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1. Organic-to-inorganic structural chirality transfer in a 2D hybrid perovskite and impact on Rashba-Dresselhaus spin-orbit coupling

   https://doi.org/10.1038/s41467-020-18485-7  

   Jana, Manoj K. ; Song, Ruyi ; Liu, Haoliang ; Khanal, Dipak Raj ; Janke, Svenja M. ; Zhao, Rundong ; Liu, Chi ; Valy Vardeny, Z. ; Blum, Volker ; Mitzi, David B. ( September 2020 , Nature Communications)

   Translation of chirality and asymmetry across structural motifs and length scales plays a fundamental role in nature, enabling unique functionalities in contexts ranging from biological systems to synthetic materials. Here, we introduce a structural chirality transfer across the organic–inorganic interface in two-dimensional hybrid perovskites using appropriate chiral organic cations. The preferred molecular configuration of the chiral spacer cations,R-(+)- orS-(−)-1-(1-naphthyl)ethylammonium and their asymmetric hydrogen-bonding interactions with lead bromide-based layers cause symmetry-breaking helical distortions in the inorganic layers, otherwise absent when employing a racemic mixture of organic spacers. First-principles modeling predicts a substantial bulk Rashba-Dresselhaus spin-splitting in the inorganic-derived conduction band with opposite spin textures betweenR- andS-hybrids due to the broken inversion symmetry and strong spin-orbit coupling. The ability to break symmetry using chirality transfer from one structural unit to another provides a synthetic design paradigm for emergent properties, including Rashba-Dresselhaus spin-polarization for hybrid perovskite spintronics and related applications.
2. Topological spin/structure couplings in layered chiral magnet Cr _1/3 TaS ₂ : The discovery of spiral magnetic superstructure

   https://doi.org/10.1073/pnas.2023337118  

   Du, Kai ; Huang, Fei-Ting ; Kim, Jaewook ; Lim, Seong Joon ; Gamage, Kasun ; Yang, Junjie ; Mostovoy, Maxim ; Garlow, Joseph ; Han, Myung-Geun ; Zhu, Yimei ; et al ( September 2021 , Proceedings of the National Academy of Sciences)

   Chiral magnets have recently emerged as hosts for topological spin textures and related transport phenomena, which can find use in next-generation spintronic devices. The coupling between structural chirality and noncollinear magnetism is crucial for the stabilization of complex spin structures such as magnetic skyrmions. Most studies have been focused on the physical properties in homochiral states favored by crystal growth and the absence of long-ranged interactions between domains of opposite chirality. Therefore, effects of the high density of chiral domains and domain boundaries on magnetic states have been rarely explored so far. Herein, we report layered heterochiral Cr_1/3TaS₂, exhibiting numerous chiral domains forming topological defects and a nanometer-scale helimagnetic order interlocked with the structural chirality. Tuning the chiral domain density, we discovered a macroscopic topological magnetic texture inside each chiral domain that has an appearance of a spiral magnetic superstructure composed of quasiperiodic Néel domain walls. The spirality of this object can have either sign and is decoupled from the structural chirality. In weak, in-plane magnetic fields, it transforms into a nonspiral array of concentric ring domains. Numerical simulations suggest that this magnetic superstructure is stabilized by strains in the heterochiral state favoring noncollinear spins. Our results unveil topological structure/spinmore »couplings in a wide range of different length scales and highly tunable spin textures in heterochiral magnets.

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3. Chiral-phonon-activated spin Seebeck effect

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

   Kim, Kyunghoon ; Vetter, Eric ; Yan, Liang ; Yang, Cong ; Wang, Ziqi ; Sun, Rui ; Yang, Yu ; Comstock, Andrew H. ; Li, Xiao ; Zhou, Jun ; et al ( February 2023 , Nature Materials)

   Utilization of the interaction between spin and heat currents is the central focus of the field of spin caloritronics. Chiral phonons possessing angular momentum arising from the broken symmetry of a non-magnetic material create the potential for generating spin currents at room temperature in response to a thermal gradient, precluding the need for a ferromagnetic contact. Here we show the observation of spin currents generated by chiral phonons in a two-dimensional layered hybrid organic–inorganic perovskite implanted with chiral cations when subjected to a thermal gradient. 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 towards spin generation in the absence of magnetic materials.
4. Polar coupling enabled nonlinear optical filtering at MoS2/ferroelectric heterointerfaces

   https://doi.org/10.1038/s41467-020-15191-2  

   Li, Dawei ; Huang, Xi ; Xiao, Zhiyong ; Chen, Hanying ; Zhang, Le ; Hao, Yifei ; Song, Jingfeng ; Shao, Ding-Fu ; Tsymbal, Evgeny Y. ; Lu, Yongfeng ; et al ( March 2020 , Nature Communications)

   Complex oxide heterointerfaces and van der Waals heterostructures present two versatile but intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS₂and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.
5. Strengthened relaxor behavior in (1− x )Pb(Fe _0.5 Nb _0.5 )O ₃ – x BiFeO ₃

   https://doi.org/10.1039/C9TC05883D  

   Prah, Uroš ; Dragomir, Mirela ; Rojac, Tadej ; Benčan, Andreja ; Broughton, Rachel ; Chung, Ching-Chang ; Jones, Jacob L. ; Sherbondy, Rachel ; Brennecka, Geoff ; Uršič, Hana ( March 2020 , Journal of Materials Chemistry C)

   A systematic study of (1− x )Pb(Fe 0.5 Nb 0.5 )O 3 – x BiFeO 3 ( x = 0–0.5) was performed by combining dielectric and electromechanical measurements with structural and microstructural characterization in order to investigate the strengthening of the relaxor properties when adding BiFeO 3 into Pb(Fe 0.5 Nb 0.5 )O 3 and forming a solid solution. Pb(Fe 0.5 Nb 0.5 )O 3 crystalizes in monoclinic symmetry exhibiting ferroelectric-like polarization versus electric field ( P–E ) hysteresis loop and sub-micron-sized ferroelectric domains. Adding BiFeO 3 to Pb(Fe 0.5 Nb 0.5 )O 3 favors a pseudocubic phase and a gradual strengthening of the relaxor behavior of the prepared ceramics. This is indicated by a broadening of the peak in temperature-dependent permittivity, narrowing of P–E hysteresis loops and decreasing size of ferroelectric domains resulting in polar nanodomains for x = 0.20 composition. The relaxor behavior was additionally confirmed by Vogel–Fulcher analysis. For the x ≥ 0.30 compositions, broad high-temperature anomalies are observed in dielectric permittivity versus temperature measurements in addition to the frequency-dispersive peak located close to room temperature. These samples also exhibit pinched P–E hysteresis loops. The observed pinching is most probably related to the reorganization of polar nanoregionsmore »under the electric field as shown by synchrotron X-ray diffraction measurements as well as by piezo-response force microscopy analysis, while in part affected by the presence of charged point defects and anti-ferroelectric order, as indicated from rapid cooling experiments and high-resolution transmission electron microscopy, respectively.« less