Superconductivity, Seebeck coefficient, and band structure transformation in Y1−x CaxBa2Cu3−x CoxOy (x=0–0.3)

TThermodynamics of the thermoelectric working fluid close to the superconducting phase transition

“…This increase was accompanied by a strong enhancement of the power factor. Broadened Seebeck coefficient peaks were found in varying pnictides compositions [30,31], as well as in cuprates [32]. In the present work, our models focus only on the thermodynamics of the ideal electronic systems, and as shown in Fig.…”

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

“…As a result, the thermopower does not demonstrate a near temperature-independent behavior at high temperatures that is typical for Y-based HTSC [2,4] including samples with a single La doping [40]. This is due to the well-known effect of calcium doping, manifested itself in calcium-containing samples with different types of its incorporation into the lattice [4,34,37,38]. Second, in the YBa 2−x La x Cu 3 O y system the thermopower at room temperature increases almost linearly with x at x=0-0.3 [4,40], while in the Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y one it remains constant at x0.1 and increases linearly with a further rise in x (see figure 4).…”

“…Note that when discussing this issue, it is more appropriate to use the C≡W σ /W D value instead of the W σ one. According to our previous results [4,14,27,28,32,37,[39][40][41], the main mechanism responsible for the band transformation under doping in different HTSC systems is the Anderson localization of states at the band edges caused by a disorder in oxygen and/or cation sublattices. The variation of the above ratio gives information on the change in this localization degree, namely, the lower the C value the stronger the state localization.…”

“…If the superconductivity was preliminary suppressed by the introduction of other impurities, doping by calcium can lead to a rise in T c [4,[33][34][35][36]. Besides, calcium-containing samples are characterized by the existence of additional peculiarities in the temperature and concentration dependences of the transport coefficients, in particular, by a linear increase in the thermopower value with decreasing temperature [4,34,37,38] that is not observed in case of other types of doping in YBa 2 Cu 3 O y . We have earlier assumed that calcium affects directly the band responsible for the conduction process due to the appearance of additional states forming a local peak in the density-of-states (DOS) function [34].…”

“…We have earlier assumed that calcium affects directly the band responsible for the conduction process due to the appearance of additional states forming a local peak in the density-of-states (DOS) function [34]. This assumption has allowed us to explain an unusual modification of the transport and superconducting properties under calcium doping in calcium-containing samples of different compositions [4,[34][35][36][37]39]. A calcium-induced peak in the DOS function in case of the studied Y 0.85 Ca 0.15 Ba 2−x La x Cu 3 O y samples with a fixed calcium content can be assumed to remain unchanged.…”