13th International Conference on the Exact Renormalization Group 2026 (ERG2026)

Functional renormalization group approach to boson-induced superconductivity in Bose-Fermi mixtures

4 Sept 2026, 14:40

20m

144 (Jubilee Building)

Talk Parallel Session

Speaker

Richard Schmidt (Institute for Theoretical Physics, Heidelberg University, Germany)

Description

In this talk I will discuss how the functional renormalization group (FRG) can be employed to study strongly interacting Bose-Fermi mixtures and, in particular, to predict and characterize mechanisms of boson-induced superconductivity. I will begin by reviewing how a self-consistent FRG framework captures the quantum phase transition from a polaronic condensate to a molecular Fermi gas observed experimentally in ultracold K-Rb mixtures [1], establishing the FRG as a reliable tool for strongly coupled Bose-Fermi systems where the interplay of competing scales precludes perturbative treatments. Building on this foundation, I will show how the strong-coupling physics of exciton-electron bound states — trions — gives rise to an emergent BCS-BEC crossover in doped atomically thin semiconductor heterostructures, where a renormalization group analysis demonstrates the relevance of beyond-Fröhlich interaction terms and predicts critical temperatures reaching up to 10% of the Fermi temperature [2]. Finally, I will present a self-consistent FRG approach to the problem of enhancing the critical temperature of an existing superconductor by coupling it to a thermal bosonic medium. Here, the mutual renormalization of fermion-fermion and boson-fermion vertices is essential: it predicts a robust enhancement of the superconducting temperature across a wide range of interactions, a nontrivial dependence on the boson mass, and a phase diagram featuring thermally induced, thermally enhanced, and BEC-induced superconductivity [3]. Throughout the talk I will emphasize how the FRG's ability to treat bosonic and fermionic fluctuations on equal footing provides physical insights that are inaccessible to conventional approaches.

References:
[1] M. Duda, X.-Y. Chen, A. Schindewolf, R. Bause, J. von Milczewski, R. Schmidt, I. Bloch, and X.-Y. Luo, Transition from a polaronic condensate to a degenerate Fermi gas of heteronuclear molecules, Nature Physics 19, 720 (2023).
[2] J. von Milczewski, X. Chen, A. Imamoglu, and R. Schmidt, Superconductivity induced by strong electron-exciton coupling in doped atomically thin semiconductor heterostructures, Phys. Rev. Lett. 133, 226903 (2024).
[3] E. Vlasiuk, M. Salmhofer, E. Demler, and R. Schmidt, Enhancing superconductivity using thermal bosons, arXiv:2603.06796 (2026).