Technical Report of ISSP Ser. A: Number 2822

Abstract

Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) studies have focused on YBa2Cu3O(6+x) in order to investigate the relationship between superconductivity and antiferromagnetic fluctuations in the CuO2 plane of high-T(sub c) materials. The planar-oxygen Knight shift K-17 and nuclear spin-lattice relaxation rate ((17)T(sub 1))(exp - 1) have been determined in the superconductor YBa2Cu4O8. The present oxygen results have been analysed in connection with the planar-copper relaxation rate ((63)T(sub 1))(exp - 1) data. In the normal state, both K-17 and ((17)T(sub 1)T)(exp - 1) decrease as the temperature is lowered towards T(sub c) = 81 K, while ((63)T(sub 1)T)(exp - 1) shows a maximum around 160 K. Comparison with YBa2Cu3O(6+x) data strongly suggests that both the q and the temperature dependences of the magnetic fluctuations in YBa2Cu4O8 present a similarity to those for the 60 K phase of YBa2Cu3O(6+x) in the normal state above 110 K. In the superconducting state, ((63)-T(sub 1)T)(exp - 1) decreases drastically with decreasing temperature, while the slope for ((17)-T(sub 1)T)(exp - 1) shows a slight change near T(sub c). The considerable decrease in (17)T(sub 1)/(63)T(sub 1) below T(sub c) suggests that the loss of antiferromagnetic fluctuations is dominant in the superconducting state.

プレーナー酸素のナイト・シフト(17)Kと核スピン-格子緩和速度((17)T1)｛-1｝を超伝導体YBa2Cu4O8について求めた。酸素についての結果をプレーナー-銅緩和速度((63)T1)｛-1｝データと結びつけて解析した。通常の状態で、温度がTc=81Kより下降するにつれて(17)Kと((17)T1T)｛-1｝はともに減少し、一方((63)T1T)｛-1｝は160K付近で最高値を示した。YBa2Cu3O(6+x)データとの比較は、YBa2Cu4O8における磁気ゆらぎのqおよび温度に対する依存性が、110Kを超えた通常の状態におけるYBa2Cu3O(6+x)の60K相に対するこれら依存性と良く似ていることを強く示唆している。超伝導状態において、((63)T1T)｛-1｝は温度の下降とともに減少し、一方((17)T1T)｛-1｝に対するスロープはTcの近くでわずかの変化を示した。Tc以下での(17)T1/(63)T1におけるかなりの減少は、反強磁性ゆらぎの損失が超伝導状態において支配的であることを示唆している。