Solitons are important nonperturbative excitations in superfluids. For holographic superfluids, we numerically construct “dark” solitons that have the symmetry-restored phase at their core. A central point is that we include the gravitational backreaction of the matter fields, which becomes important at low temperatures. We study in detail the properties of these solitons under variation of the backreaction strength via tuning the gravitational constant. In particular, the depletion fraction of the particle number density at the core of the solitons is carefully investigated. In agreement with the probe-limit analysis, the depletion fraction shows the same qualitative behavior as in Bogoliubov–de Gennes theory, even if the backreaction is included. We find that the depletion decreases with increasing backreaction strength. Moreover, the inclusion of backreaction enables us to obtain the effective energy density of solitons within holography, which together with an evaluation of the surface tension leads to a simple physical explanation for the snake instability of dark solitons.
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