INTRODUCTION Crystal Growth And Spin Dynamics Study Of Electron-Doped High-Tc Superconducting Cuprates Eu2-xCexCu1-yZnyO4.

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CHAPTER I INTRODUCTION

Superconductor is a material that has zero electrical resistivity when they are cooled down to sufficiently low temperatures. Most of superconductors are cuprate compounds. One of their characteristics is that conducting planes of CuO 2 are included in their crystal structures and responsible for their electronic properties. When the CuO 2 plane loses one electron because of doping, one mobile hole remains in the CuO 2 planes, leading to the formation of a hole-doped superconducting cuprate. On the other hand, when the CuO 2 plane gets an excess electron, superconductivity realizes and forms an electron-doped superconducting cuprates. Superconductor is a promising material for future applications especially for energy saving such as for superconductor cable without any energy loss of electric power transmission and high performance power storage devices. However, the mechanism describing the role of physical properties in superconductor is still far from being understood clearly. The hole-electron doping symmetry in the high-T c cuprates has been one of central interests in relation to the mechanism of the high-T c superconductivity. Phase diagrams of the hole- and electron-doped systems are very similar to each other, leading to the view of hole-electron doping symmetry. On the other hand, some properties have been found to be different each other, leading to the hole- electron doping asymmetry. From the view point of effects of nonmagnetic impurities on the Cu-spin dynamics, we have performed zero-field ZF muon-spin-relaxation SR measurements in the hole-doped cuprates La 2-x Sr x Cu 1-y Zn y O 4 Risdiana et al. , 2008, Adachi et al. , 2008 and in the electron-doped cuprates Pr 1-x LaCe x Cu 1-y Zn y O 4 Risdiana et al. , 2010, Risdiana et al. , 2005. It is found that in the hole-doped cuprates, Zn tends to induce slowing down of the Cu-spin fluctuations in the whole superconducting regime, which is able to be interpreted as being due to pinning and stabilization of the dynamically fluctuating stripes. On the other hand, in the electron-doped cuprates, the spectra are independent of the Zn concentration. That is, Zn-induced slowing down of the Cu-spin fluctuations as observed in the hole-doped system is not observed. There is no clear explanation yet for these phenomena. One of possible reasons is the effect of Pr 3+ moments on the SR spectra 2 may be stronger than that of a small amount of Zn impurities. To our knowledge, however, no one has reported the effects of magnetic impurities on the Cu-spin dynamics in the electron-doped cuprates so that clear conclusion of the relation between the dynamical stripe correlations and superconductivity in the electron-doped cuprates and the conclusion for hole-electron symmetry have not yet been obtained. Here, we proposed to prepare high quality polycrystalline samples of electron-doped high-T c superconducting cuprate Eu 2-x Ce x Cu 1-y Zn y O 4 in which effect of Zn on the Cu-spin dynamics are probably clarified. The study of Cu-spin dynamics by ZF- SR in electron- doped of Eu 2-x Ce x Cu 1-y Zn y O 4 will be the first experiments in the world to clarify the Cu- spin dynamics of electron-doped cuprates. This study will give us the important information of the mechanism of superconductivity based upon the dynamical stripe correlations in the high-T c superconducting cuprates. 3

CHAPTER II LITERATURE STUDY