Regensburg 2013 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 38: Correlated Electrons: Metal-Insulator Transition 1
TT 38.6: Talk
Wednesday, March 13, 2013, 10:45–11:00, H20
Importance of exchange anisotropy and superexchange for the spin-state transitions in RCoO3 (R = rare earth) cobaltates — •Guoren Zhang1, Evgeny Gorelov1, Erik Koch2,3, and Eva Pavarini1,3 — 1Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany — 2German Research School for Simulation Sciences, 52425 Jülich, Germany — 3JARA High-Performance Computing
In this work [1], we identify all relevant parameters which shift the energy balance between spin states in rare-earth cobaltates, and determine their trends. We find that the
eg-t2g crystal-field splitting increases by ∼ 250 meV when increasing pressure to 8 GPa, by about 150 meV when cooling from 1000 K to 5 K and by less than 100 meV when La is substituted with another rare earth.
Hund’s rule coupling is about the same in systems with very different spin-state transition temperature.
In addition, the Coulomb-exchange anisotropy and the super-exchange energy-gain play a crucial role.
In the LnCoO3 series (Ln=Y or R), super-exchange progressively stabilizes a low-spin ground state as the Ln3+ ionic radius decreases.
We use a simple model to describe spin-state transitions and show that, at low temperature, the formation of isolated high-spin/low-spin pairs is favored, while in the high-temperature phase, the most likely homogeneous state is high-spin, rather than intermediate spin. An orbital-selective Mott state could be a fingerprint of such a state.
[1] G. Zhang, E. Gorelov, E. Koch and E. Pavarini, Phy. Rev. B 86 184413 (2012)