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

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Abstract

Anomalies, which we have recently discovered at x=0.21 in La2−xSrxCu1−yZnyO4 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 (μSR) 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 μSR 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.

Introduction

A few years ago, it has been pointed out from the inelastic neutron-scattering experiments that dynamical stripe correlations of spins and holes exist in a wide range of hole concentration in the La-based cuprate, where the high-Tc superconductivity (SC) appears [1]. Therefore, the dynamical stripe correlations have attracted great interest in relation to the mechanism of the high-Tc SC. However, when the dynamical stripe correlations are pinned by the tetragonal low-temperature structure or Zn to become a static or quasi-static stripe-order at p (the hole concentration per Cu) ∼1/8, the SC is markedly suppressed [2], [3]. This is called 1/8 anomaly, which may be understood to be due to the good matching between the stripe structure and the crystal lattice in the CuO2 plane. In order to confirm the existence of the dynamical stripe correlations in a wide range of p, we searched for another anomaly around p=1/4 in the overdoped region of La2−xSrxCu1−yZnyO4 polycrystalline samples, because a similar static stripe-order had been observed at various values of the hole concentration of 1/2, 1/3, 1/4 per Ni in La2NiO4+δ or La2−xSrxNiO4 [4]. Here, Zn was introduced into the samples to pin the dynamical stripe correlations effectively. Consequently, we found a little anomaly at x=0.19−0.23 in La2−xSrxCu1−yZnyO4 polycrystalline samples [5], [6]. Moreover, recently, we have discovered marked suppression of SC at x=0.21, using single crystals of good quality [7].

In this paper, we review our experimental studies by the electrical resistivity, magnetic susceptibility, muon-spin-relaxation (μSR) [8] and elastic neutron-scattering [9] around x=0.21 in La2−xSrxCu1−yZnyO4 single crystals, which suggest the pinning of the dynamical stripe correlations at x=0.21.

Section snippets

Experimental

Single crystals of La2−xSrxCu1−yZnyO4 with y=0 and 0.01 were grown by the TSFZ method. The ICP analysis revealed that the Sr content x in each crystal was almost the same as the nominal value within the accuracy of ±0.01 and that the Zn content y in each crystal with nominally y=0.01 was 0.008±0.002. Electrical-resistivity measurements were carried out by the dc four-point probe method. The magnetic susceptibility was measured using a SQUID magnetometer, to determine the superconducting

Results and discussion

Fig. 1 shows the temperature dependence of the electrical resistivity ρab in the ab plane and ρc along the c-axis for the 1% Zn-substituted crystals [7]. It is found that the resistivity exhibits upturn at low temperatures below about 80 K at x=0.21 in both ρab and ρc, while no upturn is observed for the Zn-free crystals in the overdoped region of x⩾0.19. This means that carriers are localized more or less at low temperatures at x=0.21 in the 1% Zn-substituted crystals.

Fig. 2 displays the x

Summary

We have discovered several anomalies at x=0.21 in La2−xSrxCu1−yZnyO4 single crystals. In the 1% Zn-substituted crystal with x=0.21, the resistivity exhibits upturn at low temperatures below about 80 K and the SC is markedly suppressed. The μSR 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

Acknowledgements

This work was supported by a Grant-in-aid for Scientific Research from the Ministry of Education, Science, Sports and Culture, Japan, and also by CREST of Japan Science and Technology Corporation.

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    Citation Excerpt :

    At high doping, not only at x=1/8 but also at x=1/5 static stripe ordering might be promoted. Koike et al. (2001) report resistivity, neutron scattering and μSR data for La2−xSrxCu1−yZnyO4 with y=0.01. At 2 K dynamical stripe correlations of spins and holes seem to become static.

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