Chirality-Induced Spin Selectivity Effect in 2D Chiral Hybrid Perovskites: Chiral-Phonon-Activated Spin Seebeck Effect

The Chirality-Induced Spin Selectivity (CISS) effect, a unique ‘spin filtering’ effect arising from the structural handedness of organic compounds (i.e., chirality) and their assemblies that lack inversion symmetry [1]. It utilizes chirality to generate robust spin information from chiral (left- (S) or right-handed (R)) molecules without the need for common magnetic elements. The CISS effect provides a strong coupling between spin and electronic properties without the need for magnetic ordering. Recently, the CISS effect has been reported in 2D chiral hybrid perovskites (2D-chiral-HOIPs), a resurgent class of solution-processed hybrid semiconductors consisting of alternating layers of chiral organic compounds and inorganic framework of corner-sharing metal halide octahedra. Although considerable progress has been made in understanding many features of the CISS response in chiral-HOPs [2,3] and other chiral materials, an adequate quantitative description of (i) the CISS effect, (ii) its strong manifestation for spin selectivity at ambient temperatures, and (iii) its mechanistic origins, is still lacking. It comes to our attentions that angular momentum in condensed matter systems, including rigid rotation and elastic deformation, can be viewed as an information vector [4]. At the microscopic scale, the lattice vibrations, i.e., phonons, can carry angular momentum and mimic the well-known information-carrying photons [5]. This phonon angular momentum, i.e., <i>chiral phonon </i>displays a non-zero phonon angular momentum when the system is displaced from equilibrium, offering a high potential for producing the CISS effect at elevated temperatures. Here we show the observation of spin currents generated by chiral phonons in a 2D chiral HOIP implanted with chiral cations when subjected to a thermal gradient [6]. The generated spin current shows a strong dependence on the chirality of the film and external magnetic fields, of which the coefficient is orders of magnitude larger than that produced by the reported spin Seebeck effect. Our findings indicate the potential of chiral phonons for spin caloritronic applications and offer a new route toward spin generation in the absence of magnetic materials. Demonstration of the chiral-phonon-activated spin Seebeck effect in 2D chiral HOIPs may aid in solving the paradoxical diversity of CISS models, shedding light on CISS-related responses observed in a wide variety of chiral systems.<br/><br/><b>References</b><br/>[1] B. Göhler <i>et al</i>. <i>Science</i> <b>331</b>, 894–897 (2011).<br/>[2] Z. Huang <i>et al</i>., <i>ACS Nano</i> <b>14</b>, 10370 (2020).<br/>[3] Y.-H. Kim, <i>et al</i>. <i>Science</i> <b>371</b>, 1129 (2021).<br/>[4] L. Zhang & N. Qiu. <i>Phys. Rev. Lett</i>. <b>115</b>, 115502 (2015).<br/>[5] H. Zhu <i>et al</i>., <i>Science,</i> <b>359</b>, 6375 (2018).<br/>[6] K. Kim <i>et al</i>., <i>Nature Materials</i> <b>22</b>, 322 (2023).