Na content dependence of superconductivity and the spin correlations in NaxCoO2·1.3H2O
Na content dependence of superconductivity and the spin correlations in NaxCoO2·1.3H2O
复制标题
DOI：
10.1088/0953-8984/18/5/l02
复制
发表时间：
2006-01
期刊：
影响因子：
--
通讯作者：
G. Zheng;K. Matano;R. Meng;J. Cmaidalka;C. Chu;C. Chu;C. Chu
中科院分区：
文献类型：
--
作者：
G. Zheng;K. Matano;R. Meng;J. Cmaidalka;C. Chu;C. Chu;C. Chu
本文报道了用~（59）Co核四极共振（NQR）技术对钴氧化物超导体NaxCoO_2·1.3H_2O在较宽的Na含量范围（x = 0.25-0.34）的系统测量。我们发现，Tc随x的减小而增加，但当x≤0.28时达到一个平台。在x ≥ 0.26的样品中，自旋-晶格弛豫速率1/T1显示出低于Tc且低至T ≥ Tc/6的T3变化，这明确地表明超导（SC）能隙函数中存在线节点。然而，对于更大或更小的x，1/T1偏离T3的变化低于T102 K，即使Tc（104.7 K）是相似的，这表明一个不寻常的SC状态的演变。在正常态下，有限波矢处的自旋关联随x的减小而增强，费米能级处的态密度随x的减小而增大，这可以用LDA计算提出的单轨道图像来理解。
We report systematic measurements using the 59Co nuclear quadrupole resonance (NQR) technique on the cobalt oxide superconductors NaxCoO2·1.3H2O over a wide Na content range x = 0.25–0.34. We find that Tc increases with decreasing x but reaches a plateau for x≤0.28. In the sample with x∼0.26, the spin–lattice relaxation rate 1/T1 shows a T3 variation below Tc and down to T∼Tc/6, which unambiguously indicates the presence of line nodes in the superconducting (SC) gap function. However, for larger or smaller x,1/T1 deviates from the T3 variation below T∼2 K even though the Tc (∼4.7 K) is similar, which suggests an unusual evolution of the SC state. In the normal state, the spin correlations at a finite wavevector become stronger upon decreasing x, and the density of states at the Fermi level increases with decreasing x, which can be understood in terms of a single-orbital picture suggested on the basis of LDA calculation.