Accueil > Français > Événements > Séminaires > Séminaires Magnétisme et Supraconductivité > Archives 2012

Jan M. Tomczak - Rutgers University

Realistic Description of Correlated Materials – Iron Silicide and the Iron Pnictides

In many correlated materials deducing microscopic insights from theoretical methods is met with the difficulty that the complexity of orbitals and/or spin degrees of freedom defies a description using simple model approaches.

In the first part of my talk [1], I will illustrate the promising prospect of “realistic" many-body approaches with the example of the narrow-gap semiconductor iron silicide. FeSi exhibits an unusual metalization process which is poorly understood : at low temperatures
FeSi behaves as an ordinary semi-conductor, while at high temperatures the system is a bad metal with a Curie-like susceptibility. While several explanations for this behaviour were
proposed, a consensus remained elusive, owing to the lack of quantitative methodologies. We use realistic dynamical mean field theory (DMFT) calculations to elucidate the metalization
mechanism of FeSi. Our methodology accounts for all major anomalies observed in FeSi, e.g., spectral weight transfers in the optical conductivity, the Curie susceptibility and an anomalous thermoelectric power. Having quantitatively validated our method for this system,
we propose a new scenario for the underlying physics of FeSi. The DMFT framework employed for FeSi accounts for short-range electronic correlation effects only.

In the second part of my talk [2], I will argue that for the iron pnictides and chalcogenides the ad hoc assumption of non-local correlation effects being negligible is not fully warranted. I will, however, demonstrate that non-local effects are static in nature, and I
will propose a scheme that includes these effects in the DMFT framework.


[1] JMT, K. Haule, and G. Kotliar, PNAS 109, 3243 (2012)

[2] JMT, M. van Schilfgaarde, and G. Kotliar, PRL (in press), arXiv:1209.2213


C.J. van der Beek - X 01 69 33 40 90(

Y. Sidis - LLB 01 69 08 96 85 (

V. Brouet – LPS (coordinatrice) 01 69 15 53 34 (

F. Rullier Albenque - SPEC 01 69 08 75 48 (