Enantiospecific Magnetoconductance Asymmetry in a Racemic Conglomerate Driven by Surface-Assisted Symmetry Breaking

Chirality-induced spin selectivity (CISS) has been predominantly demonstrated in enantiopure systems, while racemic mixtures are considered spin-inactive due to the cancellation of opposite enantiomeric contributions. Here, we demonstrate that surface-assisted symmetry breaking activates CISS in racemic systems. A racemic bis-helical [1]benzothieno[3,2-b]benzothiophene (BTBT) derivative (Rac-1) spontaneously segregates into homochiral (M,M) and (P,P) domains, forming a two-dimensional (2D) racemic conglomerate directly visualized by scanning tunneling microscopy (STM). Scanning tunneling spectroscopy (STS) reveals enantiospecific magnetoconductance asymmetry (EMA) within individual homochiral domains at room temperature, reaching +(40 ± 5)% for (P,P) domains and -(35 ± 10)% for (M,M) domains when the ferromagnetic Co layer is magnetized perpendicular to the substrate plane. Magnetization-direction-dependent STS measurements show that EMA is reduced from ∼35% for out-of-plane to <6% for in-plane Co layer orientation. Distance-dependent STS and control measurements on Au(111)/Mica without a ferromagnetic layer further confirm that EMA is intrinsic to CISS and independent of junction artifacts. Despite surface-induced planarization of the molecular backbone upon adsorption, as revealed by DFT calculations, EMA persists, driven by the collective 2D chiral packing and the resulting chiral electrostatic potential at the molecule-surface interface. These results establish that bulk homochirality is not a prerequisite for room-temperature CISS, identifying racemic conglomerates as a synthetically accessible platform for investigating CISS at the nanoscale.