Enhanced Stability of the Magnetic Skyrmion Lattice Phase under a Tilted Magnetic Field in a Two-Dimensional Chiral Magnet

The magnetic skyrmion is a topologically stable vortex-like spin texture that offers great promise as information carriers for future spintronic devices. In a two-dimensional chiral magnet, it was generally considered that a tilted magnetic field is harmful to its formation and stability. Here we investigated the angular-dependent stability of magnetic skyrmions in FeGe nanosheets by using high-resolution Lorentz transmission electron microscopy (Lorentz TEM). Besides the theoretically predicted destruction of skyrmion lattice state by an oblique magnetic field as the temperature closes to its magnetic Curie temperature <i>T</i>_c ∼ 278 K, we also observed an unexpected reentry-like phenomenon at the moderate temperatures near the border between conical and skyrmion phase, <i>T</i>_t ∼ 240 K. This behavior is completely beyond the theoretical prediction in a conventional two-dimensional (2D) system. Instead, a three-dimensional (3D) model involving the competition between conical phase and skyrmions is likely to play a crucial role

Thermal Stability of Skyrmion Tubes in Nanostructured Cuboids

Magnetic skyrmions in bulk materials are typically regarded as two-dimensional structures. However, they also exhibit three-dimensional configurations, known as skyrmion tubes, that elongate and extend in-depth. Understanding the configurations and stabilization mechanism of skyrmion tubes is crucial for the development of advanced spintronic devices. However, the generation and annihilation of skyrmion tubes in confined geometries are still rarely reported. Here, we present direct imaging of skyrmion tubes in nanostructured cuboids of a chiral magnet FeGe using Lorentz transmission electron microscopy (TEM), while applying an in-plane magnetic field. It is observed that skyrmion tubes stabilize in a narrow field-temperature region near the Curie temperature (Tc). Through a field cooling process, metastable skyrmion tubes can exist in a larger region of the field-temperature diagram. Combining these experimental findings with micromagnetic simulations, we attribute these phenomena to energy differences and thermal fluctuations. Our results could promote topological spintronic devices based on skyrmion tubes

Evidence of Topological Two-Dimensional Metallic Surface States in Thin Bismuth Nanoribbons

Understanding the exotic quantum phenomena in bulk bismuth beyond its ultraquantum limit remains controversial and gives rise to renewed interest. The focus of the issues is whether these quantum properties have a conventional bulk nature or just the surface effect due to the significant spin–orbital interaction and in relation to the Bi-based topological insulators. Here, we present angular-dependent magnetoresistance (AMR) measurements on single-crystal bismuth nanoribbons of different thicknesses with magnetic fields up to 31 T. In thin nanoribbons with thickness of ∼40 nm, a two-fold rational symmetry of the low field AMR spectra and two sets of 1/2-shifted (<i>i.e., </i>γ = 1/2) Shubnikov–de Haas (SdH) quantum oscillations with exact two- dimensional (2D) character were obtained. However, when the thickness of the ribbon increases, a 3D bulk-like SdH oscillations with γ = 0 and a four-fold rotational symmetry of the AMR spectra appear. These results provided unambiguous transport evidence of the topological 2D metallic surface states in thinner nanoribbons with an insulating bulk. Our observations provide a promising pathway to understand the quantum phenomena in Bi arising from the surface states

Superconductor–Insulator Transition in Quasi-One-Dimensional Single-Crystal Nb₂PdS₅ Nanowires

Superconductor–insulator transition (SIT) in one-dimensional (1D) nanowires attracts great attention in the past decade and remains an open question since contrasting results were reported in nanowires with different morphologies (i.e., granular, polycrystalline, or amorphous) or environments. Nb₂PdS₅ is a recently discovered low-dimensional superconductor with typical quasi-1D chain structure. By decreasing the wire diameter in the range of 100–300 nm, we observed a clear SIT with a 1D transport character driven by both the cross-sectional area and external magnetic field. We also found that the upper critical magnetic field (<i>H</i>_c2) decreases with the reduction of nanowire cross-sectional area. The temperature dependence of the resistance below <i>T</i>_c can be described by the thermally activated phase slip (TAPS) theory without any signature of quantum phase slips (QPS). These findings demonstrated that the enhanced Coulomb interactions with the shrinkage of the wire diameter competes with the interchain Josephson-like coupling may play a crucial role on the SIT in quasi-1D system

Superconductor–Insulator Transition in Quasi-One-Dimensional Single-Crystal Nb₂PdS₅ Nanowires

Superconductor–insulator transition (SIT) in one-dimensional (1D) nanowires attracts great attention in the past decade and remains an open question since contrasting results were reported in nanowires with different morphologies (i.e., granular, polycrystalline, or amorphous) or environments. Nb₂PdS₅ is a recently discovered low-dimensional superconductor with typical quasi-1D chain structure. By decreasing the wire diameter in the range of 100–300 nm, we observed a clear SIT with a 1D transport character driven by both the cross-sectional area and external magnetic field. We also found that the upper critical magnetic field (<i>H</i>_c2) decreases with the reduction of nanowire cross-sectional area. The temperature dependence of the resistance below <i>T</i>_c can be described by the thermally activated phase slip (TAPS) theory without any signature of quantum phase slips (QPS). These findings demonstrated that the enhanced Coulomb interactions with the shrinkage of the wire diameter competes with the interchain Josephson-like coupling may play a crucial role on the SIT in quasi-1D system