Superconducting gap structure of unconventional superconductors

具有非传统配对对称性的超导电性一直是超导体物理学的中心课题。绝大多数超导体具有传统的S波对称性，具有与整个费米面方向无关的各向同性带隙。在过去的二十年里，人们发现了具有不同对称性的非常规超导电性：重费米子材料、高T_c铜酸盐和有机化合物。由于结点结构最终与结对相互作用有关，因此结点结构的识别对于理解结对机制至关重要。最近，磁场相对于晶轴旋转不同方向的热导率测量提供了包括结点方向在内的超导带隙结构的重要信息。在这个项目中，我们已经确定了PrOs4Sb14，UPd2Al3和CePt3Si的超导带隙结构，PrOs4Os14是最近发现的填充Skutterdite结构的重费米子超导体。我们发现在超导相中存在两种不同的具有两重和四重对称性的超导相，我们还发现UPd2Al3具有平行于基面的水平线节，其中反铁磁有序与超导共存。在没有空间反转对称性的CePt3Si中，我们发现了线节点。我们还对非常规超导体CeCoIn5进行了超声和核磁共振测量，在很低的温度下，我们在上临界场附近发现了一种新的磁通线晶格相。我们首次提供了超导体中织构有序参数相的令人信服的证据，尽管在各种超导体中进行了广泛的探索，但这一点在大约40年前就被预测出来了，但到目前为止还没有实验报道。

Superconductivity with unconventional pairing symmetry has been a central subject in the physics of superconductors. The vast majority of superconductors have conventional s-wave symmetry with an isotropic gap which is independent of directions over the entire Fermi surface. In the last two decades unconventional superconductivity with different symmetry has been found heavy fermion materials, high-Tc cuprates, and organic compounds. Since the nodal structure is ultimately related to the pairing interaction, its identification is crucial for understanding the pairing mechanism.Recently, thermal conductivity measurements in magnetic field inrotating various directions relative to the crystal axis provide an important information of the superconducting gap structure, inclusing the nodal directions. In this project, we have determined the superconducting gap structure in PrOs4Sb14, UPd2Al3, and CePt3Si, PrOs4Os14 is a recently discovered heavy fermion superconductor with filled skutterdite structure. We found that there are two different superconducting phases with two and four fold symmetry in the superconducting phase, We also showed that UPd2Al3, in which antiferomagnetic order coexists with superconductivity, has horizontal line nodes parallel to the basal plane. In CePt3Si, with no spatial inversion symmetry, we found line nodes.We also performed ultrasound and NMR measurements on the unconventional superconductor CeCoIn5, wherein we find a novel flux line lattice phase in the vicinity of the upper critical field at very low temperatures. We provide the first compelling evidence of a textured order parameter phase in superconductors, which was predicted some 4 decades ago but never reported experimentally up to now, in spite of extensive exploration in various superconductors.