Hamburg 2009 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 22: Quantengase: Fermionen im Gitter

Q 22.3: Vortrag

Dienstag, 3. März 2009, 14:45–15:00, VMP 6 HS-A

A Mott insulator of ultracold fermions in an optical lattice — •Robert Jördens, Niels Strohmaier, Daniel Greif, Leticia Tarruell, Henning Moritz, and Tilman Esslinger — Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland

Strong interactions between electrons in a solid material lead to surprising effects such as the Mott insulator, where a suppression of conductivity occurs due to interactions rather than due to a filled Bloch band. Proximity to the Mott insulating phase is the origin of many intriguing phenomena in condensed matter physics, most notably high-temperature superconductivity.

We implement the Fermi-Hubbard model, which encompasses the physics of the Mott insulator, by trapping a repulsively interacting two-component Fermi gas in an optical lattice. In agreement with theoretical models, the double occupancy provides a versatile and sensitive probe to the system’s properties and signals the formation of a Mott insulator by three features: a drastic suppression of doubly occupied lattice sites, a strong reduction of the compressibility, and the appearance of an excitation mode corresponding to the creation of double occupancies. In the regime of strong interactions, this mode establishes a direct measurement of the Hubbard U and allows us to study the process of creation and decay of double occupancies.