Elementary excitations in liquid 3He

The two isotopes of helium offer unique opportunities to test fundamental theories of quantum fluids. In the case of liquid 4He, a Bose liquid, the elementary excitations have been studied extensively over the last two decades by neutron inelastic scattering. Similar studies of liquid 3He, the Fermi liquid counterpart of liquid 4He, have become possible only recently. From the results obtained so far for normal liquid 3He the existence of zero sound as a well defined density excitation at finite wave-vectors (q approx. = q/sub F/) and finite temperatures (T approx. = T/sub F/) has been verified and the spin fluctuation spectrum has been measured. By comparing the neutron scattering results for the density fluctuation spectrum to RPA calculations with generalized polarization potentials important information has been obtained about the effective spin-symmetric interaction between 3He atoms. The spin fluctuation spectrum is in agreement with the paramagnon model if a value close to unity is assumed for the contact dimensionless paramagnon parameter anti I. This implies that the nuclear spin system in normal liquid 3He is close to ferromagnetic