  Shedding light on the nature of spin-triplet superconductivity has been a
long-standing quest of solid-state physics since the discovery of superfluidity
in liquid $^3$He. Nevertheless, the mechanism of spin-triplet pairing is much
less understood than that of spin-singlet pairing explained by the
Bardeen-Cooper-Schrieffer theory or even observed in high-temperature
superconductors. Here we propose a versatile mechanism for spin-triplet
superconductivity, which is mediated through a melting of macroscopic spin
polarization in weakly coupled odd-gon-unit system (e.g., triangular unit,
pentagon unit, etc). We demonstrate the application of this mechanism by
considering a new class of quasi-one-dimensional superconductors
A$_2$Cr$_3$As$_3$ (A=K, Rb, and Cs). Furthermore, we derive a simple effective
Hamiltonian to easily illustrate the adaptability of the mechanism to general
coupled odd-gon-unit systems. We thus argue that materials consisting of
odd-numbered geometric units would be a prospect of spin-triplet
superconductivity.
