Päivi Törmä: Quantum geometry, superfluidity and superconductivity in flat bands and moiré superlattices
Abstract
Quantum geometry, namely quantities such as quantum metric, Berry curvature, and Chern number, have become increasingly important in understanding interacting many-body systems in solid state and ultracold gas quantum matter. We have shown that supercurrents and superfluidity in a flat band are governed by quantum geometry [1], which opens new prospects for achieving high temperature superconductivity. These findings have become relevant for superconductivity in twisted bilayer graphene and ultracold gas moiré materials [2]. We present our newest results on the topic, showing that to achieve the critical temperature enhancement, the flat band does not need to be isolated from other bands, which is promising from the experimental perspective [3]. We discuss also interesting flat band effects in the normal superconducting states could be observed [4-6]. Further, we show that quantum geometry governs the behaviour of bosonic condensates in flat bands as well, making quantum fluctuation effects remarkably strong [7].
References
[1] S. Peotta, P. Törmä, Nature Communications 6, 8944 (2015)
[2] P. Törmä, S. Peotta, B.A. Bernevig, arXiv:2111.00807, review article accepted for publication in Nat. Rev. Phys. (2022)
[3] K.-E. Huhtinen, J. Herzog-Arbeitman, A. Chew, B.A. Bernevig, P. Törmä, arXiv:2203.11133 (2022)
[4] K.-E. Huhtinen, P. Törmä, Phys. Rev. B 103, L220502 (2021)
[5] P. Kumar, S. Peotta, Y. Takasu, Y. Takahashi, P. Törmä, Phys. Rev. A 103, L031301 (2021)
[6] V.A.J. Pyykkönen, S. Peotta, P. Fabritius, J. Mohan, T. Esslinger, P. Törmä, Phys. Rev. B 103, 44519 (2021)
[7] A. Julku, G.M. Bruun, P. Törmä, Phys. Rev. Lett. 127, 170404 (2021)
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