Theoretical Study On Superconductivity Of Two Dimensional Boride Hydride

Superconductivity in two-dimensional systems has attracted widespread attention due to its interplay with quantum effects at the two-dimensional limit,which will be important for the realization of next-generation quantum information techniques.With the rapid development of nanotechnology,people have prepared a variety of two-dimensional materials,many of which have superconductivity,such as single-layer B2C,metal-modified/intercalated graphene,and a variety of two-dimensional borides.The superconductivity of metallic hydrogen and hydrogen-rich compounds has always been a research hotspot.Due to the unique physical and chemical properties of hydrogen,it plays an important role in the superconductivity of hydrogen-rich materials.In this paper,We introduced hydrogen atoms into a two-dimensional monolayer boride system(XB₂,X=Ti,Zr,Hf,Sc and Y),and constructed a two-dimensional single-layer borohydride(XB₂H,X=Ti,Zr,Hf,Sc and Y).First principles calculations based on density functional perturbation theory have been used to systematically study the atomic structure,electronic structure and dynamic stability of monolayer two-dimensional borohydride.Using the Migdal-Eliashberg equation under the framework of BCS superconductivity theory,the superconductivity of these systems is discussed,and the influence of external strain on the superconductivity is studied.It is calculated that in the two-dimensional monolayer borohydride(XB₂H,X=Ti,Zr,Hf,Sc and Y)system,the two-dimensional monolayer borohydride(XB₂H,X=Ti,Zr,Hf and Sc)is a kind of thermodynamically stable phonon-mediated superconductor,while the two-dimensional monolayer hydrogenated YB₂H is not thermodynamically stable.Using the effective Coulomb repulsion constant?*=0.01,it is concluded that the highest T_cis monolayer Zr B₂H,because of the large electron-phonon coupling,which is beneficial to the superconducting temperature,the temperature can reach 19 K;the superconducting temperature of monolayer Hf B₂H is 11.87 K;The electron-phonon coupling strength of monolayer Ti B₂H is 0.55,and the T_c is 7.56 K;the minimum T_c of monolayer Sc B₂H is 2.49 K.In addition,the biaxial strain will adjust the T_c.When the structure is stable after stretching,the T_c of monolayer Ti B₂H can reach 16 K at 5%tensile strain;the T_c of monolayer Zr B₂H can reach 23.93 K at 4%tensile strain;monolayer Hf B₂H T_c can reach 19.27 K under 5%tensile stress;the T_c of monolayer Sc B₂H increases with the continuous increase of compressive strain,and the T_cincreases from 2.49 K to 4.1 K.?changes with the change of stress,and finally regulates T_c.T_c has a good correlation with?,indicating that there is phonon-mediated superconductivity in a single-layer two-dimensional borohydride(XB₂H,X=Ti,Zr,Hf and Sc).This research expands our understanding of superconductivity and its potential applications in two-dimensional materials.