Condensed Matter Seminar - Interplay Between Chirality, Charge, Spin, and Phonons in Chiral Matter

Coupling of spin and charge currents from structural chirality in non-magnetic materials, referred to as the chirality-induced spin selectivity (CISS) effect, has shown promising applications for spintronic devices at room temperature. Recent convergence of magnons, phonons, photons, and their rich interactions between spin accumulation in the chiral matters offers alternative routes to uncover the CISS effect using pure spin current theme and thermal excitation, such as the inverse CISS effect and chiral-phononactivated spin/orbital Seebeck effect. First, we will discuss the observations of the Onsager reciprocal to the CISS effect, i.e., the steady-state inverse CISS effect (ICISS) in chiral π-conjugated polymers (PII2T) [1] and ultrafast ICISS in chiral hybrid organicinorganic semiconductors (chiral-HOISs) [2]. In the steady-state ICISS response, the sign of ICISS depends on the handedness of the chiral PII2T polymer, with spin-to-charge conversion efficiency up to 0.05%. We conclude that distinct spin properties in the ICISS process are attributed to the chirality-induced spin splitting bands, as corroborated in the ultrafast ICISS response using spintronic terahertz spectroscopy. Both observations are more consistent with a spin-polarization mechanism than with a spinfiltering mechanism. We will also discuss the conversion of chiral phonons into spin and orbital angular momentum within chiral systems, such as chiral-HOIS [3] and alpha-quartz [4]. These insights aim to provide a compelling mechanistic framework for the CISS effect, a fascinating phenomenon whose underlying physical modelling remains a subject of intensive debate.