Electron paramagnetic resonance of ensembles of phosphorus donors in silicon has been detected electrically with externally applied magnetic fields lower than 200 G. Because the spin Hamiltonian was dominated by the contact hyperfine term rather than
by the Zeeman terms at such low magnetic fields, superposition states $ alpha{}| uparrow downarrow >+beta{}| downarrow uparrow >$ and $-beta{}| uparrow downarrow > + alpha{}| downarrow uparrow >$ were formed between phosphorus electron and nuclear spins, and electron paramagnetic resonance transitions between these superposition states and $| uparrow uparrow >$ or $| downarrow downarrow >$ states are observed clearly. A continuous change of $alpha{}$ and $beta{}$ with the magnetic field was observed with a behavior fully consistent with theory of phosphorus donors in silicon.
