Collapse of the charge ordering gap of Nd_0.5Sr_0.5MnO₃in an applied magnetic field

We report results of tunneling studies on the charge ordering compound Nd0.5 Sr0.5 MnO3in a magnetic field up to 6 T and for temperature down to 25 K.We show that a gap (2 CO 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.