Enantiosensitive molecular compass

Abstract

Chirality describes the asymmetry between an object and its mirror image and underlies diverse functionalities across molecular, mesoscopic and bulk matter. A particularly intriguing example is chirality-induced spin selectivity (CISS), where chiral structures generate enantio-sensitive spin polarization. Despite extensive research, its microscopic origin and unexpectedly large magnitude remain unresolved. Here, we isolate the intrinsic coupling between chirality and spin by considering spin-resolved photoionization of randomly oriented chiral molecules under isotropic illumination. We show that electric-dipole photoionization in the presence of spin-orbit coupling generates intrinsic correlations between molecular orientation and photoelectron spin that survive complete isotropic averaging. We identify these spin-orientation correlations as the microscopic origin of CISS in photoionization and reveal their complementary manifestation: selecting the photoelectron spin orients the residual molecular ensemble, realizing spin-orientation locking, whereas selecting molecular orientation produces CISS. Both effects are governed by the same correlation strength, set by the magnitude of a molecular-frame photoionization Bloch vector that defines an enantio-sensitive molecular compass. An analogous compass emerges in photoexcitation. Our results establish spin - orientation correlations as a fundamental ingredient of chiral spin photodynamics and provide a microscopic framework for understanding and exploiting spin selectivity in chiral matter.