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"Ab-initio (LDA+DMFT) description of CMR pyrochlore Tl2Mn2O7"

Relatore: Dr. Cecilia I. Ventura, Centro Atomico Bariloche,

Aula Newton
07 Giugno 2006 ore 17.00

Tl_2Mn_2O_7 was the first compound with pyrochlore crystal structure found to exhibit Colossal Magneto Resistance (CMR). Upon entering the ferromagnetic metallic phase, a strong decrease of resistivity is observed at the temperature of the magnetoresistance maximum. Important differences of physical properties with the CMR Mn-perovskytes were reported, and different mechanisms for the CMR are envisaged. The paramagnetic phase of Tl_2Mn_2O_7 has been much less studied, remaining many important issues still open. In this work we present the first "ab initio" study of that phase, using a combined Local Density Approximation (LDA)- multiorbital Dynamical Mean Field Theory(DMFT) treatment. We calculate the electronic structure and show how, through the inclusion of the Mn intra- and inter-orbital local correlations, the system evolves from the LDA-predicted metal to an insulator, by opening a gap at the Fermi level. This coincides with optical conductivity measurements, whose low-energy features we can fit remarkably well. We also compare our results with recent photoemission data, as well as with effective model predictions.