Study of anisotropic superconductors by means of angle-resolved specific he measurements in magnetic fields

场取向相关的比热C（H，θ）测量是探测非常规超导体节结结构的有力工具。测量的原理是基于理论预测，即在涡旋态中诱导的态的零能量密度作为场与节方向之间的角度的函数而变化。在本计画中，我们研究了各种不同的f电子超导体CeRu_2，PrOs_4Sb_3和URu_2Si_2的节结结构<12>，其摘要如下：1. CeRu_2沿着[100]（[110]）方向上有明显的四重角振荡，并有极大（极小）值。振荡的相对振幅是H和T的强变函数，在低于0.5T和0.3K时为零。根据该系统的各向异性s波场景，这种行为表明沿着[110]方向存在沿着1 K阶的最小间隙。在PrOs_4Sb_中<12>，C（H，θ）在低于Hc ~ 2的整个场范围内沿[100]（[111]）沿着呈现最小（最大）值，表明沿[100]的差距振幅沿着存在深的最小值。然而，当H &lt;&lt;Hc 2时，相对振荡幅度趋于减小，这表明差距完全打开。在超导状态下没有观察到对称性变化的证据。URu_2Si_2的C（H，θ）对H在基面内的旋转没有角度依赖性，表明其节状结构相对于四面体轴具有旋转对称性。发现C（H）随H/Hc 2的变化具有明显的各向异性，表明差距节点主要集中在c方向附近。C（H）的高场行为证明了泡利顺磁损耗效应，表明C（H）具有d波超导性。

Field-orientation dependent specific heat C(H,θ) measurement is a powerful tool to probe the nodal structure of unconventional superconductors. The principle of the measurement is based on the theoretical prediction that the zero energy density of states induced in the vortex state vary as a function of the angle between the field and the nodal directions. In this project, we have examined the nodal structure of various anisotropic f electron superconductors CeRu_2, PrOs_4Sb_<12> and URu_2Si_2, which are summarized as follows.1. For CeRu_2, clear fourfold angular oscillation with maxima (minima) along [100] ([110]) directions have been observed. The relative amplitude of the oscillation is a strongly varying function of H and T, and vanishes below 〜0.5 T and 0.3 K. This behavior indicates the presence of a minimum gap of order 〜1 K along the [110] directions, in accordance with the anisotropic s-wave scenario of this system.2. In PrOs_4Sb_<12>, C(H,θ) exhibits the minima (maxima) along [100] ([111]) in the whole field range below Hc2, indicating a deep minima in the gap amplitude along [100]. The relative oscillation amplitude, however, tends to diminish for H << Hc2, suggesting that the gap is fully opened. No evidence for a symmetry change is observed in the superconducting state.3. C(H,θ) of URu_2Si_2 shows no angular dependence for H rotated in the basal plane, indicating that the nodal structures have rotational symmetry with respect to the tetragonal c axis. A marked anisotropy is found in C(H) as a function of H/Hc2 suggesting that the gap nodes are rather localized near the c directions. Pauli paramagnetic depairing effect is evidenced in the high field behavior of C(H), indicating d-wave superconductivity.