Bose-glass transition of the heavy-ion irradiated La(1.85)Sr(0.15)CuO4 single crystal

Abstract

Recently the vortex system in high-T(sub c) superconductors has been attracting much attention because of its rich phase structure. The study of the phase structure of a vortex system in the heavy-ion irradiated La(1.85)Sr(0.15)CuO4 single crystal was reported. The ion created tracks worked as columnar pinning centers, resulting in a new Bose-glass phase. An unirradiated (or pre-irradiated) sample, grown by the Traveling Solvent Floating Zone (TSFZ) method, had a sharp superconducting transition at 37.5 K. One of such samples was irradiated parallel to the c-axis by the 3.4 GeV Xe ions produced from the RIKEN (Institute of Physical and Chemical Research) Ring Cyclotron. It was noted that the absolute value of the magnetization of the sample with B(sub Phi) = 0.5 T was enhanced by a factor of about 2.8 compared with the unirradiated one. The imaginary part of the AC susceptibility of the unirradiated sample showed a peak at a temperature below the critical temperature T(sub c). Above the crossover filed, the imaginary part of the susceptibility of the irradiated sample became asymmetric and had another small broad peak at a lower temperature.

最近、高T(sub c)超伝導体における渦系がその豊かな位相構造のために注目を集めている。重イオン照射したLa(1.85)Sr(0.15)CuO4単結晶における渦系の位相構造の研究について報告する。イオンにより生成されたトラックが柱状の磁気固定中心として働き、結果として新しいボーズグラス相を生じる。移動溶媒浮遊帯(TSFZ)法で成長させた非照射(或は、照射前)標本は37.5Kでシャープな超伝導転移を示す。この様な標本の1つに理化学研究所リングサイクロトロンで生成した3.4GeVのXeイオンをc軸に平行に照射した。B(sub Φ)=0.5Tでの標本の磁化の絶対値が非照射標本と比較して約2.8倍になっていることに注目した。非照射標本の AC磁化率の虚数部分は臨界温度T(sub c)以下でピークを示す。一方、照射標本の虚数部分は転座場の以上で非対称となって、低温では別の小さな幅広いピークを持つ。