MMagnetic skyrmions are vortex-like spin configurations that possess nanometric dimensions, topological stability, and high controllability through various external stimuli. Since their first experimental observation in helimagnet MnSi in 2009, magnetic skyrmions have emerged as a highly promising candidate for carrying information in future high-performance, low-energy-consumption, non-volatile information storage, and logical calculation. In this article, we provide a comprehensive review of the progress made in the field of magnetic skyrmions, specifically in materials, manipulation, detection, and application in spintronic devices. Firstly, we introduce several representative skyrmion material systems, including chiral magnets, magnetic thin films, centrosymmetric materials, and Van der Waals materials. We then discuss various methods for manipulating magnetic skyrmions, such as electric current and electric field, as well as detecting them, mainly through electrical means such as the magnetoresistance effect. Furthermore, we explore device applications based on magnetic skyrmions, such as track memory, logic computing, and neuromorphic devices. Finally, we summarize the challenges faced in skyrmion research and provide future perspectives.
Abstract: Two-dimensional (2D) graphdiyne (GDY)-based materials have attracted attention in the solar cell research community owing to their unique physicochemical properties and hydrophobic nature which can serve as moisture resistance from the surrounding medium. Benefiting from these, the performance and stability ofperovskite solar cells (PSCs) can be greatly improved via the addition of 2D GDY-based materials. This mini-review summarizes the recent development of 2D GDY-based materials for PSC application. The roles of 2D GDY-based materials, such as hole transporting material, electron transporting material, dopant material in perovskite film and interfacial layer, are discussed in detail. Moreover, we provide future perspectives in this field, aiming to help further progress efficient and stable 2D GDY-based materials in PSCs.
Based on symmetry analysis and lattice model calculations, we demonstrate that Dirac nodal line (DNL) can stably exist in two-dimensional (2D) nonmagnetic as well as antiferromagnetic systems. We focus on the situations where the DNLs are enforced by certain symmetries and the degeneracies on the DNLs are inevitable even if spin–orbit coupling is strong. After thorough analysis, we find that five space groups, namely 51, 54, 55, 57 and 127, can enforce the DNLs in 2D nonmagnetic semimetals, and four type-III magnetic space groups (51.293, 54.341, 55.355, 57.380) plus eight type-IV magnetic space groups (51.299, 51.300, 51.302, 54.348, 55.360, 55.361, 57.387 and 127.396) can enforce the DNLs in 2D antiferromagnetic semimetals. By breaking these symmetries, the different 2D topological phases can be obtained. Furthermore, by the first-principles electronic structure calculations, we predict that monolayer YB4C4 is a good material platform for studying the exotic properties of 2D symmetry-enforced Dirac node-line semimetals.
Rhodium-containing compounds offer a fertile playground to explore novel materials with superconductivity (SC) and other fantastic electronic correlation effects. A new ternary rhodium-antimonide La2Rh3+δSb4 (δ≈1/8) has been synthesized by a Bi-flux method. It crystallizes in the orthorhombic Pr2Ir3Sb4-like structure, with the space group Pnma (No. 62). The crystalline structure appears as stacking the two-dimensional RhSb4- and RhSb5-polyhedra networks along b axis, and the La atoms embed in the cavities of these networks. Band structure calculations confirm it as a multi-band metal with a van-Hove singularity like feature at the Fermi level, whose density of states are mainly of Rh-4d and Sb-5p characters. The calculations also imply that the redundant Rh acts as charge dopant. SC is observed in this material with onset transition at Tcon≈0.8 K. Ultra-low temperature magnetic susceptibility and specific heat measurements suggest that it is an s-wave type-II superconductor. Our work may also imply that the broad Ln2Tm3+δSb4 (Ln = rare earth, Tm = Rh, Ir) family may host new material bases where new superconductors, quantum magnetism and other electronic correlation effects could be found.
High harmonic generation (HHG) delivering attosecond pulse duration with photon energy in the extreme ultraviolet spectral range has been demonstrated as a robust table-top coherent light source, allowing for the observation and manipulation of ultrafast process within the shortest time window ever made by humans. The past decade has witnessed the rapid progress of HHG from a variety of solid targets and its application for photoemission spectroscopy in condensed matter. In this article, we review the HHG in solids and the understanding of the underlying physics of HHG, which allows all-optical band structure reconstruction. We also introduce combinations of HHG source and photoemission spectroscopy, such as angular-resolved photoemission spectroscopy and photoemission electron microscopy. With the capacity of exploring a wide momentum space and high temporal resolution, the extension of attosecond science to the field of condensed matter physics will lead to new insights into the fundamental ultrafast dynamics in novel quantum materials.
In recent years, topological quantum materials (TQMs) have attracted intensive attention in the area of condensed matter physics due to their novel topologies and their promising applications in quantum computing, spin electronics and next-generation integrated circuits. Scanning tunneling microscopy/spectroscopy (STM/STS) is regarded as a powerful technique to characterize the local density of states with atomic resolution, which is ideally suited to the measurement of the bulk-boundary correspondence of TQMs. In this review, using STM/STS, we focus on recent research on bismuth-based TQMs, including quantum-spin Hall insulators, 3D weak topological insulators (TIs), high-order TIs, topological Dirac semi-metals and dual TIs. Efficient methods for the modulation of the topological properties of the TQMs are introduced, such as interlayer interaction, thickness variation and local electric field perturbation. Finally, the challenges and prospects for this field of study are discussed.
All-electrical driven magnetization switching attracts much attention in next-generation spintronic memory and logic devices, particularly in magnetic random-access memory (MRAM) based on the spin–orbit torque (SOT), i.e. SOT-MRAM, due to its advantages of low power consumption, fast write/read speed, and improved endurance, etc. For conventional SOT-driven switching of the magnet with perpendicular magnetic anisotropy, an external assisted magnetic field is necessary to break the inversion symmetry of the magnet, which not only induces the additional power consumption but also makes the circuit more complicated. Over the last decade, significant effort has been devoted to field-free magnetization manipulation by using SOT. In this review, we introduce the basic concepts of SOT. After that, we mainly focus on several approaches to realize the field-free deterministic SOT switching of the perpendicular magnet. The mechanisms mainly include mirror symmetry breaking, chiral symmetry breaking, exchange bias, and interlayer exchange coupling. Furthermore, we show the recent progress in the study of SOT with unconventional origin and symmetry. The final section is devoted to the industrial-level approach for potential applications of field-free SOT switching in SOT-MRAM technology.
Conjugated polymers (CPs), organic macromolecules with a linear backbone of alternating C–C and C=C bonds, possess unique semiconductive properties, providing new opportunities for organic electronics, photonics, information, and energy devices. Seeking the metallic or metallic-like, even superconducting properties beyond semiconductivity in CPs is always one of the ultimate goals in polymer science and condensed matter. Only two metallic and semi-metallic transport cases—aniline-derived polyaniline and thiophene-derived poly(3,4-ethylenedioxythiophene)—have been reported since the development of CPs for four decades. Controllable synthesis is a key challenge in discovering more cases. Here we report the metallic-like transport behavior of another CP, polypyrrole (PPy). We observe that the transport behavior of PPy changes from semiconductor to insulator-metal transition, and gradually realizes metallic-like performance when the crystalline degree increases. Using a generalized Einstein relation model, we rationalized the mechanism behind the observation. The metallic-like transport in PPy demonstrates electron strong correlation and phonon–electron interaction in soft condensation matter, and may find practical applications of CPs in electrics and spintronics.