Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 25: Focussed session: Frontiers of electronic structure theory: Strong correlations from first principles II (jointly with TT)

O 25.3: Vortrag

Dienstag, 27. März 2012, 11:15–11:30, HE 101

Iron under extreme conditions: the impact of electronic correlations — •Leonid Pourovskii — CPHT-Ecole Polytechnique, Palaiseau, France — IFM, Linköping university, Linköping, Sweden

We have applied a fully self-consistent full-potential ab initio dynamical mean-filed theory approach to study the impact of electronic correlations on electronic, elastic, and magnetic properties of iron at both moderate and high pressures and temperatures. Our simulations have established the existence of an electronic topological transition in the hcp phase of iron at pressures of about 30-40 GPa, with new hole pockets appearing in the Fermi surface with decreasing volume and leading to anomalies in the Debye sound velocity, lattice parameters c/a ratio and Mössbauer central shift. These anomalies are indeed observed in our experiments. With our calculations extended to pressures and temperatures expected for the Earth deep core we find that the fcc and hcp phases remain in the Fermi liquid regime, while the bcc phase is an incoherent *bad* metal as evidenced by a significant non-Fermi liquid life-time broadening of low-energy electronic states and a large entropic contribution to the electronic free energy. Our calculations also suggest that all three likely crystal structure of iron and iron-rich alloys in the Earth inner core, the hcp, the face centered cubic (fcc), and the body centered cubic (bcc), have sufficiently high magnetic susceptibility to stabilize the geodynamo. The strongest effect is predicted for the bcc Fe, which at the Earth core conditions is still characterized by a Curie-Weiss behavior of the magnetic susceptibility corresponding to a local magnetic moment 1.5 Bohr magnetons.