The $mu$eV-mass axion is one of the most promising candidates for cold dark matter, and remains to be a well-motivated solution to the CP problem of Quantum Chromodynamics (QCD) via the Peccei-Quinn mechanism. In this paper, we propose a novel method to detect the dark-matter axions in our galaxy via the resonant emission $|{rm e}rangle to |{rm g}rangle + gamma + gamma^{prime}_{} + a$ (or absorption $a + |{rm e}rangle to |{rm g}rangle + gamma + gamma^{prime}_{}$) in an atomic system with superradiance, where $|{rm e}rangle$ and $|{rm g}rangle$ stand for the excited and ground energy levels of atoms, respectively. A similar process via $|{rm e}rangle to |{rm g}rangle + gamma + a$ (or $a + |{rm e}rangle to |{rm g}rangle + gamma$) is also put forward to probe the axion-electron coupling. For the nominal experimental setup assuming a background-free environment, most of the parameter space for typical QCD axion models can be covered with parahydrogen molecules or ytterbium atoms. However, the background in a realistic experimental setup remains to be a major issue that needs to be solved in future studies. Searching for better atomic or molecular candidates may be required for a bigger signal-to-noise ratio.
Download