Speaker: Dr. Mark Dean(BNL)

Host: Yao Wang 

Title: Exploring many-body excitons with resonant inelastic X‑ray scattering

Abstract: Excitons—correlated electron–hole pairs—play a central role in the optical and electronic properties of solids. In quantum materials, strong electronic correlations and exchange interactions can produce unconventional many-body excitons whose momentum dependence, symmetry, and coupling to magnetism remain poorly understood. In this talk, I will show how resonant inelastic X-ray scattering (RIXS) [1], with its combined sensitivity to energy, momentum, and excitation symmetry, provides a powerful view of these states. I will discuss magnetically propagating Hund’s excitons in NiPS3 [2], dispersive dark excitons in CrI3 [3], and anisotropic excitonic states in CrSBr [4]. Together, these results illustrate how excitons can encode and transmit the intertwined spin, orbital, and charge character of quantum materials. I will conclude with an outlook on using ultrafast pump–probe RIXS to create and track such states away from equilibrium.

Bio: I am the X-ray Scattering Group Leader at Brookhaven and run a research program that focuses on resonant inelastic X-ray scattering (RIXS) of quantum materials. My research interests include complex oxides, strongly spin–orbit-coupled materials, quantum heterostructures, non-equilibrium states, and topology in crystalline materials. I earned my PhD from the University of Cambridge in 2010. My work has been recognized with a Department of Energy Early Career Award in 2014 and the Distinction of Tenure from Brookhaven in 2022, and I currently serve on the editorial board of Physical Review X.