Presented by: Matthew C. Beard, National Laboratory of the Rockies

Abstract: The interplay between spin and charge in chiral materials — ranging from simple organic molecules to complex hybrid semiconductors — has emerged as one of the more intriguing open scientific problems. Chirality is fundamentally a symmetry question — an object is chiral if it cannot be superimposed on its mirror image — and chirality-induced spin selectivity (CISS), whereby chiral materials preferentially transmit electrons of a particular spin orientation, is a striking consequence of this broken symmetry. This observation has proven controversial, as large spin polarization from organic molecules challenges conventional wisdom about the requirements for spin-selective transport. The underlying symmetry constraint is elegant: reversing the structural handedness or the electron spin independently produces measurably different outcomes, while reversing both simultaneously leaves observables unchanged. Yet translating these symmetry constraints into a complete microscopic theory has remained challenging despite two decades of robust experimental evidence. We have developed a new class of chiral organic-inorganic hybrid semiconductors in which chiral molecules imbue chirality into an inorganic semiconductor framework. Using this platform, I will present experimental demonstrations of both CISS and Inverse-CISS and show how the observed symmetry behavior places meaningful constraints on theory. These constraints point toward a natural resolution in which spin and spatial degrees of freedom in chiral materials are fundamentally non-separable, giving rise to spin-displacement order with no analog in achiral systems.

Host: Markus Raschke