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

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 Delta is strongly anisotropic, varying over a very wide range depending on the contact orientation: the maximum Delta(max) can exceed the minimum Delta(min) 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. (C) 2007 American Institute of Physics.