Superconductivity in the doped topological insulator CuxBi2Se3

Possible unconventional superconductivity in CuxBi2Se3, believed to be a topological superconductor, is examined. Using methods from group theory, the allowed superconducting states are classified according to their behaviour under the crystal symmetry transformations. The Josephson coupling between unconventional and conventional superconductors is discussed and used to propose SQUID-like experiments that can distinguish the different superconducting states. It has been attemped to use a Scanning SQUID Microscope to show superconductivity in akes of CuxBi2Se3 as a first step towards these experiments. Although this has not been achieved, some interesting results have to be mentioned. SSM measurements on samples with akes of CuxBi2Se3 showed that it is very difficult to determine the position of the sensor with respect to the sample. However, when a random pattern of niobium is deposited on the sample, it is possible to determine it. In order to show superconductivity in akes of CuxBi2Se3 with a four-point measurement, contacts on the akes have to be made at a lower temperature than 100 ◦C. In the photolithography process, a new recipe for making a photoresist structure has been developed. The highest temperature in this process is now 65 ◦C. Although the recipe can still be improved, it is now possible to fabricate contacts without heating the akes too much, which is believed to destroy their superconductivity.