The TRR 227 kindly invites you to the joint Colloquium of the TRR 227 & FU Physics Department.

Speaker: Prof. Dr. Olga Smirnova, 
Max-Born-Institut für Nichtlineare Optik u. Kurzzeitspektroskopie & TU Berlin

Title: Chirality in time: from topology of temporal shapes to spin selectivity in chiral molecules

Abstract:

Chirality—the property that distinguishes left- and right-handed forms of matter—underpins diverse functionalities across scales, from molecules that come in two non-superimposable mirror-image forms known as enantiomers to chiral materials and photonic structures. Yet fast, sensitive, and robust chiral optical detection remains a major challenge because conventional chiroptical spectroscopies access chirality only through weak corrections to the dominant electric-dipole interaction. Here, we introduce temporal chirality—chirality encoded in the time-dependent trajectories traced by vectors such as electric fields or induced polarizations—as a unifying framework that reveals highly efficient enantio-sensitive observables that employ the strongest, electric-dipole way of light–matter coupling [1].

Synthetic chiral light [2] provides a central example: the Lissajous figure traced by its electric-field vector forms a locally chiral three-dimensional trajectory in time. Correlating local chirality across both time and azimuthal space one can enable chiral topological light [3]. We show that such light enables topologically robust enantio-sensitive signals. We further demonstrate that synthetic chiral light can be efficiently guided in an optical fibers, enabling enantio-sensitive harmonic emission from very small quantities of chiral molecules and opening pathways to compact microfluidic platforms for rapid chiral analysis.

Light-induced polarization in excited chiral molecules can also exhibit temporal chirality, generating geometric fields that influence photoelectron spin and give rise to new mechanisms of spin–chirality coupling [4,5,6]. We find that any excited or photoionized chiral molecule can act as an enantio-sensitive molecular compass [4], defining an internal geometric axis even under isotropic illumination. Just as a traditional compass needle aligns with Earth’s magnetic field, the molecular compass aligns the electron spin with a built-in geometric direction inside the molecule — a direction defined by its handedness. In this way, the molecule generates its own “chiral north,” guiding the electron spin without any magnetic interaction. A complementary Berry-curvature-driven spin torque, activated by photon spin, produces a triple lock between molecular structure, photon spin, and electron spin—providing a geometric and topological foundation for the chirality-induced spin-selectivity (CISS) effect.

[1] O. Smirnova, Science 389, 232 (2025).
[2] D. Ayuso et al, Nature Photonics 13, 866 (2024).
[3] N. Mayer et al, Nature Photonics 18, 1155 (2024).
[4] P. C. M. Flores et al, arXiv: 2505.22433.
[5] P. C. M. Flores et al, arXiv:2603.02735.
[6] P. C. M. Flores et al, arXiv:2505.23460.