Enhancement and sign change of magnetic correlations in a driven quantum many-body system

• Published in: Nature (London) 2018-01, Vol.553 (7689), p.481-485
• Main Authors: Görg, Frederik, Messer, Michael, Sandholzer, Kilian, Jotzu, Gregor, Desbuquois, Rémi, Esslinger, Tilman
• Format: Article
• Language: English
• Subjects: 639/301/119/999; 639/766/36/1125; 639/766/483/3926; Antiferromagnetism; Computer simulation; Correlation; Experiments; Ferromagnetism; Gases; Hexagonal lattice; High temperature; Humanities and Social Sciences; Insulators; Irradiation; letter; Magnetism; Metal-insulator transition; multidisciplinary; Quantum theory; Science; Superconductivity; Transition temperature; Transition temperatures
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature25135

By periodically modulating the position of degenerate fermions unidirectionally in a three-dimensional optical lattice, antiferromagnetic correlations in this many-body system can be reduced, enhanced or even switched to ferromagnetic correlations. Magnetic correlations cracked Periodically driven many-body systems are versatile platforms for investigating new phases of matter, but the study of their dynamics is much more demanding than that of their static counterpart. Here, Tilman Esslinger and colleagues use a degenerate Fermi gas of ultracold potassium atoms loaded into an optical superlattice to probe the magnetic correlations in a driven fermionic many-body system. They find that antiferromagnetic correlations can be reduced, enhanced or even switched to ferromagnetic correlations. For near-resonant driving, the observed enhancement and sign reversal of the magnetic correlations can be explained with a microscopic model that features particle tunnelling and magnetic exchange energies as independently tunable parameters. Periodic driving can be used to control the properties of a many-body state coherently and to realize phases that are not accessible in static systems. For example, exposing materials to intense laser pulses makes it possible to induce metal–insulator transitions, to control magnetic order and to generate transient superconducting behaviour well above the static transition temperature 1 , 2 , 3 , 4 , 5 , 6 . However, pinning down the mechanisms underlying these phenomena is often difficult because the response of a material to irradiation is governed by complex, many-body dynamics. For static systems, extensive calculations have been performed to explain phenomena such as high-temperature superconductivity 7 . Theoretical analyses of driven many-body Hamiltonians are more challenging, but approaches have now been developed, motivated by recent observations 8 , 9 , 10 . Here we report an experimental quantum simulation in a periodically modulated hexagonal lattice and show that antiferromagnetic correlations in a fermionic many-body system can be reduced, enhanced or even switched to ferromagnetic correlations (sign reversal). We demonstrate that the description of the many-body system using an effective Floquet–Hamiltonian with a renormalized tunnelling energy remains valid in the high-frequency regime by comparing the results to measurements in an equivalent static lattice. For near-resonant driving, the enhancement and sign reversal