Although dark matter makes up about 85% of the universe’s matter, it remains one of the greatest mysteries in modern physics. Light dark matter particles—those with masses lighter than that of a proton—are an important class of dark matter candidates. They could be thermally produced in the early universe and are predicted by many new physics models. Observing the interactions between light dark matter particles and ordinary matter may lead to revolutionary breakthroughs in the field of direct dark matter detection. However, the signals produced by such interactions in this low-mass range are extremely weak, presenting major challenges for experimental detection.
Recently, Dr. Liang Zhengliang from theCollege of Mathematics and Physics at Beijing University of Chemical Technology, in collaboration with partners, proposed an innovative detection paradigm based on the plasmon effect in semiconductor detectors, opening up a new path to overcome the challenges in detecting light dark matter. This work focuses on the resonance feature of collective electron oscillations in solid-state dark matter detectors , which enables the most sensitive detection so far for dark matter particles in the mass range of 1 keV to 1 MeV. The related findings were published in Physical Review Letters, under the title “Plasmon-Enhanced Direct-Detection Method for Boosted Sub-MeV Dark Matter.”
Figure. Light dark matter particles accelerated by cosmic rays can excite plasmon signals in Skipper-CCD based semiconductor detectors, and thus be detected.
Plasmons are quasiparticle excitations formed by collective oscillations of electrons in solid detectors (analogous to phonons in lattice vibrations). When high-energy dark matter particles penetrate a material, they can excite plasmons, which then decay into multiple electron-hole pairs that can be detected. The research team developed a comprehensive analytical framework integrating relativistic dark matter particle dynamics, non-relativistic many-body electron system theory, and first-principles calculations, systematically revealing the microscopic process of plasmon excitation by dark matter. The study shows that the typical thermal velocity of dark matter in the Milky Way halo (~0.001 the speed of light) is insufficient to excite plasmons in semiconductors like silicon and germanium. However, high-velocity dark matter particles can effectively trigger plasmon responses. By analyzing data from the SENSEI and DAMIC experiments, which are based on the Skipper-CCD technology, the team set the tightest constraints to date on the coupling strength between dark matter and electrons in the mass range of 1 keV to 1 MeV. This result not only validates the effectiveness of the proposed theoretical approach but also reveals the potential of existing semiconductor detectors—when traditional nuclear recoil detection is limited by energy thresholds, plasmon effects can significantly enhance the sensitivity to dark matter detection. This provides crucial theoretical support for the design of next-generation international light dark matter direct detection experiments such as OBSCURA.
Dr. Liang Zhengliang from College of Mathematics and Physics of Beijing University of Chemical Technology is the first author and corresponding author of the paper. Professor Wu Lei and his PhD student Su Liangliang from Nanjing Normal University, and Professor Zhu Bin from Yantai University are the co-corresponding authors, with Beijing University of Chemical Technology listed as the first affiliation.
Paper link: https://doi.org/10.1103/PhysRevLett.134.071001
Author Introduction:
Liang Zhengliang：Lecturer at the College of Mathematics and Physics, Beijing University of Chemical Technology. His research focuses on dark matter particle phenomenology.