such small u values are in agreement with the ones obtained earlier for other doped YBa 2 Cu 3 O y samples [30][31][32] and can be a consequence of the conduction band narrowness that should result in high values of the electron effective mass, m * . To explain qualitatively the u constancy in the Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y system, it is necessary to take into account the revealed changes of the energy spectrum parameters, first of all, the variations of the W D and C≡W σ /W D values.…”

“…For most of the samples, there is a transition to negative Q values at low temperatures that was earlier observed for some of doped YBa 2 Cu 3 O y samples [30,42]. Thus, the temperature dependences of the Nernst coefficient in Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y samples demonstrate all the peculiarities which were earlier found to be typical for the YBa 2 Cu 3 O y system with different types of doping [30][31][32]42].…”

“…This indicates the asymmetry of the dispersion law to be slightly affected by doping. It should be noted that the earlier performed analysis of our Nernst results obtained for doped Y-based HTSC showed that in all the studied systems (including undoped samples) the kW D values, though changing in different ways with increasing level of a given doping, lie in the range from −10 and −30 meV for all the studied systems [30][31][32]. Besides, there is no correlation between the asymmetry of the DOS function (characterized in our model by the b parameter) and the dispersion law, moreover, the first one is only observed in calcium-containing samples and related to an introduction of additional states into the band.…”

“…Besides, we have earlier analyzed the specific features of the Nernst effect in case of materials with a narrow conduction band and shown that this model can be used to describe well the experimental Q(T) dependences in Y-based HTSC [29]. As a result, it becomes possible to perform a joint quantitative analysis of the experimental results on the thermopower and Nernst coefficient on the basis of the narrow-band model and to determine from this analysis the energy spectrum and charge-carrier system parameters in samples of the YBa 2 Cu 3 O y system with different types of doping [30][31][32].…”