  The time-domain (TD) surveys of the Large Sky Area Multi-Object Fiber
Spectroscopic Telescope (LAMOST) yield high-cadence radial velocities, paving a
new avenue to study binary systems including compact objects. In this work, we
explore LAMOST TD spectroscopic data of four K2 plates and present a sample of
six single-lined spectroscopic binaries that may contain compact objects. We
conduct analyses using phase-resolved radial velocity measurements of the
visible star, to characterize each source and to infer the properties of
invisible companion. By fitting the radial velocity curves for the six targets,
we obtain accurate orbital periods, ranging from $\sim$ (0.6-6) days, and
radial velocity semi-amplitudes, ranging from $\sim$ (50-130) km s$^{-1}$. We
calculate the mass function of the unseen companions to be between 0.08 and
0.17 $M_{\odot}$. Based on the mass function and the estimated stellar
parameters of the visible star, we determine the minimum mass of the hidden
star. Three targets, J034813, J063350, and J064850, show ellipsoidal
variability in the light curves from K2, ZTF, and TESS surveys. Therefore, we
can put constraints on the mass of the invisible star using the ellipsoidal
variability. We identify no X-ray counterparts for these targets except for
J085120, of which the X-ray emission can be ascribed to stellar activity. We
note that the nature of these six candidates is worth further characterization
utilizing multi-wavelength follow-up observations.
