JCMS: Probing higher forms in topological matter

by Wojciech Jankowski (Cambridge University)

Monday 15 Sept 2025, 11:00 → 12:00 Europe/Stockholm

Albano 3: 6228 - Mega (22 seats) (Albano Building 3)

Abstract: String theory deals with extended objects, such as open and closed strings, which couple to the higher-form gauge fields proposed by Kalb and Ramond [1]. The flux of these tensor fields amounts to torsion in the quantum gravity contexts. I will present a construction of higher-tensorial Kalb-Ramond fields from single-particle Bloch states over momentum space, which I shall connect to physical observables in topological insulators [2]. I will show how the constructed gauge fields are equivalent to higher tensor Berry connection forms [3], dealing with the higher cohomologies of bundle gerbes, the generalisations of vector bundles. I will show that different classes of multigap phases and Hopf insulators [4] realise higher-form bundle gerbe invariants, with the corresponding higher Berry curvature fluxes being electromagnetically accessible through magnetoelectric and nonlinear optical responses. Finally, I will discuss many-body generalisations that admit fractionalisations of higher-dimensional many-body gerbe invariants.

References: [1] M. Kalb & P. Ramond, Phys. Rev. D 9, 2273 (1974). [2] W. J. Jankowski, R.-J. Slager, and G. Palumbo, arXiv:2507.22116. [3] G. Palumbo, Phys. Rev. Lett. 126, 246801 (2021). [4] W. J. Jankowski & R.-J. Slager, Phys. Rev. Lett. 133, 186601 (2024).