Orbital-Order-Induced Metal-Insulator Transition inLa1−xCaxM

Abstract

We present evidence that the insulator-to-metal transition in La(1-x)Ca(x)MnO3 near x approximately 0.2 is driven by the suppression of coherent Jahn-Teller distortions, originating from d-type orbital ordering. The orbital-ordered state is characterized by large long-range Q2 distortions below T(O'- O*). Above T(O'- O*) we find evidence for coexistence between an orbital-ordered and an orbital-disordered state. This behavior is discussed in terms of electronic phase separation in an orbital-ordered insulating and an orbital-disordered metallic state.

Effect of disorder in an orbitally ordered Jahn-Teller insulator

“…Hole doping leads to progressive loss of orbital order (OO), a reduction of the transport gap, increasing isotropy in the effective magnetic exchange, and an insulator (I) to metal (M) transition [2,18,19]. Beyond transport and thermodynamic indicators, NMR and neutron scattering experiments have revealed an inhomogeneous -possibly phase separated -state in the low doping regime [20,21].…”

“…Upon hole doping, e.g. in La 1−x Ca x MnO 3 , the system evolves via a ferromagnetic insulating phase towards an orbitally disordered (OD) ferromagnetic metal, which exhibits colossal magnetoresistance (CMR) near the Curie temperature [2]. Quenched disorder has been widely acknowledged as a crucial ingredient for the understanding of hole-doped manganites [3,4].…”

Raman spectra in epitaxial thin films ofLa1−xCaxMnO3(Xiong1, Chen2, Wang3 et al. 2004Phys. Rev. B502232View full textAdd to dashboardCite

“…Particularly, La 1−x Ca x M nO 3 has a very rich phase diagram of ground states with competing order parameters 5,6 . The parent compound is LaM nO 3 , which belongs to the family of rotationally distorted perovskites 7 and is an anti-ferromagnetic (AFM) insulator. With the increase of doped Ca 2+ content, CMR has been observed in the Ca concentration of 0.2-0.5 8 .…”

Charge-transfer induced surface conductivity for a copper based inorganic-organic hybrid

“…Therefore, the doping removes the charge carrier blockade of the antiferrodistortive arrangement of the d͑z 2 −x 2 ͒ and d͑z 2 −y 2 ͒ type orbitals, as has been extensively studied for perovskite-based layered Cu-and Mn-oxides. 15 The doping results in a higher conductivity, because it both introduces extra carriers and promotes greater delocalization. Due to the electron doping the magnetic moment at the TTF-hybrid interface is partially canceled.…”