Xiaofeng Xu

Nonreciprocal charge transport, where current flows preferentially in one direction, has become a key topic across quantum materials. This review covers some recent progress in bulk crystals, artificial heterostructures, van der Waals systems, high-temperature superconductors, and magnetic materials. The review discusses both intrinsic origins, such as band-structure effects, and extrinsic ones, including vortex motion, device geometry, and heating artifacts. A central focus is the superconducting diode effect due to its application potential, which shows different critical currents for opposite directions. The review also examines how symmetry breaking, spin–orbit coupling, and magnetic order contribute to the observed responses. However, there remain challenges when many exciting findings lack a unified picture, and the field continues to debate the relative importance of various mechanisms. The review highlights key open questions and suggests future directions, including better experimental standards and device integration. This review aims to give a balanced view of what is known, what is uncertain, and where the field might go next.

Superconductivity emerging from or in the vicinity of magnetic states is generally considered to be mediated by spin fluctuations and thus lies beyond the scope of conventional electron‐phonon coupled BCS framework. Here we report the emergence of novel ferromagnetism in the d ‐electron rhodium sulfide Rh ₁₇ S ₁₅ superconductor, characterized by an enhanced Sommerfeld coefficient γ arising from the flat topological band and many‐body correlations. We further demonstrate that the ferromagnetism can be tuned via Fe substitution at the Rh sites, leading to a spin glass ground state induced by the competing ferromagnetic and antiferromagnetic exchange interactions. Fe doping results in a further enhancement of both the γ and electron effective masses. At a doping level of x = 0.67 in Rh _{17‐ x} Fe _x S ₁₅ , γ reaches 312 mJ mol ⁻¹ K ⁻² , second only to the well‐documented d ‐electron heavy‐fermion material LiV ₂ O ₄ . Furthermore, upon applying pressure, superconductivity is first suppressed; under high pressures, however, we observe the reentrant superconductivity in both pristine and Fe‐doped samples. Our results not only demonstrate the unusual magnetic states and possible heavy‐fermion features in these frustration‐free, d ‐based superconductors, but also suggest that the superconductivity in this system is likely mediated by the intrinsic spin fluctuations and may thus be unconventional.

Topological materials that simultaneously host robust high‐temperature skyrmions and nontrivial electronic band structures have attracted tremendous interest owing to their distinctive advantages for both fundamental research and prospective technological applications. Here, we report the observation of robust skyrmions in the Dirac kagome magnet Fe ₃ Ge, which exhibits a high Curie temperature of ∼ 650 K. At room temperature, Fe ₃ Ge shows a large intrinsic anomalous Hall conductivity of ∼ 380 Ω ⁻¹ cm ⁻¹ , originating from its nontrivial electronic band topology. Systematic magnetization measurements reveal a spin reorientation transition at ∼ 375 K, indicating a crossover from easy‐plane to easy‐axis magnetic anisotropy. Below the spin reorientation temperature, a large topological Hall effect is observed, arising from microscopic noncoplanar spin structures. Lorentz transmission electron microscopy shows that mesoscopic skyrmions are stabilized in the easy‐axis magnetic anisotropy regime and persist over an exceptionally wide temperature window of 375–650 K, far exceeding that of most previously reported skyrmion‐hosting materials. These results establish Fe ₃ Ge as a promising platform for exploring diverse topological properties, with strong potential for advancing future high‐temperature spintronic applications, ranging from next‐generation information storage to logic computing devices.