Superconducting gap structure of unconventional superconductors

具有非常规对对称性的超导性一直是超导体物理的中心课题。绝大多数超导体具有传统的s波对称性，具有与整个费米表面上的方向无关的各向同性间隙。在过去的二十年里，人们在重费米子材料、高温铜氧化物和有机化合物中发现了具有不同对称性的非常规超导性。由于超导体的节结结构最终与超导体的对相互作用有关，因此节结结构的确定对于理解超导体的对相互作用机制至关重要.近年来，在相对于晶轴不同方向旋转的磁场中测量超导体的热导率提供了超导体带隙结构的重要信息，包括节结方向.在本项目中，我们测定了PrOs_4Sb_（14）、UPd_2Al_3和CePt_3Si的超导带隙结构。发现超导相中存在着二重对称和四重对称的两种不同的超导相，还发现UPd_2Al_3中反铁磁有序与超导性共存，具有平行于基面的水平线节点。在CePt3Si中，没有空间反转对称性，我们发现了线节点。我们还对非常规超导体CeCoIn 5进行了超声和NMR测量，其中我们在非常低的温度下在上临界场附近发现了一种新的磁通线晶格相。我们提供了第一个令人信服的证据，纹理序参数相的超导体，这是预测约40年前，但从未实验报告到现在为止，尽管在各种超导体的广泛探索。

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.