We report constraints on the dark photon effective kinetic mixing parameter ($\kappa$) with data taken from two $p$-type point-contact germanium detectors of the CDEX-10 experiment at the China Jinping Underground Laboratory. The 90% confidence level upper limits on $\kappa$ of solar dark photon from 205.4 kg-day exposure are derived, probing new parameter space with masses ($m_V$) from 10 to $300\mathrm{eV}/c^2$ in direct detection experiments. Considering dark photon as the cosmological dark matter, limits at 90% confidence level with $m_V$ from 0.1 to $4.0\mathrm{keV}/c^2$ are set from 449.6 kg-day data, with a minimum of $\kappa =1.3\times {10}^{-15}$ at ${\mathrm{m}}_{\mathrm{V}}=200\mathrm{eV}/{\mathrm{c}}^2$.

• Received 30 October 2019
• Accepted 26 February 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.111301

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Published by the American Physical Society