  Inhomogeneous superconductivity in the high quality single crystals of ZrB12
(Tc = 6 K) has been studied using the heat capacity and x-ray diffraction (XRD)
data. Evidence of two-band superconductivity with two branches of upper
critical field Hc2(Tc) is obtained in a magnetic field applied along the [110]
axis of the crystal. On the contrary, at H //[100], the only dependence Hc2(Tc)
is observed. This finding is supplemented with the checkerboard-type patterns
of the charge stripes in ZrB12 deduced from the detailed analysis of XRD data.
These patterns are compared to the structure of the charge stripes in the
weakly bound superconductor LuB12, whose Tc is 15 times lower than that of
ZrB12. Probable nature of the two-gap superconductivity in ZrB12 with strongly
enhanced characteristics is discussed.
