High Temperature Superconductivity by Shin-ichi Uchida

Author:Shin-ichi Uchida
Language: eng
Format: epub
Publisher: Springer Japan, Tokyo

Fig. 3.17 T c opt of LnBa2Cu3O7 (Ln123) for different rare-earth elements Ln in the order of increasing atomic number or decreasing radius of Ln3 + ionic state. Pr123 is not a superconductor due to a circumstance arising from the special Pr ionic state, and T c opt of La123 is relatively low because of the disorder in the BaO block due to La-Ba intersite mixing

3.6 Possibility of Enhancing T c

After the maximum value of T c = 135 K was recorded in 1993, T c has stopped rising for more than 21 years. This does not imply that we should give up the effort to obtain higher T c values. There is a possibility or hope of enhancing the cuprate T c in view of the following observations; (i) the superconducting gap magnitude is typically 40–50 meV which corresponds to the mean-field T c MF ~ 200 K or higher, (ii) the SC fluctuations or Cooper pair without phase coherence seem to exist at temperatures as high as 200 K, and (iii) T c = 164 K was actually attained by applying high pressure to the Hg1223 cuprate [12]. To the best of the current understanding, major causes of the diverse T c opt are the number of CuO2 planes n (multilayer effect), disorder in the charge reservoir blocks, and the apical oxygen position/distance. These, in turn, show the way to further increase T c.

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