Superconducting gap structure of unconventional superconductors

具有非常规对对称的超导性一直是超导体物理学中的一个中心课题。绝大多数超导体具有传统的s波对称，具有与整个费米表面方向无关的各向同性间隙。近二十年来，人们发现了重费米子材料、高tc铜酸盐和有机化合物具有不同对称性的非常规超导性。由于节点结构最终与配对相互作用有关，因此对其识别对于理解配对机制至关重要。近年来，在相对于晶体轴的不同方向旋转磁场中的热导率测量提供了超导隙结构的重要信息，包括节点方向。在这个项目中，我们确定了PrOs4Sb14， UPd2Al3，和CePt3Si的超导间隙结构，pro4os14是最近发现的一种重费米子超导体，具有填充的角长石结构。我们发现在超导相中存在两种不同的两重对称的超导相和四重对称的超导相，我们还发现UPd2Al3具有平行于基面的水平线节点，其中反铁磁序与超导性共存。在CePt3Si中，没有空间反演对称性，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，在极低温度下，我们在上临界场附近发现了一种新的通量线晶格相。我们提供了超导体中织构有序参数相的第一个令人信服的证据，尽管在各种超导体中进行了广泛的探索，但它在大约40年前就被预测到，但迄今为止从未在实验中报道过。

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.