Research On Low Temperature Transport Property Of MoTe₂/Nb Josephson Junction

Recently,the topological superconductor was proposed,as a new state of quantum matter which is distinctively different from conventional superconductors.The topological superconductor hosts mysterious Majorana fermions,which obey non-abelian statistics and are thus of great importance in the topological quantum computation.Therefore,the study of topological superconductors is now one of the hottest topics in condensed matter physics and material science.It's also predicted that such a topological superconducting state can be realized in heterostructures composed of s-wave superconductor and topological material by combining the superconductivity and strong spin-orbit interaction.In this dissertation,we have performed systematic study of the superconducting proximity effect and Josephson effect in type-II Weyl semimetal MoTe₂.We have fabricated Nb-MoTe₂-Nb Josephson junction by electron beam lithography and then measured the transport properties of it under low temperature and magnetic field conditions.As temperature decreases,the device resistance drops sharply at the superconducting transition temperature of Nb?? 9 K?.But at 3.2 K,another rapid decrease of resistance is observed.Above 3.2 K,the differential resistance curve is smooth and flat,without any feature.But when the temperature is below 3.2 K,there is obvious decrease of the differential resistance within the voltage range |V |<?_L.Besides this,the differential resistance drops more rapidly when |V |<?_S,where ?_S<?_L.It is believed that these features indicate the emergence of Andreev reflection and the superconducting proximity effect has induced superconducting gaps e?_L and e?_S in the surface and bulk states of MoTe₂,respectively.We have also used the BCS theory to fit the obtained ?_L & ?_S at different temperatures.From the fitting,the induce zero-temperature superconducting gaps for the surface and bulk states are 0.41 me V and 0.11 me V,respectively.Furthermore,with temperatures decreasing below 2.7 K,the differential resistance spectrum exhibits another very sharp dip around zero bias.The measured current-voltage curve also resembles the supercurrent behavior generally observed in Josephson junctions.All these lead us to believe that we have observed the DC Josephson effect in our Nb-MoTe₂-Nb device at low temperatures?T< 2.7 K?.Our work will pave the way for future study of possible topological superconductivity or Majorana fermions in Weyl semimetals.