New Methods for Measuring CISS
Previous research in our lab has demonstrated strong correlations between the ability of a chiral material to filter spin-polarized charge currents and the length through which the electron traverses, the chiroptical response of the material, and the type of chiral symmetry (i.e. point, planar, axial, helical etc.) of the material. In this project we are developing and using new measurement techniques to map how spin-selectivity manifests along different transport directions through a chiral material. The Figure below (top) illustrates a measurement platform for determining spin-polarized charge transport in longitudinal and transverse directions through a chiral fiber, using magnetic conductive atomic force microscopy (mcAFM). The bottom-left and bottom-middle plots show the current-voltage (I-V) response for longitudinal measurements with magnetization (B) along the +Z and -Z directions, respectively; and the plot on the bottom-right shows the I-V response with a transverse geometry for a chiral polyanaline fiber (ca 1 micron diameter and 20 micron length). When the external magnetic field direction is inverted, e.g. B(+Z) to B(-Z), the spin states of the FM electrode flip and result in the blue side of the FM electrode showing higher current than the red side of the FM electrode. These studies show that spin polarization along the fiber’s helical axis is different than that of the spin-polarization perpendicular to its helical axis and are revealing subtle features important for understanding the mechanism of CISS.
Recent publications on new CISS measurement techniques

1. Albro, J. A.; Garrett, N. T.; Govindaraj, K.; Bloom, B. P.; Rosi, N. L.; Waldeck, D. H. Measurement Platform to Probe the Mechanism of Chiral-Induced Spin Selectivity through Direction-Dependent Magnetic Conductive Atomic Force Microscopy. ACS Nano 2025, 19, 17941.
Spin Dynamics and CISS
While considerable research has explored how chiral materials affect spin-polarized charge currents, much less is known about pure spin current injection into chiral materials. In this collaborative project we are using ferromagnetic resonance (FMR) and time-resolved magneto optic Kerr effect measurements to study the dynamics of pure spin current injection into chiral materials. The image below (left) shows a schematic for FMR measurements made on chiral cobalt oxide thin films. Interestingly, a strong nonlinear dependence for the spin damping with magnetization angle was observed for chiral films, whereas the dynamics in achiral films were isotropic. These studies reveal a rich interplay between chirality and spin dynamics and offer a unique approach to direct / control spin transport.
Recent publications on spin dynamics and CISS

2. Shiby, E.; Sun, R.; Bloom, B. P.; Albro, J. A.; Sun, D.; Waldeck, D. H. Interplay between Chiroptical and Spin Transport Properties in Chiral CdSe Quantum Dot Films. Submitted.

1. Sun, R.; Wang, Z.; Bloom, B. P.; Comstock, A. H.; Yang, C.; McConnell, A.; Clever, C.; Molitoris, M.; Lamont, D.; Cheng, Z.-H.; Yuan, Z.; Zhang, W.; Hoffmann, A.; Liu, J.; Waldeck, D. H.; Sun, D. Colossal Anisotropic Absorption of Spin Currents Induced by Chirality. Sci. Adv. 2024, 10, eadn3240.​
Adsorption / Desorption properties of Chiral Molecules on Ferromagnetic Substrates
We have developed a magneto electrochemical quartz crystal microbalance (mEQCM) method to study how spin exchange interactions between chiral molecules and spin polarized surfaces can be exploited for the separation of enantiomers and to control intermolecular interactions. The image below (left) shows a schematic of the technique in which a magnetized quartz crystal is used as a working electrode to monitor the adsorption and desorption kinetics of chiral molecules at the electrode surface. The middle image shows chronoamperometry measurements at potentials for the adsorption and desorption of D-cysteine. The change in frequency response upon applied bias is used to quantify adsorption and desorption rate constants with the electrode magnetized North (red) and South (blue). An enantioselective process is observed in which the adsorption rate constant depends sensitively on the handedness and magnetization of the electrode.
Recent publications on mEQCM

5. Lu, Y.; Joy, M.; Bloom, B. P.; Waldeck, D. H. Beyond Stereoisomeric Effects: Exploring the importance of Intermolecular Electron Spin Interactions on Biorecognition. J. Phys. Chem. Lett. 2023, 14, 7032.

4. Lu, Y.; Qiu, T.; Bloom, B. P.; Subotnik, J. E.; Waldeck, D. H. Spin-Based Chiral Separations and the Importance of Molecule-Solvent Interactions. J. Phys. Chem. C 2023, 127, 14155.

3. Santra, K.; Lu, Y.; Waldeck, D. H.; Naaman, R. Spin Selectivity Damage Dependence of Adsorption of dsDNA on Ferromagnets. J. Phys. Chem. B 2023, 127, 2344.

2. Lu, Y.; Bloom, B. P.; Qian, S.; Waldeck, D. H. Enantiospecificity of Cysteine Adsorption on a Ferromagnetic Surface: Is it Kinetically or Thermodynamically Controlled? J. Phys. Chem. Lett.2021, 12, 7854.

1.Tassinari, F.; Amsallem, D.; Bloom, B. P.; Lu, Y.; Bedi, A.; Waldeck, D. H.; Gidron, O.; Naaman, R. Spin-dependent Enantioselective Electropolymerization. J. Phys. Chem. C 2020, 124, 20974.