Research On The Superconductivity Of Ultra-thin Heterojunction Composed Of Pb And MoTe₂

Inspired by graphene,two-dimensional materials are experiencing a great surge of research interest in the field of materials science because of their novel physics properties.We can get new physical properties by stacking different two-dimensional materials.MoTe2 is a typical transitional metal dichalcogenides material,Pb is a conventional superconductor.In this paper,we construct the ultrathin heterostructures by stacking monolayer MoTe2 and monolayer Pb due to its following characters:(l)the lattice mismatch between Pb((111)plane is 3.5A)and MoTe2(lattice constant 3.52A)is very small.(2)due to the breaking of inversion symmetry,Te and Pb are heavy elements,resulting in the heterosfructure by stacking monolayer MoTe2 and monolayer Pb has large asymmetric spin-orbit coupling.In this paper,the asymmetric SOC impacts on electronic structure and superconductivity of the heterostructure are investigated via first-principles calculations based on Density Functional Theory.The result of two heterostructures we obtained as follows:(1)The lattice dynamics,spin-resolved electron-phonon interaction and superconducting properties of Pb(1ML)/MoTe2(1ML)heterostructure.The calculation of phonon dispersion indicates its dynamical stability.The crystal momentum K-dependent electron-phonon interaction is studied by Migdal-Eliashberg theory.Both large in-plane Rashba spin splitting hole bands near ? point and large out-of-plane spin splitting electron bands near K point have considerable electron-phonon strength.The electron-phonon coupling displays significant anisotropy.The superconducting critical temperature Tc is predicted to be 4.0-6.7K.(2)The geometric structure,spin-resolved band structure,electron-phonon interaction and superconducting properties of Pb(1 ML)/MoTe2(1 ML)/Pb(1 ML)heterostructure.The energetically stable configuration for the heterostructure is/CABAC/.Because of the mirror symmetry,in-plane Rashba spin splitting near? point disappears.The same as the Pb(1ML)/MoTe2(1ML)heterostructure,due to the time reversal symmetry between the K and K' points,the out-of-plane spin-polarization orientation is reversed.The values of two spin splitting electron bands at the K point are 364meV and 263meV.The crystal momentum K-dependent electron-phonon interaction and superconducting gap are calculated and the results display significant anisotropy.The superconducting critical temperature Tc is predicted to be 6.3-10.0K.This value is larger than the value when isotropic Migdal-Eliashberg equation is used to estimate the superconducting transition temperature,We think that the isotropic Migdal-Eliashberg equation is inadequate.Due to the complex Fermi surface in this low-dimensional system,The temperature dependence of the superconducting gap of the Pb(1ML)/MoTe2/Pb(1ML)can be fitted by solving the BCS gap equation numerically,suggesting a BCS mechanism by phonon-mediated as its superconducting origin.Due to the significant anisotropy of electron-phonon interaction,different parameter ? is used at different temperature.The research show that strong spin-orbit coupling and broken of inversion symmetry in two heterostructures lead to large Rashba spin splitting,the asymmetric spin-orbit coupling may induce non-conventional superconducting properties,suggesting the two heterostructures are potential topological superconductors.