Search for Light Dark Matter with Ionization Signals in the PandaX-4T Experiment

We report the search results of light dark matter through its interactions with shell electrons and nuclei, using the commissioning data from the PandaX-4T liquid xenon detector. Low energy events are selected to have an ionization-only signal between 60 to 200 photoelectrons, corresponding to a mean nuclear recoil energy from 0.77 to 2.54 keV and electronic recoil energy from 0.07 to 0.23 keV. With an effective exposure of 0.55  tonne·year, we set the most stringent limits within a mass range from 40  MeV/c^{2} to 10  GeV/c^{2} for pointlike dark matter-electron interaction, 100  MeV/c^{2} to 10  GeV/c^{2} for dark matter-electron interaction via a light mediator, and 3.2 to 4  GeV/c^{2} for dark matter-nucleon spin-independent interaction. For DM interaction with electrons, our limits are closing in on the parameter space predicted by the freeze-in and freeze-out mechanisms in the early Universe.