Fyzikální ústav Akademie věd ČR

Seminář Úterý, 29. červen 2010 - 15:00 - 16:00

Přednášející: Karsten Held (Institute for Solid State Physics, TU Wien)
Místo: Na Slovance, přednáškový sál v přízemí
Pořadatelé: Oddělení teorie kondenzovaných látek
Jazyk přednášky: angličtina

Abstract
Despite being the prototype for strongly correlated electron systems, an accurate calculation of the critical behavior of the Hubbard model was hitherto not possible. With the recently developed dynamical vertex approximation (DΓA) [1], we are finally able to include non-local correlations beyond dynamical mean field theory (DMFT) in a systematic way - on all length scales. In two dimensions, this results in a reduction of the antiferromagnetic transition temperature to T_N=0, in agreement with the Mermin-Wagner theorem. In three dimensions, we get a non-mean-field critical behavior, in contrast to DMFT. It approximately agrees, at least for half filling and large Coulomb repulsion, with the Heisenberg critical exponents. By means of DΓA, we are also able to estimate the error of DMFT. In particular, we will discuss in which regions of the phase diagram a DMFT treatment is sufficient and where non-local correlations necessarily need to be included. Besides, DΓA is also promising to apply to nanoscopic systems [2].

[1] A. Toschi, A. A. Katanin, K. Held, Phys. Rev. B 75, 045118 (2007); Phys. Rev. B 80, 075104 (2009).
[2] A. Valli et al., Phys. Rev. Lett. 104, 246402 (2010).

Přílohy

presentation (pdf)

voice record (mp3)