Magnetic solitons in Rabi-coupled Bose-Einstein condensates

We study magnetic solitons, solitary waves of spin polarization (i.e., magnetization), in binary Bose-Einstein condensates in the presence of Rabi coupling. We show that the system exhibits two types of magnetic solitons, called 2 pi and 0 pi solitons, characterized by a different behavior of the relative phase between the two spin components. 2 pi solitons exhibit a 2 pi jump of the relative phase, independent of their velocity, the static domain wall explored by Son and Stephanov being an example of such 2 pi solitons with vanishing velocity and magnetization. 0 pi solitons instead do not exhibit any asymptotic jump in the relative phase. Systematic results are provided for both types of solitons in uniform matter. Numerical calculations in the presence of a one-dimensional harmonic trap reveal that a 2 pi soliton evolves in time into a 0 pi soliton, and vice versa, oscillating around the center of the trap. Results for the effective mass, the Landau critical velocity, and the role of the transverse confinement are also discussed.