M. Aoyama

Cu-site-substitution effects on the 1/8 anomaly in the high-Tc cuprates and on the anomaly at x=0.21 in La2−xSrxCuO4

Effects of the Cu-site substitution on the 1/8 anomaly in the Bi-2212 and Y-123 phases and also on the anomaly at x = 0.21 in La 2-x Sr x CuO 4 (LSCO) have been investigated from the transport, muon-spin relaxation and neutron-scattering measurements. It is suggested that the dynamical stripe correlations of spins and holes exist in the Bi-2212 and Y-123 phases as well as in the La-214 phase and that they tend to be pinned by Zn at the hole concentration of ∼1/8 per Cu in the high-T c cuprates and also at x = 0.21 in LSCO. Based upon the stripe-pinning model, universal properties in the high-T c cuprates that partially substituted Zn is a strong scatterer and that the Zn substitution markedly suppresses the superconductivity are also discussed.

POSSIBLE CHARGE AND/OR SPIN ORDERING IN THE Bi-2212, Y-123 AND La-214 PHASES

Our recent experimental studies on the so-called 1/8 anomaly in the Bi-2212 and Y-123 phases and also on the new anomaly in the overdoped region of the La-214 phase are reviewed. In the partially Zn-substituted Bi-2212 and Y-123 phases, we have found anomalous suppression of superconductivity (SC) at p (the hole concentration per Cu in the CuO2 plane) ~1/8, and it has been found from the muon-spin-relaxation (μSR) measurements that the magnetic correlation between Cu spins is enhanced singularly at p~1/8. Furthermore, we have found giant suppression of SC singularly at x=0.21 in the 1% Zn-substituted single-crystals of La2-xSrxCu1-yZnyO4 (LSCZO), and it has been found from the μSR measurements that the magnetic correlation is also enhanced at x=0.21. These results suggest that the dynamical stripe correlations of holes and spins exist in the Bi-2212 and Y-123 phases as well as in the La-214 phase and that they tend to be pinned by a small amount of Zn, leading to quasi-static stripe order and the suppress...

Possible stripe ordering at x = 0.21 in La2-xSrxCu1-yZnyO4

Abstract Anomalies, which we have recently discovered at x =0.21 in La 2− x Sr x Cu 1− y Zn y O 4 single crystals, are reviewed. In the 1% Zn-substituted crystal with x =0.21, the resistivity exhibits an upturn at low temperatures below about 80 K and the superconductivity (SC) is markedly suppressed. The muon-spin-relaxation ( μ SR) measurements have revealed the existence of a static ordered state of Cu spins in this crystal at low temperatures below 2 K. From the elastic neutron-scattering experiment, incommensurate magnetic peaks around ( π , π ) have been observed in this crystal at low temperatures below 20 K. Even in the Zn-free crystal with x =0.21, the SC is a little suppressed and the magnetic correlation has been found from the μ SR measurements to be enhanced at low temperatures below about 0.8 K. These results strongly suggest that the dynamical stripe correlations of spins and holes tend to become static singularly at x =0.21 and are pinned by a small amount of Zn at x =0.21, leading to the static stripe-order and the marked suppression of SC, as in the case of x =0.115.

Impurity effects on the stripes in the La-214, Bi-2212 and Y-123 phases

Our recent experimental studies on the 1/8 anomaly in the Bi-2212 and Y-123 phases and on the new anomaly at x=0.21 in La2−xSrxCu1−yZnyO4 are reviewed. In the Zn-substituted Bi-2212 and Y-123 phases, we have found anomalous suppression of superconductivity at p (the hole concentration per Cu in the CuO2 plane) ∼1/8, and it has been found from the muon spin relaxation (μ SR) measurements that the magnetic correlation between Cu spins is enhanced singularly at p∼1/8. Furthermore, we have found marked suppression of superconductivity singularly at x=0.21 in the 1% Zn-substituted single-crystals of La2−xSrxCu1−yZnyO4, and it has been found from the μ SR measurements that the magnetic correlation is also enhanced at x=0.21. These results suggest that the dynamical stripe correlations of holes and spins exist in the Bi-2212 and Y-123 phases as well as in the La-214 phase and that they tend to be pinned by Zn, leading to the suppression of superconductivity. If this tendency is the case in a wide range of p, it ...

μ+SR study on hole-doped high-Tc oxides around the hole concentration of per Cu

Abstract Muon spin relaxation (μSR) measurements were applied to the Zn-substituted YBCO system, YBa2Cu3−2yZn2yO7−δ, around the hole concentration p= 1 8 per Cu in the CuO2 plane, and to the Ga-substituted LSCO system, La2−xSrxCu1−yGayO4 in the overdoped region. Enhancement of the muon-spin-depolarization rate was observed at low temperatures in both systems, indicating the enhancement of the magnetic correlation between Cu spins. Our μSR results on the Zn-substituted YBCO system suggest the existence of the so-called 1 8 -effect also in the YBCO system. The results on the Ga-substituted LSCO system in the overdoped region are suggestive of the existence of a kind of a spin ordered state.

μSR STUDY ON THE Cu-SPIN STATE IN La2-xSrxCu1-yZnyO4

Static and dynamical properties of Cu spins in the overdoped single-crystals of La2-xSrxCu1-yZnyO4 have been investigated by the muon-spin-relaxation (μSR) method. In the Zn-substituted single-crystal with x=0.21 and y=0.01, where the high-Tc superconductivity is anomalously suppressed, a coexisting state of statically ordered Cu-spins and localized holes has been found at low temperatures below about 2 K. The dynamical depolarization rate of the muon spin at 3.0 K has been found to be nearly proportional to minus-root-square of the external magnetic-field applied along the initial muon-spin polarization. This field-dependence can be explained by assuming the existence of an excited state of the Cu spins diffusing in a one-dimensional direction. The present study suggests a high possibility of the existence of a new one-dimensional stripe ordered state of the Cu spins and doped holes at x=0.21 in the overdoped region of La2-xSrxCu1-yZnyO4.

Transport and Tc Anomalies around x=0.22 in La2−xSrxCu1−yM y O4 (M=Zn, Ga, Ni): Possibility of Charge and/or Spin Ordering

Transport and Tcanomalies around x=0.22 in La2−xSrxCuO4have been studied through the partial substitution of Zn, Ga and Ni for Cu. It has been found that the value of x where the anomalies occur shifts to lower x values through the Zn substitution, while it shifts to larger x values through the Ga substitution, and it disappears through the Ni substitution. There is a possibility that an order of holes and/or spins, such as the so-called stripe order, is formed or fluctuates around x=0.22 in La2−xSrxCuO4.

Transport and Tc Anomalies around x=0.22 in La2−xSrxCu1−yMyO4 (M=Zn, Ga, Ni): Possibility of Charge and/or Spin Ordering

Transport and Tcanomalies around x=0.22 in La2−xSrxCuO4have been studied through the partial substitution of Zn, Ga and Ni for Cu. It has been found that the value of x where the anomalies occur shifts to lower x values through the Zn substitution, while it shifts to larger x values through the Ga substitution, and it disappears through the Ni substitution. There is a possibility that an order of holes and/or spins, such as the so-called stripe order, is formed or fluctuates around x=0.22 in La2−xSrxCuO4.