Structural and electronic properties of superconducting Heusler alloy Ni$_{2}$Nb$_{1+x}$Sn$_{1-x}$: extit{Ab initio} approach

摘要

Using extit{ab initio} calculation, we investigate systematically thestructural and electronic properties of Ni$_{2}$Nb$_{1+x}$Sn$_{1-x}$ ($x$ = 0,0.25, 0.50). Here, projector augmented wave approach (PAW) implemented in theVienna extit{ab initio} simulation package (VASP) within generalized gradientapproximation (GGA) for the exchange-correlation functional has been used. Inthis article, it is reported that though Ni$_{2}$NbSn andNi$_{2}$Nb$_{1.25}$Sn$_{0.75}$ have no structural transformation,Ni$_{2}$Nb$_{1.5}$Sn$_{0.5}$ can transform to tetragonal structure from cubicL2$_{1}$ phase. The cubic lattice parameter decreases with Nb doping at Snsites in off-stoichiometric alloys. The alloys are in paramagnetic phase in allthe structures. The hybridization between Ni and Nb 3d states triggers thetetragonal distortion. Due to Nb doping in cubic L2$_{1}$ phase, there is asignificant change in total density of states (DOSs) at Fermi energy (E$_{F}$)(N(E$_{F}$)). N(E$_{F}$) increases with increasing Nb doping. But, N(E$_{F}$)decreases during structural transformation of Ni$_{2}$Nb$_{1.5}$Sn$_{0.5}$. Thesuperconducting critical temperature (T$_{C}$) also changes with Nb doping incubic phase and tetragonal distortion because T$_{C}$ very much depends onN(E$_{F}$).