Nancy Sandler: "Photo-induced multiply quantized vortex states in Dirac-like materials"

Advances in stable, high-intensity light sources have opened new avenues for the dynamic control of material properties by enabling the exploration of non-perturbative modulation of charge distributions. A key development in this field is Floquet engineering, where photon-dressed bands and quasiparticle excitations exhibit unique properties absent in their parent equilibrium systems [1-2]. Landmark experiments including the observation of photon-dressed bands on surfaces of topological insulators (TIs) using time and angle-resolved photoemission spectroscopy [3-4], and the light-induced anomalous Hall effect in graphene [5]-, have established the critical role of optical parameters such as intensity, frequency, and polarization.
Moving beyond these conventional degrees of freedom, further control can be achieved by tailoring the spatial structure of optical beams, particularly through vortex light beams (VLBs). These beams possess intrinsic spin angular momentum (from circular polarization) and orbital angular momentum (due to their vorticity) [6], offering new opportunities to engineer novel driven states and pushing light-matter interactions into new regimes.
In this talk, I will present a theoretical framework for understanding the effects of irradiation of a monochromatic vortex light beam on a Dirac-like material’s surface [7]. By applying Floquet’s formalism, we derive a total angular momentum operator incorporating electron and photon fields. In contrast with previous reported results, this operator is conserved for circular polarization only, providing a formalism that allows for an exact numerical determination of Floquet quasi-energies and eigenstates. The one-photon approximation provides intuition on the nature of these states as the Hamiltonian maps to an s-wave superfluid model, revealing multiply quantized vortex states with Matricon-Caroli-de Gennes spectra. Analytic expressions derived from this mapping show remarkable agreement with numerical results. I will further contrast the emerging vortex core states with existing topological edge states and discuss their evolution as polarization shifts from circular to linear.

[1] T. Oka and S. Kitamura, “Floquet engineering of quantum materials.” Ann. Rev. Cond. Matter Phys. 10, 387–408 (2019)
[2] M. S. Rudner and N. H. Lindner, “Band structure engineering and non-equilibrium dynamics in Floquet topological insulators.” Nature Reviews Physics 2, 229–244 (2020).
[3] S. Ito, M. Schuler, M. Meierhofer, S. Schlauderer, J. Freudenstein, J. Reimann, D. Afanasiev, K. Kokh, O. Tereshchenko, J. Gudde et al., “Build-up and dephasing of Floquet–Bloch bands on subcycle timescales.” Nature 616, 696–701 (2023).
[4] F. Boschini, M. Zonno, and A. Damascelli, “Time-resolved ARPES studies of quantum materials.” Rev. Mod. Phys. 96, 015003 (2024).
[5] J. W. McIver, B. Schulte, F.-U. Stein, T. Matsuyama, G. Jotzu, G. Meier, and A. Cavalleri, “Light-induced anomalous Hall effect in graphene.” Nature Physics 16, 38–41 (2020).
[6] Y. Shen, X. Wang, Z. Xie, C. Min, X. Fu, Q. Liu, M. Gong, and X. Yuan, “Optical vortices 30 years on: OAM manipulation from topological charge to multiple singularities.” Light: Science & Applications 8, 1–29 (2019).
[7] L. I. Massaro, C. Meese, N. P. Sandler, and M. M. Asmar, “Photo-induced Multiply Quantized Vortex States in Dirac-like Materials.” Physical Review B 111, 085402 (2025).