Pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3:: An 115In-NQR study under pressure
Pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3:: An 115In-NQR study under pressure
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DOI：
10.1103/physrevb.77.064508
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发表时间：
2008-02-01
影响因子：
3.7
通讯作者：
Onuki, Y.
中科院分区：
文献类型：
--
作者：
Kawasaki, S.;Yashima, M.;Onuki, Y.
利用核四极共振（NQR）方法研究了高压下重费米子反铁磁体CeIn 3的压力诱导非常规超导性。In-NQR谱的温度（T）和压力（P）依赖性揭示了在临界压力P-c= 2.46GPa时从反铁磁性（AFM）到顺磁性（PM）的一级量子相变（QPT），此时AFM消失，最小值T-N（P-c）= 1.2K。在P下的高能X射线散射测量显示晶格密度逐渐减小，而晶体结构没有任何变化，而NQR频率（nu（Q））的增加表明4f电子和传导电子之间的杂化增加，这稳定了HF-PM状态。T-N降低的AFM相和HF-PM相的形成之间的这种竞争在P-c=2.46 GPa处触发一阶QPT。尽管在P-T相图中缺乏AFM量子临界点，但我们强调了非常规SC发生在AFM和PM两个阶段的事实。原子力显微镜（AFM）相中原子核自旋-晶格弛豫速率为1/T ~（-1），为AFM+SC相的均匀共存提供了证据。值得注意的是，1/T-1的显着增加后，在AFM阶段的冷却揭示了发展的低洼磁激发下降到T-C的AFM阶段，它确实是有关的发病均匀共存的AFM+SC阶段。在HF-PM阶段，AFM波动不发达，1/T-1下降，没有低于Tc的相干峰，其次是幂律的T依赖性，这表明一个非常规的SC与线节点间隙。值得注意的是，T-c在HF-PM相中以及AFM相中在P-c附近具有峰。换句话说，一个SC圆顶存在的最大值T-c=230 mK左右的P-c，表明CeIn 3中的压力诱导HF SC的起源是不相关的AFM自旋波动，但出现的一阶QPT CeIn 3。在CeIn 3中观察到的这些现象应该理解为一阶QPT，因为这些新的物质相是通过施加P诱导的。当AFM临界温度在一阶QPT的终止点处被抑制时，Pc =2.46 GPa，在从AFM到PM的临界点处出现发散的AFM自旋密度波动。CeIn 3导致一种新型的量子临界性的结果值得进一步的理论研究。
We report on pressure-induced unconventional superconductivity (SC) in the heavy-fermion (HF) antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance (NQR) studies conducted under a high pressure. The temperature (T) and pressure (P) dependences of the In-NQR spectra have revealed a first-order quantum-phase transition (QPT) from antiferromagnetism (AFM) to paramagnetism (PM) at a critical pressure P-c=2.46 GPa at which AFM disappears with a minimum value of T-N(P-c)=1.2 K. High-energy x-ray scattering measurements under P show a progressive decrease in the lattice density without any change in the crystal structure, whereas an increase in the NQR frequency (nu(Q)) indicates an increase in the hybridization between 4f electrons and conduction electrons, which stabilizes the HF-PM state. This competition between the AFM phase where T-N is reduced and the formation of the HF-PM phase triggers the first-order QPT at P-c=2.46 GPa. Despite the lack of an AFM quantum critical point in the P-T phase diagram, we highlight the fact that unconventional SC occurs in both phases of AFM and PM. The measurements of the nuclear spin-lattice relaxation rate 1/T-1 in the AFM phase have provided evidence for the uniformly coexisting AFM+SC phase. Remarkably, the significant increase in 1/T-1 upon cooling in the AFM phase has revealed the development of low-lying magnetic excitations down to T-c in the AFM phase; it is indeed relevant to the onset of the uniformly coexisting AFM+SC phase. In the HF-PM phase where AFM fluctuations are not developed, 1/T-1 decreases without the coherence peak just below T-c, followed by a power-law-like T dependence that indicates an unconventional SC with a line-node gap. Remarkably, T-c has a peak around P-c in the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists with a maximum value of T-c=230 mK around P-c, indicating that the origin of the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations but to the emergence of the first-order QPT in CeIn3. These phenomena observed in CeIn3 should be understood in terms of the first-order QPT because these new phases of matter are induced by applying P. When the AFM critical temperature is suppressed at the termination point of the first-order QPT, P-c=2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical point from AFM to PM. The results with CeIn3 leading to a new type of quantum criticality deserve further theoretical investigations.