Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 10: Correlated Electrons: (General) Theory 1
TT 10.9: Vortrag
Montag, 26. März 2012, 17:15–17:30, H 3010
Momentum-dependent pseudogaps in the half-filled 2d Hubbard model — •Daniel Rost1, Elena Gorelik1, Fakher Assaad2, and Nils Blümer1 — 1Institute of Physics, Johannes Gutenberg-University, Mainz, Germany — 2Institute of Theoretical Physics and Astrophysics, University of Würzburg, Germany
A peculiar feature of (underdoped) high-Tc superconductors is the occurrence of pseudogaps in the normal state, i.e. a suppression of the density of states at the Fermi energy. It has been unclear for a long time whether and in which parameter regimes this phenomenon is captured by the two-dimensional Hubbard model: spectra obtained from determinantal quantum Monte Carlo (DQMC) simulations suffer from large finite-size (as well as Trotter and statistical) errors; partial conclusions for the thermodynamic limit were only possible by complementing DQMC data with cluster extensions of the dynamical mean-field theory (DMFT) and with the dynamical vertex approximation.
We present a method for extrapolating DQMC Green functions to the limit of infinite cluster size L→∞ and vanishing Trotter discretization Δτ→0. Thus, we obtain, via the maximum entropy method, the first unbiased spectra in the thermodynamic limit. Our results establish that a pseudogap opens in the 2d Hubbard model at weak coupling below a characteristic temperature Tpg which (for U=4t) agrees with DMFT Néel temperature. It opens first at ka=(π,0), i.e. shows d wave type anisotropy at T≲ Tpg even at half filling; this momentum dependence (an effect not captured by DMFT) decays towards larger interactions.