  In superconductors, electrons with spin ${s=1/2}$ form Cooper pairs whose
spin structure is usually singlet (${S=0}$) or triplet (${S=1}$). When the
electronic structure near the Fermi level is characterized by fermions with
angular momentum ${j=3/2}$ due to strong spin-orbit interactions, novel pairing
states such as even-parity quintet (${J=2}$) and odd-parity septet (${J=3}$)
states become allowed. Prime candidates for such exotic states are half-Heusler
superconductors, which exhibit unconventional superconducting properties, but
their pairing nature remains unsettled. Here we show that the superconductivity
in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by
the admixture of isotropic even-parity singlet and anisotropic odd-parity
septet pairing, whose ratio can be tuned by electron irradiation. From
magnetotransport and penetration depth measurements, we find that carrier
concentrations and impurity scattering both increase with irradiation,
resulting in a nonmonotonic change of the superconducting gap structure. Our
findings shed new light on our fundamental understanding of unconventional
superconducting states in topological materials.
