"Ab-initio (LDA+DMFT) description of CMR pyrochlore Tl2Mn2O7"
Relatore: Dr. Cecilia I. Ventura, Centro Atomico Bariloche,
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.