Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
Phys Rev Lett. 2014 Feb 14;112(6):067002. doi: 10.1103/PhysRevLett.112.067002. Epub 2014 Feb 12.
Superconductivity in the heavy-fermion compound CeCu2Si2 is a prototypical example of Cooper pairs formed by strongly correlated electrons. For more than 30 years, it has been believed to arise from nodal d-wave pairing mediated by a magnetic glue. Here, we report a detailed study of the specific heat and magnetization at low temperatures for a high-quality single crystal. Unexpectedly, the specific-heat measurements exhibit exponential decay with a two-gap feature in its temperature dependence, along with a linear dependence as a function of magnetic field and the absence of oscillations in the field angle, reminiscent of multiband full-gap superconductivity. In addition, we find anomalous behavior at high fields, attributed to a strong Pauli paramagnetic effect. A low quasiparticle density of states at low energies with a multiband Fermi-surface topology would open a new door into electron pairing in CeCu2Si2.
在重费米子化合物 CeCu2Si2 中观察到的超导现象是强关联电子形成库珀对的典型范例。三十多年来，人们一直认为它是由磁性胶介导的节点 d 波配对引起的。在这里，我们报告了对高质量单晶在低温下的比热和磁化率的详细研究。出乎意料的是，比热测量显示出随温度呈指数衰减的特征，具有双能隙特征，并且作为磁场的函数呈线性关系，在磁场角度上没有振荡，类似于多能带全能隙超导性。此外，我们在高场下发现了异常行为，归因于强的泡利顺磁效应。在低能量下具有多能带费米面拓扑结构的低准粒子态密度将为 CeCu2Si2 中的电子配对开辟新的途径。
