  Spin-triplet superconductivity is known to be a rare quantum phenomenon. Here
we show that nonsymmorphic crystalline symmetries can dramatically assist
spin-triplet superconductivity in the presence of spin-orbit coupling. Even
with a weak spin-orbit coupling, the spin-triplet pairing can be the leading
pairing instability in a lattice with a nonsymmorphic symmetry. The underlining
mechanism is the spin-sublattice-momentum lock on electronic bands that are
protected by the nonsymmorphic symmetry. We use the nonsymmorphic space group
P4/nmm to demonstrate these results and discuss related experimental
observables. Our work paves a new way in searching for spin-triplet
superconductivity.
