A Microscopic View of Fermionic Mott-Insulators
Conventional band theory predicts an insulating behavior of a solid if the freely moving electrons occupy every possible quantum state in the highest energy band, whereas the state is conducing otherwise. This simple picture is altered in the presence of strong interactions, which can lead to an insulating behavior even in the presence of a half-filled energy band. These Mott-insulators, named after the British physicist Sir Nevill F. Mott, are one of the conceptually simplest examples of many-body systems, where strong correlations lead to surprising phenomena.
Researchers at Harvard have now synthesized and studied such Mott-insulators with high-resolution microscopy by cooling Li-6 atoms to extremely low temperatures below 50 nK, deep in the quantum degenerate regime, and trapping them into a crystalline structure formed by intersecting laser beams. This synthetic version of a solid by means of an optical lattice gives the researchers an exceptional tunability and control over the system, for example the strength of the interactions. By combining this approach with a novel imaging technique developed for neutral fermionic atoms, the team around Prof. Markus Greiner at Harvard University was able to image the atomic distribution of the Mott-insulating state with single site and single atom resolution.
The researchers’ results demonstrate that combining ultracold fermions in optical lattices and quantum gas microscopy could allow shedding new light into complex states of quantum matter in the future, where even the most sophisticated theoretical methods cannot provide a reliable prediction. Examples range from high-temperature superconductors, which is believed to occur in the proximity of an antiferromagnetic Mott-insulator, to frustrated quantum magnets, which show an intriguing interplay between the lattice geometry and the magnetic ordering. In addition, quantum gas microscopy even allows creating arbitrary potential landscapes for the ultracold atoms. This opens entirely new perspectives for studying and probing quantum many-body systems at the site-resolved level.
To read more see D. Greif et al., Science 351, 953 (2016)
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