| The proximity effect has been a central subject of superconductivity research for decades.Superconductivity correlation is introduced to the normal side of a superconductor（S）-normal metal（N）junction through a process known as the Andreev reflection（AR）,where an incident electron is reflected back as a hole.Current condensed matter research exploits the superconducting proximity effect to engineer exotic interfacial quantum phenomena.such as mysteriously topological superconductivity induced in the topological insulator/s-wave superconductor interfaces,multiple differential conductance peaks in Nb Se2/Graphene heterostructures,8-10 and induced superconductivity in Dirac/Weyl semimetals.The ever expanding family of van der Waals metals,superconductors,topological insulators,and ferromagnets makes a compelling case to explore the proximity effect in van der Waals S-N junctions.Especially for the layered vd W materials can be easily exfoliated and stacked together to form the heterostructures,which is regarded as the promising playground for the exploration of the superconducting proximity effect.In this dissertation,we have performed systematic study of the magneto transport properties of vd W 2H-Ta S2/Nb Se2 heterostructures of it under low temperature and applying external magnetic field conditions.with decreasing temperature,an evident resistance drop occurs at～6.9 K（*）at zero B-field,followed by a resistance upturn at～6.7 K and the second resistance drop at～2.9 K（）,coincided with the temperature of phase transition of Nb Se2,enhanced Ta S2,respectively.The two peaks（A*and B*）shift to low current value with the increases of the applied B-fields as expected.However,compared to the evolution of A peak in Nb Se2 flakes,the decrease trend of A*peak versus the applied B-fields is slower than that of A peak,in which the critical current of A*peak is larger than that of A peak in the B-filed range of 0.5–3 T.In addition,the critical current of peak B*is slightly larger than that of peak B observed in Nb Se2 flakes.Such unique enhancement is believed to be originated from the enhanced pair strength in the Cooper pair of the Nb Se2 flakes due to the complex interfacial coupling between the Nb Se2 flakes and 2H-Ta S2 flakes.When the heterojunction is parallel to the external magnetic field,the upper critical magnetic field on Heterojunction at zero temperature is larger than that at 1.8 K.It may be due to spin orbit coupling and it is in accordance with the relationship between the upper critical magnetic field and temperature in a general S wave superconductor.However,which is not corresponding to the behavior of decreasing of the upper critical magnetic field in general superconductors with the increase of temperature,because the upper critical magnetic field on the intrinsic Nb Se2 and 2H-Ta S2 at zero temperature is larger than that at 1.8 K,but the specific mechanism is not clear.The anisotropy ratios of Nb Se2,2H-Ta S2 and heterojunction are 3.69,19.75 and 7.45 respectively,which indicates that Nb Se2,2H-Ta S2 and heterojunction are anisotropic superconductors. |
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