Collapse of the charge ordering gap of Nd0.5Sr0.5MnO3 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 6 T and for temperature down to 25 K. We show that a gap (2 Delta(CO) approximate to 0.5 eV opens up in the densi ty of state (DOS) at the Fermilevel (E-F) on charge ordering (T-CO = 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 resist ivity and the gap formation and its collapse in an applied magnetic field. We conclude that a gap in the DOS at E-F is necessary for the stability of the charge ordered state.