Superconductivity ofPr2−xCexCu

Matthias Brinkmann

¹

,

H. Bach

²

,

K. Westerholt

³

Impurities in multiband superconductors

“…In electron-doped systems (n-type), the situation is analogous to the conventional superconductors Ð nonmagnetic impurities weakly suppress T c , while magnetic ones cause a collapse of superconductivity for an impurity concentration of about one percent, which is in close agreement with the Abrikosov±Gor'kov theory. These results follow from studies of both polycrystalline samples [42,43] and Pr 2Àx Ce x Cu 1Ày M y O 4z single crystals with M Ni, Co [44].…”

“…One of the significant differences between this expression and the analogous one for nonmagnetic impurities [see formula (44) and (45)] is the minus sign before the term originating from impurity scattering in equation (68). In the presence of interband-only scattering (Z 0), we derive here the remarkable result…”

Critical temperature of an anisotropic superconductor containing both nonmagnetic and magnetic impurities

“…This contradicts the experiments mentioned above. Besides, the experimentally observed form of the T c (ρ 0 ) curve is usually close to linear [42,44,47,52,53,55,[57][58][59], while the theory predicts a positive curvature of the T c (ρ 0 ) curve in a non-d-wave superconductor.…”

“…The comparison of experimental curves T c (ρ 0 ) with theoretical ones reveals that the observed reduction of T c by impurities and radiation defects is more gradual than predicted theoretically for d-wave superconductors [31,50,53,56,57,[59][60][61]. A critical value of ρ c 0 at which T c = 0 ranges from 200 µΩcm to 1500 µΩcm depending on the type of disorder and the kind of HTSC material [34,40,42,44,47,52,53,55,[57][58][59], while for a d-wave superconductor with T c ≈ 100 K the theory gives ρ c 0 ≈ 50 µΩcm [31,[59][60][61]. To reconcile the experimental findings with the d-wave symmetry of ∆(p) in HTSCs, a number of suggestions have been made, including the anisotropy of impurity scattering in the momentum space [62,63], an "intermediate" (between Cooper pairs and local bosons) state of paired electrons [64], a depletion of the hole density due to the oxygen vacancies in the CuO 2 planes [65], an anomalously small value of the plasma frequency [56,58], the spatial variation of the order parameter [66], etc [67].…”

Quasiparticles in strongly correlated electron systems in copper oxides

“…£ ÔËÔÕÇÏÂØ n-ÕËÒ ÓÂÊÎËÚËÇ Ä ÒÑAEÂÄÎÇÐËË T c ÒÓË ÊÂÏÇÜÇÐËË Cu РZn, Fe, Co, Ni ÄÒÑÎÐÇ ÔÑÅÎÂÔÖÇÕÔâ Ô ÕÇÑÓËÇÌ [220].´ÂÍ, AEÎâ ÐÇÏÂÅÐËÕÐÑÌ ÒÓËÏÇÔË Zn ÒÑAEÂ-ÄÎÇÐËÇ T c ÑÚÇÐß ÔÎÂÃÑÇ,  ÏÂÅÐËÕÐÞÇ ÒÓËÏÇÔË Ni Ë Co, ÔÑÅÎÂÔÐÑ AEÂÐÐÞÏ [221,222], ÒÑÎÖÚÇÐÐÞÏ Ð ÍÇÓÂÏËÚÇÔÍËØ ÑÃÓÂÊÙÂØ, ÒÑAEÂÄÎâáÕ ÔÄÇÓØÒÓÑÄÑAEËÏÑÔÕß ÒÑÎÐÑÔÕßá ÖÉÇ ÒÓË ÍÑÐÙÇÐÕÓÂÙËË $ 1 %.¯ÇAEÂÄÐËÇ ËÔÔÎÇAEÑÄÂÐËâ РÏÑÐÑÍÓËÔÕÂÎÎÂØ Pr 2Àx Ce x Cu 1Ày M y O 4z Ô M=Ni, Co ÒÑAE-ÕÄÇÓAEËÎË AEÂÐÐÞÇ AEÎâ ÍÇÓÂÏËÍ Ë ÒÑÍÂÊÂÎË, ÚÕÑ dT c a dy À20 ¬ (ÂÕ.%) À1 ÍÂÍ AEÎâ Ni, ÕÂÍ Ë AEÎâ Co [223]. ¿Õ ÔÍÑÓÑÔÕß ÒÑAEÂÄÎÇÐËâ T c ÒÓË ÊÂÏÇÜÇÐËË ÏÇAEË ÒÇÓÇ-ØÑAEÐÞÏË ÏÇÕÂÎÎÂÏË ÐÂËÃÑÎßÛÂâ AEÎâ ÄÔÇØ ËÔÔÎÇAEÑÄÂÐ-ÐÞØ ÑÍÔËAEÑÄ ÏÇAEË.…”