  We propose a mechanism for detection of a single spin center on a
non-magnetic substrate. In the detection scheme, the STM tunnel current is
correlated with the spin orientation. In the presence of magnetic field, the
spin precesses and the tunnel current is modulated at the Larmor frequency. The
mechanism relies on the effective spin-orbit interaction between the injected
unpolarized STM current and the local spin center, which leads to the nodal
structure of the spatial signal profile. Based on the proposed mechanism, the
strongest spin-related signal can be expected for the systems with large
spin-orbit coupling and low carrier concentration.
