Single spin ESR

On the basis of classical scanning tunneling microscopy a new technique, single spin tunneling spectroscopy, is developed and experimentally illustrated. It allows to detect singlet and triplet channels of the tunneling current corresponding to the spin states of the pair of tunneling and unpaired electrons. The current of polarized tunneling electrons emitted by ferromagnetic tip may be controlled by resonance microwaves and allows to monitor the ESR spectrum of a single paramagnetic center. Theory of the new phenomenon is developed as a guide to the single spin ESR experimental devices.