DigiQ talk from Professor Päivi Törmä

This DigiQ talk features Aalto University Professor Päivi Törmä. The title of her talk is "Quantum geometry in flat band superconductivity, Bose-Einstein condensation and light-matter interactions."

Event details

When: 14:00-15:00, 19.6.2024
Where: Tietotekniikka, Hall C105 T2, Konemiehentie 2, Otaniemi
Register: Webropol link to register

From Päivi: What will your talk discuss?

We have found that superconductivity and superfluidity have a connection to quantum geometry [1,2]. Namely, the superfluid weight in a multiband system has a previously unnoticed component which we call the geometric contribution. It is proportional to the minimal quantum metric of the band. Quantum metric is connected to the Berry curvature, and this allows to relate superconductivity with the topological properties of the band. Using this theory, we have shown that superconductivity is possible also in a flat band where individual electrons would not move. We and other groups have shown [3,4] that these results may be essential in explaining the observation of superconductivity in twisted bilayer graphene and may eventually help realize superconductors at elevated temperatures. In addition to the promise of high critical temperatures and strong correlation effects, also the quantum transport in flat band shows unique behavior [5]: while supercurrent can flow, quasiparticle transport is highly suppressed even in non-equilibrium conditions. This may have important consequences for superconducting devices. We have found that quantum geometry also governs Bose-Einstein condensates in flat bands [6] and light-matter interactions [7]. We have also experimentally observed the quantum metric and non-Hermitian Berry curvature in plasmonic lattices [8,9].

[1] S. Peotta, P. Törmä, Nature Commun. 6, 8944 (2015); A. Julku, S. Peotta, T.I. Vanhala, D.-H. Kim, P. Törmä, Phys. Rev. Lett. 117, 045303 (2016); P. Törmä, L. Liang, S. Peotta, Phys. Rev. B 98, 220511(R) (2018).
[2] K.-E. Huhtinen, J. Herzog-Arbeitman, A. Chew, B.A. Bernevig, P. Törmä, Phys. Rev. B 106 , 014518 (2022); J. Herzog-Arbeitman, A. Chew, K.-E. Huhtinen, P. Törmä, B.A. Bernevig, arXiv:2209.00007 (2022).
[3] A. Julku, T.J. Peltonen, L. Liang, T.T. Heikkilä, P. Törmä, Phys. Rev. B 101, 060505(R) (2020); X. Hu, T. Hyart, D.I. Pikulin, E. Rossi, Phys. Rev. Lett. 123, 237002 (2019); F. Xie, Z. Song, B. Lian, B.A. Bernevig, Phys. Rev. Lett. 124, 167002 (2020).
[4] P. Törmä, S. Peotta, B.A. Bernevig, Nat. Rev. Phys. 4, 528 (2022).
[5] V.A.J. Pyykkönen, S. Peotta, P. Törmä, Phys. Rev. Lett. 130, 216003 (2023).
[6] A. Julku, G.M. Bruun, P. Törmä, Phys. Rev. Lett., 127, 170404 (2021), ibid Phys. Rev. B 104, 144507 (2021)
[7] G.E. Topp, C.J. Eckhardt, D.M. Kennes, M.A. Sentef, P. Törmä, Phys. Rev. B 104, 064306 (2021)
[8] J. Cuerda, J.M. Taskinen, N. Källman, L. Grabitz, P. Törmä, Phys. Rev. Reseach 6, L022020 (2024)
[9] J. Cuerda, J.M. Taskinen, N. Källman, L. Grabitz, P. Törmä, Phys. Rev. B 109, 165439 (2024)