Low Temperature Transport Study On Few Layer 1Td-MoTe₂

Recently,lots of novel physical phenomena,including Weyl fermion,non-saturatedmagnetoresistance,quantumspinHalleffectandIsing superconductivity,have been observed in bulk and monolayer transitional metal dichalcogenides MX2?M=W,Mo and X=Te,Se,S?,which make MX2 a hot topic in condensed matter physics.All of these phenomena arise from the unique spin-orbital coupling and inversion symmetry in MX2.In this thesis,we focused on the study of the superconductivity in few-layer 1Td-MoTe₂ and 1H-NbSe₂.As a rare monolayer superconductor in nature,both of them provide a platform to study superconductivities in two dimensinal limit.Additionally,MoTe₂ is predicted to be a two-dimensional?2D?topological superconductor.Therefore,our studies will be helpful to deepen the understanding of topological superconductivity.The contents of the thesis are as follows:In Chapter 1,we introduce the background on the main topics of Weyl semimental,2D superconductor,and Ising superconductivity.The concept of chiral anomaly,Fermiarc,interfacesuperconductivity,electric-field-induced superconductivity,enhanced upper critical field in Ising superconductivity and quantum metallic state.In Chapter 2,we describe the synthesis method of atomic thin film of MoTe₂ and NbSe₂,the microfabrication process,and the transport measurement equipments including He3 cryostat,PPMS,and diluton refrigerator.In Chapter 3,we focused on low-temperature transport properties of MoTe₂ and NbSe₂.The transport data show that few-layer 1Td-MoTe₂ display enhanced superconductivity with T_c increased 40 times that of its bulk counterpart.The magnetortransport experiments demonstrate that both 1Td-MoTe₂ and NbSe₂ are intrinsic 2D superconductors.More importantly,we find that the in-plane upper critical field is about 6 times that Pauli limit?H_p¹.84 T_c?,and it increases abruptly with the sample thinned down.All of these observations indicate that the electrons in Copper pairs are spin-polarized with its polarization direction along out-of plane direction,which is consistent with Ising superconductivity.We note that this is the first experimental realization of Ising superconductivity in centrosymmetric system.In Chapter 4,we summarize the works of this thesis.