Tunneling Evidence of Half-Metallic Ferromagnetism inLa0.7Ca0.3MnO3

Direct experimental evidence of half-metallic density of states (DOS) is observed by scanning tunneling spectroscopy on ferromagnetic ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$, which exhibits colossal magnetoresistance (CMR). Tunneling conductance data taken at 77 K, well below the Curie temperature $T_C\approx 260\mathrm{K}$, show close resemblance to the spin-split DOS spectrum calculated for the itinerant bands in the ferromagnetic state. The half-metallic spectral characteristics are absent in the paramagnetic state at room temperature, as well as in the undoped antiferromagnetic compound ${\mathrm{LaMnO}}_3$, which shows no CMR. These results directly implicate the half-metallic ferromagnetism in the phenomenon of CMR.