A recent, major, puzzle in the core-level photo emission spectra of
doped manganites is the observation of a 1-2 eV wide shoulder with
intensity varying with temperature T as the square of the
magnetization over a T scale of order 200K, an order of magnitude
less than electronic energies. In this talk I discuss a recent
theory we have developed* to address and resolve this puzzle, by
extending the recently proposed (localized-polaron +
mobile-electron) two fluid model for manganites to include core-hole
effects. The shoulder seems to arise from a broadened X-ray edge
singularity whose exponent varies with temperature, reflecting the
rapid redistribution of the spectral density of the mobile electrons
due to their strong scattering from thermally disordered t2g
core spins. Furthermore, our theory leads to a correspondence
between spectral changes due to increasing doping and decreasing
temperature, as experimentally observed.
(* work done in collaboration with Prabuddha Sanyal, Subhra Sen
Gupta, Nandan Pakhira, D. D. Sarma and T. V. Ramakrishnan
( http://arxiv.org/abs/0704.3923), and to be published)