Probing the superconducting state of the Heusler supercoductor:   ZrNi$_2$Ga
  Using both muon spin rotation and muon spin relaxation, the superconducting ground state of the Heusler superconductor {ZrNi$_2$Ga} has been studied. The temperature dependence of the magnetic penetration depth of {ZrNi$_2$Ga} is consistent with a single isotropic gap s-wave BCS superconductor. The gap energy is \Delta(0)=0.44(1) meV and the magnetic penetration depth, \lambda(0), is 310(5) nm. Furthermore, we show evidence of a possible cross-over from an square flux line lattice to a hexagonal lattice at low temperatures. No evidence of time reversal symmetry breaking has been observed as might be expected for a half metal superconductor. 
A.D. Hillier, N. Parzyk, D. Mck Paul
cond-mat.supr-con