Observation of a pairing pseudogap in a two-dimensional Fermi gas

• Published in: Nature (London) Vol. 480; no. 7375; pp. 75 - 78
• Main Authors: Feld, Michael, Fröhlich, Bernd, Vogt, Enrico, Koschorreck, Marco, Köhl, Michael
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2011; Nature Publishing Group
• Subjects: 639/638/298/924; 639/766/119; 639/766/419; Atoms & subatomic particles; Exact sciences and technology; Experiments; Humanities and Social Sciences; letter; multidisciplinary; Physics; Science; Spectrum analysis; Studies; Temperature; The physics of elementary particles and fields; Transition temperatures; Spectroscopy; Ultracold gas; Superconductors; Transition temperature; Fermi gas; Fermions; Superfluid; Superconductivity; Strong coupling; Spectral functions; Superfluidity; Pairing
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10627

Observation of a many-body pairing gap in a trapped, 2D atomic Fermi gas shows that ultracold atomic gases can be used to emulate the physics of correlated 2D superconductors, with the ultimate goal of understanding high-temperature superconductivity. Pairing pseudogap in a two-dimensional Fermi gas Michael Köhl and colleagues report the observation of a pseudogap — a phenomenon that precedes superfluid fermionic pairing in an ultracold, two-dimensional atomic quantum gas. The gap appears above the superfluid transition temperature and is detected through momentum-resolved photoemission spectroscopy. The results demonstrate that ultracold atomic gases can be used to emulate the physics of correlated two-dimensional superconductors, with the ultimate goal of understanding high-temperature superconductivity. Pairing of fermions is ubiquitous in nature, underlying many phenomena. Examples include superconductivity, superfluidity of 3 He, the anomalous rotation of neutron stars, and the crossover between Bose–Einstein condensation of dimers and the BCS (Bardeen, Cooper and Schrieffer) regime in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems show even more subtle effects 1 , many of which are not understood at a fundamental level. Most striking is the (as yet unexplained) phenomenon of high-temperature superconductivity in copper oxides, which is intimately related to the two-dimensional geometry of the crystal structure. In particular, it is not understood how the many-body pairing is established at high temperature, and whether it precedes superconductivity. Here we report the observation of a many-body pairing gap above the superfluid transition temperature in a harmonically trapped, two-dimensional atomic Fermi gas in the regime of strong coupling. Our measurements of the spectral function of the gas are performed using momentum-resolved photoemission spectroscopy 2 , 3 , analogous to angle-resolved photoemission spectroscopy in the solid state 4 . Our observations mark a significant step in the emulation of layered two-dimensional strongly correlated superconductors using ultracold atomic gases.