  Quasi-one-dimensional $A_2\text{Cr}_3\text{As}_3$ (with $A = \text{K, Cs,
Rb}$) is an intriguing new family of superconductors which exhibit many similar
features to the cuprate and iron-based unconventional superconductor families.
Yet in contrast to these systems, no charge or magnetic ordering has been
observed which could provide the electronic correlations presumed necessary for
an unconventional superconducting pairing mechanism - an absence which defies
predictions of first principles models. We report the results of neutron
scattering experiments on polycrystalline $\text{K}_2\text{Cr}_3\text{As}_3$
$(T_c \sim 7\text{K})$ which probed the low temperature dynamics near $T_c$ .
Neutron diffraction data evidence a strong response of the nuclear lattice to
the onset of superconductivity while inelastic scattering reveals a highly
dispersive column of intensity at the commensurate wavevector $q =
(00\frac{1}{2})$ which loses intensity beneath $T_c$ - indicative of
short-range magnetic fluctuations. Using linear spin-wave theory we model the
observed scattering and suggest a possible structure to the short-range
magnetic order. These observations suggest that
$\text{K}_2\text{Cr}_3\text{As}_3$ is in close proximity to a magnetic
instability and that the incipient magnetic order both couples strongly to the
lattice and competes with superconductivity - in direct analogy with the
iron-based superconductors.
