Direct measurement of the charge ordering gap Nd 0.5 Sr 0.5 MnO 3 in using vacuum tunnelling

We have used tunnelling spectroscopy (TS) to probe the density of states (DOS) of the rare earth manganate Nd0.5Sr0.5MnO3, which shows a transition to a charge ordered (CO) antiferromagnetic insulating state from a ferromagnetic metallic state. We find that a gap opens up in the DOS around the Fermi level, EF, as the solid is cooled below the charge ordering temperature TCO. The charge ordering gap (ΔCO) was found to be strongly temperature dependent for T≈TCO and for T/TCO<0.6 it reaches a limiting value of nearly 0.27 eV. Above TCO the temperature dependence of the DOS at EF was found to be similar to that of the solids such as La0.8Ca0.2MnO3 which show colossal magnetoresistance but no charge ordering.