两带超导体LaNiC_2上临界磁场的理论分析  

Theoretical analysis of the upper critical field of two-band superconductor LaNiC_2

作　　者：刘敏霞[1] 何林[1] 张耿[1] 叶海[1] 黄晓园[1] 徐永钊[1] 

机构地区：[1]东莞理工学院电子工程学院,东莞523808

出　　处：《物理学报》2016年第3期279-283,共5页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:61501118);广东省自然科学基金(批准号:2014A030310262);广东省高等学校优秀青年教师培养计划资助的课题~~

摘　　要：非中心对称超导体LaNiC_2是传统BCS超导体还是能隙存在节点又或是两带超导体,目前仍然存在争议.基于此,文章用两带Ginzburg-Landau理论分析了超导体LaNiC_2的上临界磁场随温度的变化关系,计算结果与实验结果在整个温度区间内符合得很好,说明LaNiC_2是两带超导体,和陈健等人的观点一致.文章还分析了两个不同能带对上临界磁场的影响,发现相对较小的相干长度对LaNiC_2的上临界磁场影响较大.LaNiC2 is one of ternary RNiC2 compounds,where R is a rare earth or Y.Its space group is Amm2.the symmetry along the c-axis of the crystal structure lacks inversion symmetry along the c-axis.In 2009,Hillier et al.performed the muon spin relaxation experiment（SR）which implied that time-reversal symmetry is broken in LaNiC2.As a weak correlation noncentrosymmetric superconductor,LaNiC2 has attracted wide research interest in recent years.Though a lot of theoretical and experimental studies have been carried out,the order parameter of this compound remains highly controversial.The measurements of specific heat and nuclear quadrupole relaxation suggest that LaNiC2 is ＂normally BCS-like＂,which is further supported by theoretical calculations.But recently another study showed that the London penetration depth depends on T2 below 0.4 Tc indicative of nodes in the energy gap.Evidence of possible nodal superconductivity can also be inferred from the early measurements of specific heat given by Lee et al.However,the experimental results obtained by Chen et al.supported the existence of two-gap superconductivity in LaNiC2.Based on the above case,the two-band Ginzburg-Landau theory is used to study the temperature dependence of the upper critical field for the superconductor LaNiC2 in this paper.Choosing the Ginzburg-Landau theory for calculating the upper critical field is just because Ginzburg-Landau theoretical model is simple,easy to understand,low-calculation,and the clear physical meanings of the parameters.The theoretical results in this paper accord with the experimental data very well in the whole temperature range.The curve of H（c2）（T） has an obvious positive curvature near the critical temperature,which is typical feature of multi-gap superconductor.Therefore,our results show strong evidence that two-gap scenario is better to account for the superconductivity of LaNiC2,consistent with the results of Chen Jian et al.The influences of two different energy bands on the upper critical field are also st

关 键 词：两带超导体 Ginzburg-Landau理论 上临界磁场 LaNiC2 

分 类 号：O511.3[一般工业技术—材料科学与工程]