Chiral symmetry breaking for deterministic switching of perpendicular magnetization by spin-orbit torque

Symmetry breaking is a characteristic to determine which branch of a bifurcation system follows upon crossing a critical point. Specifically, in spin-orbit torque (SOT) devices, a fundamental question arises: how to break the symmetry of the perpendicular magnetic moment by the in-plane spin polarization? Here, we show that the chiral symmetry breaking by the DMI can induce the deterministic SOT switching of the perpendicular magnetization. By introducing a gradient of saturation magnetization or magnetic anisotropy, non-collinear spin textures are formed by the gradient of effective SOT strength, and thus the chiral symmetry of the SOT-induced spin textures is broken by the DMI, resulting in the deterministic magnetization switching. We introduce a strategy to induce an out-of-plane (z) gradient of magnetic properties, as a practical solution for the wafer-scale manufacture of SOT devices.Comment: 16 pages, 4 figure

Genome-Wide Identification and Capsaicinoid Biosynthesis-Related Expression Analysis of the R2R3-MYB Gene Family in Capsicum annuum L.

Capsaicinoids are naturally specialized metabolites in pepper and are the main reason that Capsicum fruits have a pungent smell. During the synthesis of capsaicin, MYB transcription factors play key regulatory roles. In particular, R2R3-MYB subfamily genes are the most important members of the MYB family and are critical candidate factors in capsaicinoid biosynthesis. The 108 R2R3-MYB genes in pepper were identified in this study and all are shown to have two highly conserved MYB binding domains. Phylogenetic and structural analyses clustered CaR2R3-MYB genes into seven groups. Interspecies collinearity analysis found that the R2R3-MYB family contains 16 duplicated gene pairs and the highest gene density is on chromosome 00 and 03. The expression levels of CaR2R3-MYB differentially expressed genes (DEGs) and capsaicinoid-biosynthetic genes (CBGs) in fruit development stages were obtained via RNA-seq and quantitative polymerase chain reaction (qRT-PCR). Co-expression analyses reveal that highly expressed CaR2R3-MYB genes are co-expressed with CBGs during early stages of pericarp and placenta development processes. It is speculated that six candidate CaR2R3-MYB genes are involved in regulating the synthesis of capsaicin and dihydrocapsaicin. This study is the first systematic analysis of the CaR2R3-MYB gene family and provided references for studying their molecular functions. At the same time, these results also laid the foundation for further research on the capsaicin characteristics of CaR2R3-MYB genes in pepper

Distinguishing two-component anomalous Hall effect from topological Hall effect in magnetic topological insulator MnBi2Te4

In transport, the topological Hall effect (THE) is widely interpreted as a sign of chiral spin textures, like magnetic skyrmions. However, the co-existence of two anomalous Hall effects (AHE) could give rise to similar non-monotonic features or "humps", making it difficult to distinguish between the two. Here we demonstrate that the "artifact" two-component anomalous Hall effect can be clearly distinguished from the genuine topological Hall effect by three methods: 1. Minor loops 2. Temperature dependence 3. Gate dependence. One of the minor loops is a single loop that cannot fit into the full AHE loop under the assumption of AHE+THE. In addition, by increasing the temperature or tuning the gate bias, the emergence of humps is accompanied by a polarity change of the AHE. Using these three methods, one can find the humps are from another AHE loop with a different polarity. Our material is a magnetic topological insulator MnBi2Te4 grown by molecular beam epitaxy, where the presence of the secondary phase MnTe2 on the surface contributes to the extra positive AHE component. Our work may help future researchers to exercise cautions and use these three methods to examine carefully in order to ascertain genuine topological Hall effect

Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator

Topological insulators (TI) can apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization with their unique topological surface states, and their magnetic counterparts, magnetic topological insulators (MTI) offer magnetization without shunting and are one of the highest in SOT efficiency. Here, we demonstrate efficient SOT switching of a hard MTI, V-doped (Bi,Sb)2Te3 (VBST) with a large coercive field that can prevent the influence of an external magnetic field and a small magnetization to minimize stray field. A giant switched anomalous Hall resistance of 9.2 $k\Omega$ is realized, among the largest of all SOT systems. The SOT switching current density can be reduced to $2.8\times10^5 A/cm^2$, and the switching ratio can be enhanced to 60%. Moreover, as the Fermi level is moved away from the Dirac point by both gate and composition tuning, VBST exhibits a transition from edge-state-mediated to surface-state-mediated transport, thus enhancing the SOT effective field to $1.56\pm 0.12 T/ (10^6 A/cm^2)$ and the spin Hall angle to $23.2\pm 1.8$ at 5 K. The findings establish VBST as an extraordinary candidate for energy-efficient magnetic memory devices

Exploring the Use of Magnetic Domain Walls and Skyrmions in Beyond-CMOS Memory and Computing Devices

The remarkable advances in complementary metal-oxide-semiconductor (CMOS) electronics have driven significant technological achievements. However, challenges arise from the exponential growth in computational power demanded by artificial intelligence and increasing data volumes. CMOS technology is constrained by the limits of transistor miniaturization and the high energy costs of volatile memory. Spintronics, a Beyond-CMOS technology, leverages the electron’s spin and charge to overcome these limitations, offering non-volatility, fast dynamics, energy-efficient switching, high endurance, and scalability. This positions spintronics as a promising solution for next-generation magnetic memory and logic devices. Magnetic domain walls and skyrmions are topological excitations that extend beyond the uniform ferromagnetic background. These spin textures inherit the notable advantages of spintronics and function effectively as solitonic information carriers for memory and computing applications. Moreover, they provide significant improvements in energy and area efficiency compared to traditional uniform magnetization-based spintronics. Driven by these motivations, my doctoral study focuses on developing domain wall- and skyrmion-based memory and computing devices. In this dissertation, we explore the Dzyaloshinskii-Moriya interaction, which is the fundamental mechanism underlying domain walls and skyrmions. We present our development of the voltage-controlled Dzyaloshinskii-Moriya interaction and utilize this effect to control skyrmion motion, addressing the challenge of the skyrmion Hall effect in skyrmion racetrack memory. Additionally, we delve into physically-inspired non-Boolean computing paradigms, utilizing the spintronic mechanism of domain wall motion to create magnetic convolution hardware and demonstrating its algorithmic implementations. Furthermore, we have discovered a transient antiskyrmion state in an isotropic Dzyaloshinskii-Moriya interaction system and have clarified its underlying mechanism. Leveraging the stochastic nature of this state, we demonstrate the potential for developing a true random number generator

The chloroplast genome of silk floss tree (Ceiba speciosa)

Ceiba speciosa (Malvaceae), also called silk floss tree, is a beautiful and deciduous tree native to tropical and subtropical forests of South America. Its phylogenetic position remains unclear. In this study, the complete chloroplast genome sequence of C. speciosa was reported. Its chloroplast genome size was 160,360 bp, which contains a small single copy (SSC) region of 19,947 bp and a large single copy region (LSC) of 89,393 bp, and two inverted repeats (IRs) of 25,510 bp each. In total, 129 genes were annotated for the chloroplast genome, including 86 protein-coding genes, 37 tRNA genes and 8 rRNA genes. Phylogenetic analysis showed that C. speciosa was sister to Bombax ceiba