Andreev reflection study of the new magnetic superconductor Mo3Sb7: evidence of gap anisotropy

Abstract

Point-contact (PC) Andreev-reflection experiments on the new paramagnetic superconductor Mo3Sb7 are reported for which we have observed strong distinctions in the PC spectra measured for different contact axis orientations. Analysis of the PC spectra in the framework of the Blonder–Tinkham–Klapwijk theory has shown that the gap parameter Δ is strongly anisotropic, varying over a very wide range depending on the contact orientation: the maximum Δmax can exceed the minimum Δmin by at least 40 times. For these and other reasons we suggest that Mo3Sb7 is not a trivial BCS (s-wave) superconductor but rather has (s+g)-wave or another unconventional pairing symmetry.

Andreev reflection study of the new magnetic superconductor Mo3Sb7 in magnetic field

“…So, the highest D is observed in the contacts oriented along the crystallographic directions where the gap function has a maximum. In the other so-called nodal directions with zero or close-to-zero gap function the spectra reveal the many times lower D. As before [4], we believe that the behavior of D for the lobe directions (i.e., corresponding to the maxima of gap function) with a change of temperature or magnetic field is roughly similar to that observed in conventional s-type superconductors with an isotropic gap function. Indeed, the experimental dependences D( ) T (Fig.…”

“…A similar situation occured while measuring the temperature dependence of the order parameter of Mo Sb 3 7 in [4], where it was assumed that this superconductor has anisotropic symmetry of pairing, e.g., of the d-or sg-type. So, the highest D is observed in the contacts oriented along the crystallographic directions where the gap function has a maximum.…”

“…(The effect is not discussed in this work.) The rather large amplitude of the zero-bias minimum at H ; 7 4 . kOe (Fig.…”

“…The point-contact spectra of the Andreev reflection in metallic (no dielectric barriers) Ag-Mo Sb 3 7 contacts, measured at different temperatures, are presented in Ref. 4. They are seen to vary considerably from contact to contact.…”

Effect of the tetragonal distortion on the electronic structure, phonons and superconductivity in the Mo3Sb7 superconductor

“…specific heat, NMR or µSR) to reveal the gap symmetry under pressure should shed some light on the pairing symmetry. Especially, that Andreev reflexion studies [53,54] in Mo 3 Sb 7 even at ambient pressure suggested non-BCS strong gap anisotropy, with possible s+g gap symmetry.…”