Recently, Professor Lifa Zhang's team and foreign collaborators have made another breakthrough in the field of chiral phonons. The related research results were published in Nature Materials, a leading international journal in condensed matter physics and materials field, with the title Chiral-phonon-activated spin Seebeck effect. Nature Materials, a world-famous journal published by Nature Publishing Group, is one of the most influential journals in condensed matter physics, materials, chemistry and other disciplines, with an impact factor as high as 47.656 in 2022. Professor Lifa Zhang, Professor Jun Zhou, Professor Xiao Li and doctoral student Yu Yang undertook the theoretical calculation and numerical simulation of this paper. Professor Lifa Zhang, Professor Dali Sun and Professor Jun Liu from North Carolina State University and Professor Wei You from the University of North Carolina are co-corresponding authors of this article.

Spin is an important property of electron. By introducing this property into semiconductor devices and using electron charge and spin together as the carrier of information, spintronic devices can be realized. Compared with conventional electronic devices, spintronic devices have the characteristics of non-volatile, long lasting and high speed, which is an important direction for the development of future devices. As a way of generating pure spin flow, spin Sebeck effect has a broad application prospect in information transmission, storage, new energy development and waste heat utilization. However, the weak spin flow, the need for ferromagnetic contact and the external magnetic field greatly hinder its wide application. In this study, Prof. Lifa Zhang observed the spin current driven by chiral phonons in two-dimensional layered organic-inorganic hybrid perovskite implanted with chiral cations under the condition of non-magnetic elements (such as external magnetic field and ferromagnetic materials), and obtained a more significant spin Seebeck effect than previously reported. This is due to the introduction of chiral cations that break the spatial inversion symmetry of the material, even in the absence of an external magnetic field, the degeneration of the clockwise and counterclockwise circular-polarized phonon modes is relieved, and the non-zero angular momentum and local magnetic field under the temperature gradient can be shown to transfer or change the spin states of electrons as well as holes through electron-phonon interactions. Naturally, when the chiral cations come into contact with a thin layer of heavy metals, a strong non-equilibrium spin current similar to the spin Seebeck effect is driven in the conductor. These results indicate the potential of chiral phonons in spin thermoelectronics applications and provide new means for manipulating spin in the absence of magnetic materials. 

In this work, Professor Zhang and his collaborators observed the chiral-phonon-activated spin Seebeck effect by using ultrafast laser pulses to induce large transient temperature gradients in a non-magnetic two-dimensional chiral organic-inorganic hybrid perovskite material. By measuring the time-resolved magneto-optical Kerr effect, the transient spin current generated by chiral phonons in adjacent non-magnetic conductors is accurately detected. It is found that the phase of the chiral-phonon-activated spin current corresponds to the chiral cations of the perovskite, and can last for about 4 ns.

Link to paper: https://doi.org/10.1038/s41563-023-01473-9