The Nernst–Ettingshausen Coefficient in the Normal Phase of Doped HTSCs of the YBa[sub 2]Cu[sub 3]O[sub y] System

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

“…As the temperature decreases, the Q value for all the studied samples increases slightly, then the Q(T) dependence demonstrates a broad maximum followed by a sharp fall of the Q value. 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].…”

“…The Nernst coefficient is positive at T=300 K and its values are extremely small (they do not exceed 2.4 nV (K −1 T −1 ), see figure 4). Note that, contrary to the thermopower, the Q (T=300 K) value does not show any systematic variation with increasing doping level so that a correlation between the changes in the S(T=300 K) and Q(T=300 K) values found earlier for doped YBa 2 Cu 3 O y samples [30] is not observed in case of the Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y system. As the temperature decreases, the Q value for all the studied samples increases slightly, then the Q(T) dependence demonstrates a broad maximum followed by a sharp fall of the Q value.…”

“…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.…”

“…The Nernst coefficient was measured in a constant magnetic field of 1.8 T. We used thin samples of about 1 mm in the ∇T direction to increase the Nernst signal and a reversible magnetic field to exclude a contribution of even magnetic effects to the measured Nernst voltage. The details of the Nernst coefficient measurements can be found elsewhere [30]. The resistivity and thermopower were measured in the temperature range T=T c -300 K, the Nernst coefficient was measured at T=100-350 K. The absolute error in determination of the Nernst coefficient values when measuring the Q(T) dependences did not exceed 10%.…”

“…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].…”