1/8 PROBLEMS IN THE La-, Bi- AND Y-BASED CUPRATES AND NEW ANOMALIES IN THE OVERDOPED REGION OF THE La-BASED CUPRATE

Abstract

Recent experimental work on the 1/8 problem by our group is reviewed not only in the La-based cuprate but also in the Bi-and Y-based ones. In the partially Zn-substituted Bi2Sr2Cai_ a: Ya:(Cui_ 2/ Zn 2/ )208+5, we have found anomalous suppression of superconductivity at x = 0.30 -0.35, where the hole concentration per Cu p ~ 1/8. Moreover, it has been revealed from the //SR measurements that the Cu-spin fluctuations exhibit slowing-down behavior at low temperatures in these samples. These results are suggestive of the stripe correlations of holes and spins tending to be pinned by Zn at p ~ 1/8 in the Bi-based cuprate as well as in the La-based cuprate. In Yi_ a3 Caa;Ba2Cu307_ < $, the 60 K plateau of T c has been found not to be correlated with the oxygen content but to be interpreted as being due to the suppression of superconductivity at p ~ 1/8. Accordingly, we conclude that the 1/8 problem is common to all high-T c cuprates with the CuC>2 plane. Moreover, we have found transport and T c anomalies around x = 0.22 in La2-a;Sr a ;Cui_ 2/ M z/ 04 (M = Zn, Ga), suggesting a possibility that an order of holes and/or spins is formed or fluctuates in these samples in the overdoped region.

Changes in the Structural Parameters and Effective Magnetic Moment of Eu2−xCexCuO4+α−δ by Zn Substitution

“…As for the electron-doped system, the superconductor is formed when a part of Eu, Nd, Pr, or Sm is doped by Ce 4+ to form a superconductor (Eu,Nd,Pr,Sm) 2−-x Ce x CuO 4 with maximum T c ∼24 K [3,4]. Many studies such as structure, electrical, and magnetic properties, both in experiments, and theories have been carried out in hole-doped systems [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. However, research on electrondoped systems is still limited [22][23][24][25][26][27].…”