Yuyan Han

High-quality BaCuO2 single crystals were successfully grown by a high-temperature BaCl2·2H2O flux method under an optimal slow-cooling condition of 1 °C/h within the temperature window of 980–800 °C. Structural characterizations confirm that BaCuO2 crystallizes in the cubic Im-3m structure with excellent crystallinity, homogeneous elemental distribution, and negligible oxygen-vacancy concentration. Magnetic susceptibility, magnetization, and specific-heat measurements consistently reveal an antiferromagnetic transition near TN = 11 K accompanied by pronounced short-range magnetic correlations. Although the Curie–Weiss fitting yields a positive Weiss temperature, the low-temperature thermodynamic response establishes an antiferromagnetic ground state arising from competing magnetic exchange interactions within the Cu–O cluster network. Importantly, the present single-crystal study demonstrates that BaCuO2 is intrinsically an insulating oxide rather than a semiconducting or superconductivity-related material, highlighting the crucial importance of high-quality single crystals for distinguishing intrinsic physical properties from impurity-driven effects in complex cuprate systems.

The spin supersolid—a magnetic analogue of the supersolid that simultaneously exhibits solid and superfluid orders—has emerged as a promising sub-Kelvin refrigerant with strong low-energy fluctuations and associated entropic effects¹. However, the stringent prerequisites have so far confined its presence to certain magnetic insulators. Here we report the discovery of a metallic spin supersolid in a rare-earth compound EuCo₂Al₉ (ECA), which is a good metal with excellent electrical and thermal conductivity. The high-spin Eu²⁺ ions form a three-dimensional lattice with stacked triangular layers, in which the spin-supersolid state is stabilized through a mechanism involving both Ruderman–Kittel–Kasuya–Yosida (RKKY) and dipolar couplings. Neutron diffraction shows microscopic evidence of spin supersolidity, demonstrating the coexistence of out-of-plane and in-plane spin orders in this alloy. Our RKKY–dipolar model successfully captures the metallic spin-supersolid Y and V phases in ECA, along with the 1/3 magnetization plateau. The observed nonclassical magnetization behaviours within these phases point to significant quantum fluctuations, probably enhanced by the conduction electrons. The resistivity measurements provide a transport probe for the spin-supersolid transitions, because of scattering of conduction electrons from local moments. Through the adiabatic demagnetization process, ECA achieves ultralow cooling to 106 mK, exhibiting a giant magnetocaloric effect that manifests sharp anomalies in the magnetic Grüneisen ratio. ECA emerges as one of the first metallic spin supersolids, combining low cooling temperature, large magnetic entropy and ultrahigh thermal conductivity for high-performance sub-Kelvin refrigeration.

Rare-earth tritellurides (RTe3, R = lanthanide) represent an ideal platform for investigating charge density wave (CDW) order and associated Fermi surface reconstructions. While quantum oscillations have been observed in several RTe3 members, a detailed exploration of the low-temperature electronic transport properties of high-quality SmTe3 single crystals remains limited. In this study, we synthesized SmTe3 single crystals with a high residual resistivity ratio of 411. Transport measurements reveal pronounced Shubnikov–de Haas quantum oscillations below 30 K. The carriers in the observed Fermi pockets exhibit an extremely small effective mass of 0.119 m0 and a high mobility reaching 3.78×104 cm2 V−1 s−1. Furthermore, the material demonstrates remarkable anisotropic magnetoresistance, indicative of a highly anisotropic Fermi surface. Our work establishes high-quality SmTe3 as a compelling system for studying high-mobility transport in a CDW background, providing crucial insights for potential applications in advanced electronic devices.

The interplay between symmetry breaking, spin-orbit coupling, and magnetic frustration in noncentrosymmetric antiferromagnets has emerged as a fertile ground for discovering intertwined topological and quantum phenomena. Here, we report a cascade of magnetic phase transitions and a large topological Hall response in the newly discovered noncentrosymmetric antiferromagnetic (AFM) material Eu 2 Pd 3 Bi 4 with a Neél temperature T N = 7.6 K . Under magnetic fields ( H ) parallel to the c axis, two successive phase transitions at critical fields H 1 and H 2 are observed in magnetization at temperatures below T N , which are attributed to the occurrences of sequential field-induced spin states. A pronounced topological Hall effect signal emerges exclusively within an intermediate field window H 1 < H < H 2 , signifying the formation of topological spin textures. The field-temperature phase diagram mapped via specific heat and magnetoelectric transport measurements incorporates five phase regimes: The paramagnetic state, a high-field polarized state, and three AFM states with distinct spin configurations. Our results identify Eu 2 Pd 3 Bi 4 as a good candidate for scrutinizing sophisticated interplays between magnetic structure and nontrivial band topology.

Solid-state refrigeration leveraging the magnetocaloric effect (MCE) presents a sustainable and energy-efficient alternative to traditional gas compression refrigeration technologies. However, the practical utility of most magnetocaloric materials is restricted by their narrow operational temperature window. In this work, a stable magnetocaloric effect across an ultrawide temperature range of 146–320 K was achieved in Hf0.85Ta0.15Fe2 magnet via the hydrostatic pressure manipulation. Furthermore, the underlying mechanism for the extended and stable MCEs under hydrostatic pressure has been revealed by magnetization measurements and first-principles calculations. The material systems characterized by strong spin–lattice coupling exhibit considerable potential for externally manipulated hybrid-field-tuned magnetic properties and magnetocaloric performance, providing a convenient and practical approach for advancing applications in magnetic refrigeration technologies.

The observation of the planar Hall effect (PHE) illuminates the spin textures and topological properties of materials, indicating potential applications in quantum computing and electronic devices. Here, we present a study on the planar Hall transport of topological insulator NaCd4As3 single crystals. When the magnetic field is rotated within the sample plane relative to the current direction, we observe remarkable planar Hall resistivity and giant planar anisotropic magnetoresistance (AMR), both consistent with the theoretical expression of the PHE. Further analysis reveals that the orbital magnetoresistance effect, unrelated to surface electrons from topological surface states or bulk electrons from nontrivial Berry phases, lays a dominant role in the PHE in NaCd4As3. Additionally, the AMR ratio reaches −43% at 3 K under 14 T and remains −9% at room temperature, markedly exceeding that of traditional ferromagnetic metals. These findings provide a platform for understanding the PHE mechanism in topological insulators and highlight the potential of NaCd4As3 for angle and magnetic field detection applications.