Phase diagram, cuprate superconductors

Figure 8.9 Simplified generic phase diagram for cuprate superconductors.

Figure 6.3. High Tq cuprate superconductors (HTSC) as catalysts (a) structural schematic diagram of YBa2Cu307 ( 123 ) HTSC with Cu02 sheets (b) HRTEM atomic image of the 123 phase in [010] projection with ED pattern. The image is recorded near the Scherzer defocus. The positions of the Y, Ba and Cu atom columns are indicated. The layer separation is "- 1.18 nm and the unit cell is outlined. (After Gai and Thomas 1991.)...

We have hitherto discussed cuprate superconductors with holes as charge carriers. Cuprates of T structure (Fig. 7.16) such as Nd2-jcCe Cu04 and Nd2Cu04 F are electron superconductors. There is however some symmetry in the phase diagrams of the electron and hole superconductors (Maple, 1990) as can be seen from Fig. 7.27. 

The problem of phase separation in cuprates superconductors has been longely debated [1-8], Recently, several experiments show the formation of electronic crystals at critical densities [9, 10], These results provide a strong experimental support for the scenario proposed some years ago (11-14) for the phase diagram of cuprate superconductors where generalized Wigner... 

Cuprate superconductors exhibit complicated phase diagrams which are functions of the doping parameter, x which controls the amount of the electron-transfer into or out of the cuprate plane. See for example Fig. 8.2. 

Fig. 10. Schematic phase diagram of Y123 and Y124 cuprate superconductors. In the underdoped regime, a pseudogap state forms below a temperature T > 7. The curves for 7 and 7 cross at optimal doping where the pseudogap and the superconductivity develop at the same tempeiature. T is determined from the c-axis conductivity the doping level is determined from the superfluid density = n/ni in the CUO2 planes. From Puchkov et al. (1996a).

Then, from fig.lc it is seen that SC transition onset points Tconset(H)(= Tk(H)) are at the Bloch-Gruneisen curve (dashed curve). On the other hand, such a picture is characteristic for low temperature superconductors described by s-wave BCS theory. From this analogy it may be concluded that in the cuprates the SC order parameter is of s-wave symmetry, also. Moreover, as seen from magnetic phase H-T diagram, the... 

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