Session LC05 - Magnetoresistance VI: Orbital and Phase Separation Effects.
FOCUS session, Tuesday afternoon, March 23
Room 367W, GWCC
For certain doping levels in hole-doped manganites, there is a real space charge ordering of the Mn^3+ and Mn^4+ ions when the temperature is reduced below the charge ordering temperature, T_CO^1,2. This ordering of the ions leads to large lattice distortions and a charge ordering gap (2\Delta_CO) opens up in the density of states (DOS) at the Fermi level (E_F)^3. This charge ordered (CO) state can be melted by the application of a magnetic field. Tunneling studies have been carried out on the charge ordering compound Nd_0.5Sr_0.5MnO_3 in a magnetic field up to 6 Tesla and for temperatures down to 25K. The gap (2\Delta_CO \approx 0.5eV) which opens up in the DOS at E_F on charge ordering at T < T_CO (T_CO \sim 150K), collapses in an applied magnetic field when the CO state melts. There is a clear correspondence between the behavior of the resistivity and the gap formation and its collapse in an applied magnetic field. The role of this gap in the DOS at E_F in stabilizing the CO state is discussed.
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