Strong pairing in mixed-dimensional bilayer antiferromagnetic Mott insulators

Abstract

Interacting many-body systems in reduced-dimensional settings, such as ladders and few-layer systems, are characterized by enhanced quantum fluctuations. Recently, two-dimensional bilayer systems have sparked considerable interest because they can host unusual phases, including unconventional superconductivity. Here we present a theoretical proposal for realizing high-temperature pairing of fermions in a class of bilayer Hubbard models. We introduce a general and highly efficient pairing mechanism for mobile charge carriers in doped antiferromagnetic Mott insulators. The pairing is caused by the energy that one charge gains when it follows the path created by another charge. We show that this mechanism leads to the formation of highly mobile but tightly bound pairs in the case of mixed-dimensional Fermi–Hubbard bilayer systems. This setting is closely related to the Fermi–Hubbard model believed to capture the physics of copper oxides, and can be realized in currently available ultracold atom experiments.

Solving 2D and 3D lattice models of correlated fermions -- combining matrix product states with mean field theory

“…Such a regime is realized for instance in the various insulating phases of the Bechgaard and Fabre salts [21,22]. Alternatively, such regimes may be found, with minor modifications, in the recently proposed and partially realized mixed-dimensional large-J systems in ultracold fermionic lattice gases [23,24]. At the same time, the quantitative study of USC regimes of the same compounds, as well as of other Q1D materials such as Chromium pnictide [25,26] and the telephonenumber compounds [27,28], would require including single-electron tunneling in-between 1D sub-units.…”

Magnetically mediated hole pairing in fermionic ladders of ultracold atoms

“…The key motivation for our work was to provide an experimental realization of this system that has been considered only a theoretical abstraction. We achieve this by extending Fermi–Hubbard ladders at large interactions with a potential offset, effectively realizing a mixed-dimensional (mixD) system 10 .…”

“…The strong rung coupling keeps the spatial extent of hole pairs small while staying in the regime in which spin correlations and hole motion compete on a comparable energy scale. For larger t ∥ , the binding energy is even expected to grow 10 but becomes harder to observe in systems of limited sizes because of increased pair sizes.…”

“…This repulsion between pairs is an indication of the comparably high mobility of pairs in mixD settings, which could be further enhanced by increasing the leg tunnelling t ∥ in larger systems. Such highly mobile pairs can potentially reach very high critical temperatures 10 and can be an important ingredient for high- T C superconductivity.

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“…Here we experimentally observe this long-standing theoretical prediction, reporting hole pairing due to magnetic correlations in a quantum gas of ultracold atoms. By engineering doped antiferromagnetic ladders with mixed-dimensional couplings 10 , we suppress Pauli blocking of holes at short length scales. This results in a marked increase in binding energy and decrease in pair size, enabling us to observe pairs of holes predominantly occupying the same rung of the ladder.…”