Orbital order induced metal-insulator transition in (La,Ca)MnO3

We present evidence that the insulator to metal transition in (La,Ca)MnO3 near x~0.2 is driven by the suppression of coherent Jahn-Teller distortions, originating from d type orbital ordering. The orbital ordered state is characterised by large long-range Q2 distortions below To*-o’. Above To*-o’ we find evidence for coexistence between an orbital-ordered and -disordered state. This behaviour is discussed in terms of electronic phases of an orbital ordered insulating and orbital-disordered metallic states.