Berlin 2014 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 63: Quantum gases: Lattices III

Q 63.6: Talk

Friday, March 21, 2014, 15:15–15:30, UDL HS2002

Quantum magnetism of ultracold fermions on optical lattices with novel geometries — •Elena Gorelik and Nils Blümer — Institute of Physics, Johannes Gutenberg University, Mainz, Germany

Recently, it has become possible to tune optical lattices continuously between square and triangular geometries. We compute thermodynamics and spin correlations in the corresponding Hubbard model using determinant quantum Monte Carlo and show that the frustration effects induced by the variable hopping terms can be clearly separated from concomitant bandwidth changes by a proper rescaling of the interaction. An enhancement of the double occupancy by geometric frustration signals the destruction of nontrivial antiferromagnetic (AF) correlations at weak coupling and entropy s ln(2) (and restores Pomeranchuk cooling at strong frustration), paving the way to the long-sought experimental detection of AF in ultracold fermions on optical lattices.

Using the same method, we also explore AF signatures in other types of tunable optical lattices. We compute the double occupancy and spin correlation functions in the dimerized half-filled Hubbard model in the whole range of parameters (with lattices varying from honeycomb through simple square to isolated dimers), separate the effects of bandwidth change from the non-trivial spin-correlation physics, and determine the optimal parameters for experimental detection. Additionally, we study the impact of impurities on the AF correlations at half filling and find interesting magnetization patterns that deviate significantly from corresponding real-space DMFT predictions.