Abstract
Nonreciprocal spin waves can facilitate the realization of spin-wave logic devices. It has been demonstrated that the nonreciprocity can emerge when an external magnetic field is applied to chiral magnets whose spin structures crucially depend on an asymmetric exchange interaction, that is, the Dzyaloshinskii-Moriya interaction (DMI). Here we demonstrate that the nonreciprocity can arise even without the DMI. We demonstrate this idea for the chiral antiferromagnet Ba2NbFe3Si2O14 whose DMI is very small and chiral spin structure arises mainly from the competition between symmetric exchange interactions. We show that when an external magnetic field is applied, an asymmetric energy-gap shift occurs and the spin wave becomes nonreciprocal from the competition between symmetric exchange interactions and the external magnetic field.