Terahertz spin dynamics in rare-earth orthoferrites

Recent interest in developing fast spintronic devices and laser-controllable magnetic solids has sparked tremendous experimental and theoretical efforts to understand and manipulate ultrafast dynamics in materials. Studies of spin dynamics in the terahertz (THz) frequency range are particularly important for elucidating microscopic pathways toward novel device functionalities. Here, we review THz phenomena related to spin dynamics in rare-earth orthoferrites, a class of materials promising for antiferromagnetic spintronics. We expand this topic into a description of four key elements. (1) We start by describing THz spectroscopy of spin excitations for probing magnetic phase transitions in thermal equilibrium. While acoustic magnons are useful indicators of spin reorientation transitions, electromagnons that arise from dynamic magnetoelectric couplings serve as a signature of inversion-symmetry-breaking phases at low temperatures. (2) We then review the strong laser driving scenario, where the system is excited far from equilibrium and thereby subject to modifications to the free energy landscape. Microscopic pathways for ultrafast laser manipulation of magnetic order are discussed. (3) Furthermore, we review a variety of protocols to manipulate coherent THz magnons in time and space, which are useful capabilities for antiferromagnetic spintronic applications. (4) Finally, new insights on the connection between dynamic magnetic coupling in condensed matter and the Dicke superradiant phase transition in quantum optics are provided. By presenting a review on an array of THz spin phenomena occurring in a single class of materials, we hope to trigger interdisciplinary efforts that actively seek connections between subfields of spintronics, which will facilitate the invention of new protocols of active spin control and quantum phase engineering

Stability of Mixed Lead Halide Perovskite Films Encapsulated in Cyclic Olefin Copolymer at Room and Cryogenic Temperatures

Lead Mixed Halide Perovskites (LMHPs), CsPbBrI2, have attracted significant interest as promising candidates for wide bandgap absorber layers in tandem solar cells due to their relative stability and red-light emission with a bandgap ∼1.7 eV. However, these materials segregate into Br-rich and I-rich domains upon continuous illumination, affecting their optical properties and compromising the operational stability of devices. Herein, we track the microscopic processes occurring during halide segregation by using combined spectroscopic measurements at room and cryogenic temperatures. We also evaluate a passivation strategy to mitigate the halide migration of Br/I ions in the films by overcoating with cyclic olefin copolymer (COC). Our results explain the correlation between grain size, intensity dependencies, phase segregation, activation energy barrier, and their influence on photoinduced carrier lifetimes. Importantly, COC treatment increases the lifetime charge carriers in mixed halide thin films, improving efficient charge transport in perovskite solar cell applications

Assembly of Nanocatalyst As a Noninvasive Tool for Breast Cancer Diagnosis and Immunotherapy Surveillance Designed by Visually Tracking Tumor-Derived Exosomal PD-L1

Immunotherapy has reshaped the therapeutic landscape of many advanced tumors; however, its effectiveness is seriously hampered due to the limitations of existing predictors and diagnostic tools. In response, we have fabricated a noninvasive tool for the diagnosis and immunotherapy surveillance of breast cancer (BC). The diagnostic tool functions by performing dual-aptamer-activated tandem assembly of a nanocatalyst for visually tracking tumor-derived exosomal programmed death-ligand 1 (PD-L1). By accurately identifying serum exosomal PD-L1 derived from BC, the diagnostic tool can rival immunohistochemistry (IHC) in the early classification of PD-L1-positive groups, PD-L1-negative groups, and healthy donors. Furthermore, real-time monitoring of the response to immunotherapy in 6 BC patients treated with anti-PD-L1 antibodies has been successfully achieved with the naked eye or a mobile phone camera by virtue of this diagnostic tool, which is highly consistent with computed tomography. Together, our work offers an unprecedented diagnostic tool for identifying potential beneficiaries and monitoring the response to immunotherapy, which highlights the significance of exosomal PD-L1 derived from tumors as a potential tumor prognostic and diagnostic factor including but not limited to BC