Chirality induced long-range spin-selective transport in helical 3D metal-organic frameworks

The exploration of novel chiral molecules as efficient spin-filtering materials via the chirality induced spin selectivity (CISS) effect remains an active and evolving area of research within the field of chiral spintronics. Previous studies that evaluated efficient spin filtering materials primarily focused on the degree of spin polarization achieved, often overlooking critical factors such as current intensity and the range of electron conduction. In this work, we endeavoured to provide a balanced assessment of these three parameters, and consequently, we reported highly efficient spin filtering materials based on the CISS effect in three-dimensional (3D) chiral metal-organic frameworks (MOFs). A significant aspect of this work is the successful demonstration of the CISS effect in two homochiral MOF crystals, where we achieved precise control over their high degree of spin-selectivity, a long range of spin filtering (>1 µm), and substantial current intensity (∼130 nA). This is attributed to their opposite helical structures and multidimensional electron transport channels. Notably, this study provides the first demonstration of spin-selective transport in transition metal-based helical 3D MOFs. To further validate the spin-dependent transport process in chiral 3D MOFs, we developed a prototype device featuring a spin-valve configuration. Notably, the results obtained from this device correlate well with the spin-dependent processes and confirm the presence of the CISS effect in the studied MOF materials. Furthermore, we have established a direct correlation between the contact potential difference (CPD) and the chirality of the 3D MOF crystals, offering new insights into their preferential spin transport properties via the CISS effect. This correlation, largely overlooked in previous studies, represents a key advance in understanding and designing efficient CISS-based spintronic materials.