dd2D

This project is dedicated to uncovering the ultrafast behavior of d–d transitions — local orbital excitations characteristic of correlated transition-metal compounds. In two-dimensional van der Waals antiferromagnets, such excitations provide a unique window into strong electronic correlations and their coupling to other degrees of freedom.

Our approach relies on time- and angle-resolved photoemission (trARPES), which allows us to follow the buildup and decay of d–d transitions with femtosecond time resolution and full momentum sensitivity.

First insights, obtained in FePS₃ (Newton, 2025), revealed how d–d excitations emerge within 100 fs and decay on picosecond timescales, disentangling different excitation pathways. Building on this foundation, the project aims to establish a microscopic understanding of d–d excitations in 2D correlated materials and their potential for controlling quantum matter.

Our recent results in CrPS₄ provide a microscopic explanation for the pronounced optical activity of such transitions. ARPES measurements combined with first-principles calculations reveal an orbital-selective electronic structure: weakly hybridized, correlation-sensitive t₂_g states stabilize local magnetism, whereas strongly hybridized e_g–ligand states govern the optical response. This hybridization relaxes the selection rules that would otherwise suppress d–d transitions, thereby making them optically accessible.