  The discovery of pressure-induced superconductivity in helimagnets (CrAs,
MnP) has attracted considerable interest in understanding the relationship
between complex magnetism and unconventional superconductivity. However, the
nature of the magnetism and magnetic interactions that drive the unusual
double-helical magnetic order in these materials remains unclear. Here, we
report neutron scattering measurements of magnetic excitations in CrAs single
crystals at ambient pressure. Our experiments reveal well defined spin wave
excitations up to about 150 meV with a pseudogap below 7 meV, which can be
effectively described by the Heisenberg model with nearest neighbor exchange
interactions. Most surprisingly, the spin excitations are largely quenched
above the Neel temperature, in contrast to cuprates and iron pnictides where
the spectral weight is mostly preserved in the paramagnetic state. Our results
suggest that the helimagnetic order is driven by strongly frustrated exchange
interactions, and that CrAs is at the verge of itinerant and
correlation-induced localized states, which is therefore highly
pressure-tunable and favorable for superconductivity.

Superconductivity;Materials Science;Strongly Correlated Electrons