Spin-excitons in heavy-fermion semimetals

•We discuss the theory of spin excitons in heavy-fermion semiconductors as precritical fluctuations.•We show that relatively sharp magnetic in-gap excitations can also occur in semiconductors.•The magnetic excitations are only sharp for a restricted range of center of mass momenta.•They may merge with the quasi-elastic peak associated with incommensurate nesting of electron and hole pockets.

Spin-excitons are sharp and dispersive magnetic fluctuations in paramagnetic semiconductors where the dispersion relation lies within the semiconducting gap. Spin-excitons are found in the vicinity of magnetic quantum critical points in semiconductors, much the same as antiparamagnons are precursor fluctuations for quantum critical points in metals. Here we show that this concept of spin-exciton excitations can be extended to heavy-fermion semimetals and provides a natural explanation of the magnetic modes found by inelastic neutron scattering experiments on paramagnetic CeFe2Al10.