  Superconducting strip single-photon detectors (SSPDs) are excellent tools not
only for single-photon detection but also for single-particle detection owing
to their high detection efficiency, low dark counts, and low time jitter.
Although the detection of various particles, including electrons with keV-scale
energy, has been reported so far, there have been no studies for detecting
low-energy electrons. It has yet to be clarified how low-energy electrons
interact with electrons and/or phonons in a superconductor during electron
detection. Here we report the detection property of a superconducting
micro-strip single-electron detector (SSED) for electrons with energy below 200
eV. The detection efficiency is estimated as at least 37 % when electrons
impinging on the stripline possess an energy of 200 eV. We also show that the
minimum detectable energy of electrons is about 10 eV with our SSED, much lower
than those of ions, which implies that the electron-electron interaction plays
a significant role. SSEDs might open a wide range of applications, from
condensed matter physics to quantum information science, because of their
compatibility with the cryogenic environment.
