Spin-dependent splitting of the tunnel conductivity peaks in the magnetic field for junctions involving CDW metals

Abstract

Current-voltage characteristics for junctions involving normal and superconducting charge-density-wave metals in the magnetic field were calculated. Spin splitting was found both for symmetrical and non-symmetrical junctions. r Tunneling between s-wave superconductors (S) and ferromagnets (FM) in the external magnetic field H is a powerful method for studying both electron properties of the paired states and the spin-split band structure of the itinerant electron spectrum [1]. The main practical goal of those investigations consists in the determination of the electron spin polarization P inside the ferromagnet at its Fermi level. The spin splitting of the gap-like maxima in the voltage, V, dependence of the dynamical conductance GðV Þ ¼ dJ=dV , where J is the quasiparticle current, into two components, GðV Þ ¼ G þ ðV Þ þ G À ðV Þ, corresponding to the contributions of current carriers with different spin orientations with respect to the applied field H, is the origin of the effect obtained in the junction device. There is an obstacle, which always acts harmfully in such experiments. It is a strong orbital Meissner effect. To overcome it, a thin-film geometry is used, so that the paramagnetic influence of H on Cooper pairs may manifest itself. The smearing of the G AE ðV Þ maxima by a spin-orbital scattering constitutes another prominent difficulty negatively influencing the method. In this situation, any supplement in the set of gap-possessing objects suitable for probing P would be highly desirable.As those, we propose charge-density-wave (CDW) normal metals and superconductors. Indeed, their paramagnetic properties are very similar to those of s-wave superconductors because due to the electron-hole and electron-electron attraction, respectively, both are in the spin-singlet paired state. That is why the spin splitting of GðV Þ should be like. Nevertheless, one can expect substantial differences since the CDW metals (CDWMs) are gapped only partially, i.e. the nested (d) sections of the Fermi surface (FS) are gapped by the CDW order parameter S ¼ jSje ij , whereas the other FS sections (nd) remain intact at temperatures, T, below the structural transition one, T d [2]. The relative portion of the gapped FS is determined by the parameter 0pmp1.In the magnetic field H, which is large enough to conspicuously move apart the gap-induced maxima G AE ðV Þ but substantially smaller than the so-called paramagnetic limit, H p , one may expect to observe the effect depending also on j. This is a feature distinguishing the CDW case from the superconducting one. One should also note that H p in normal and superconducting CDWMs substantially differs [3] from its Clogston-Chandrasekhar superconducting analog [1]. ARTICLE IN PRESSwww.elsevier.com/locate/physb 0921-4526/$ -see front matter r