Highly Efficient Room-Temperature Spin-Orbit-Torque Switching in a Van der Waals Heterostructure of Topological Insulator and Ferromagnet.

All-Van der Waals (vdW)-material-based heterostructures with atomically sharp interfaces offer a versatile platform for high-performing spintronic functionalities at room temperature. One of the key components is vdW topological insulators (TIs), which can produce a strong spin-orbit-torque (SOT) through the spin-momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge-to-spin conversion efficiency (qICS). Here, a vdW heterostructure is used consisting of atomically-thin layers of a bulk-insulating TI Sn-doped Bi1.1Sb0.9Te2S1 and a room-temperature ferromagnet Fe3GaTe2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting qICS reaches ≈1.65 nm-1 and the critical current density Jc ≈0.9 × 106 Acm-2 at 300 K, surpassing the performance of TI-based and heavy-metal-based SOT devices. These findings demonstrate that an all-vdW heterostructure with thickness optimization offers a promising platform for efficient current-controlled magnetization switching at room temperature.

Spin-Orbit Torque Switching in an All-Van der Waals Heterostructure.

Current-induced control of magnetization in ferromagnets using spin-orbit torque (SOT) has drawn attention as a new mechanism for fast and energy efficient magnetic memory devices. Energy-efficient spintronic devices require a spin-current source with a large SOT efficiency (ξ) and electrical conductivity (σ), and an efficient spin injection across a transparent interface. Herein, single crystals of the van der Waals (vdW) topological semimetal WTe2  and vdW ferromagnet Fe3 GeTe2 are used to satisfy the requirements in their all-vdW-heterostructure with an atomically sharp interface. The results exhibit values of ξ ≈ 4.6 and σ ≈ 2.25 × 105  Ω-1 m-1 for WTe2 . Moreover, the significantly reduced switching current density of 3.90 × 106 A cm-2 at 150 K is obtained, which is an order of magnitude smaller than those of conventional heavy-metal/ferromagnet thin films. These findings highlight that engineering vdW-type topological materials and magnets offers a promising route to energy-efficient magnetization control in SOT-based spintronics.

Dissecting landscape art history with information theory.

Painting has played a major role in human expression, evolving subject to a complex interplay of representational conventions, social interactions, and a process of historization. From individual qualitative work of art historians emerges a metanarrative that remains difficult to evaluate in its validity regarding emergent macroscopic and underlying microscopic dynamics. The full scope of granular data, the summary statistics, and consequently, also their bias simply lie beyond the cognitive limit of individual qualitative human scholarship. Yet, a more quantitative understanding is still lacking, driven by a lack of data and a persistent dominance of qualitative scholarship in art history. Here, we show that quantitative analyses of creative processes in landscape painting can shed light, provide a systematic verification, and allow for questioning the emerging metanarrative. Using a quasicanonical benchmark dataset of 14,912 landscape paintings, covering a period from the Western renaissance to contemporary art, we systematically analyze the evolution of compositional proportion via a simple yet coherent information-theoretic dissection method that captures iterations of the dominant horizontal and vertical partition directions. Tracing frequency distributions of seemingly preferred compositions across several conceptual dimensions, we find that dominant dissection ratios can serve as a meaningful signature to capture the unique compositional characteristics and systematic evolution of individual artist bodies of work, creation date time spans, and conventional style periods, while concepts of artist nationality remain problematic. Network analyses of individual artists and style periods clarify their rhizomatic confusion while uncovering three distinguished yet nonintuitive supergroups that are meaningfully clustered in time.