Studies of Symmetry of Order parameter of non-BCS superconductors by low temperature scanning tunneling microscopy and spectroscopy

我们研制了低温扫描隧道显微镜，它可以在高达12T的强磁场下进行能量分辨率优于10μeV、原子空间分辨率低于1K的扫描隧道谱测量。结合我们研制的STM探针和3He-4He稀释式制冷机，我们现在已经准备好在0.1K的温度范围内进行STS/STM。利用所研制的STS装置，我们对非BCS超导体的可能候选者进行了STS研究，如Bi2Sr2CaCu2Ox、YNi2B2C、CeRu_2、UPd2Al3、CeCoIn_5、Sr2RuO4和MgB_2。在Bi2Sr2CaCu2Ox、YNi2B_2C、CeRu2中，我们成功地观测到了涡旋。用LT-STS研究了超导体库珀配对的轨道对称性。在多晶MgB_2中，从颗粒到颗粒的STS测量表明，MgB_2是具有两个能隙的超导体，可以用两带超导体来解释。我们已经指出LT-STS/STM是研究超导电性的一种非常有效的方法。

We have developed low temperature scanning tunneling microscope (LT-STM) with which we are able to perform scanning tunneling spectroscopy (STS) with energy resolution better than 10 μeV with an atomic spatial resolution below 1K in high magnetic fields up to 12 T. At 0.45K the precise STS/STM measurements were able to be performed. Combining our developed STM probe with 3He-4He dilution refrigerator, we are now ready for STS/STM in the temperature region of 0.1K. By using thus developed STS apparatus, we have made STS studies of possible candidates of non-BCS superconductors such as Bi_2Sr_2CaCu_2O_x, YNi_2B_2C, CeRu_2, UPd_2Al_3, CeCoIn_5, Sr_2RuO_4 and MgB_2. In Bi_2Sr_2CaCu_2O_x, YNi_2B_2C, CeRu_2 we have succeeded in observing vortices. The orbital symmetries of Cooper pairing of the superconductors have been studied by LT-STS. In polycrystalline MgB_2 STS measurements were performed from grain to grain and MgB_2 have been found to be a superconductor with 2 energy gaps which can be interpreted in terms of 2-band superconductor. We have indicated that LT-STS/STM is quite a powerful method for superconductivity studies.