Collapse of the charge ordering gap of Nd<SUB>0.5</SUB>Sr<SUB>0.5</SUB>MnO<SUB>3</SUB> in an applied magnetic field

We report results of tunneling studies on the charge ordering compound Nd0.5Sr0.5MnO3 in a magnetic field up to 6T and for temperature down to 25 K.We show that a gap (2&#916;CO&#8776;0.5 eV opens up in the density of state (DOS) at the Fermi level (EF) on charge ordering (TCO=150 K) which collapses in an applied magnetic field when the charge ordered state melts. There is a clear correspondence between the behaviour of the resistivity and the gap formation and its collapse in an applied magnetic field. We conclude that a gap in the DOS at EF is necessary for the stability of the charge ordered state