Electron Spectroscopy of Correlated Transition Metal Oxides

Abstract

It is now realized that electron—electron Coulomb repulsion (electron correlation) strength, U plays the key role in determining the electronic properties of various condensed matter systems. Employing photoelectron spectroscopy, it is observed that the surface and bulk electronic structures can be significantly different in transition metal oxides. One can extract the surface and bulk spectra using variation of surface sensitivity of the technique with the incident photon energies. The bulk spectra in various transition metal oxides show that the magnitude of U reduces with the increase in radial extension of the associated orbitals as expected due to their inverse relation [U(3d) ≤U(4d) ≤U(5d)]. However, U is also found to depend on associated crystallographic structures. Particle-hole asymmetry, disorder in these correlated systems leads to plethora of novel properties. In higher d systems, electron—lattice, electron—magnon couplings become more important, which could be probed using high energy resolution photoemission technique. Interestingly, the insulating behavior observed in 5d transition metal oxides often does not correspond to a gapped state.