Letter abstract
Nature Physics 4, 617 - 621 (2008)
Published online: 30 May 2008 | doi:10.1038/nphys983
Subject Categories: Condensed-matter physics | Atomic and molecular physics | Optical physics
Sharp peaks in the momentum distribution of bosons in optical lattices in the normal state
Yasuyuki Kato1, Qi Zhou2, Naoki Kawashima1 & Nandini Trivedi2
Cold atoms in optical lattices provide a unique laboratory for investigating quantum phase transitions between strongly correlated superfluid and Mott insulator phases1, 2. One of the major bottlenecks in the analysis of experiments is a clear set of criteria for identifying the superfluid phase3. A 'sharp' interference pattern in time-of-flight experiments has been widely adopted as a signature of superfluidity4, 5, 6, 7, 8. Here, we show that sharp peaks are not a reliable diagnostic of superfluidity. Using large-scale quantum Monte Carlo simulations of the Bose–Hubbard model in three dimensions with up to N=1.4
104 particles, we calculate the momentum distribution n(k) as a function of temperature T and t/U, the ratio of hopping to the onsite repulsion. We find that even above the transition temperature Tc where both superfluid density and condensate fraction vanish, the interference pattern can nevertheless have sharp peaks riding over a broad background. We identify the true signature of the superfluid and give a deeper understanding of why such sharp peaks appear in the normal state.
- Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8581, Japan
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
Correspondence to: Nandini Trivedi2 e-mail: trivedi.15@osu.edu
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