We report 59Co and 71Ga nuclear magnetic resonance investigations of the quasi-one-dimensional Kondo lattice compound CeCo2Ga8. Below the coherence temperature, T* approximate to 29 K, the Knight shift, as well as the nuclear spin-spin relaxation rate, the nuclear spin-lattice relaxation rate exhibits anomalous temperature-dependent behaviors. The universal scaling of the Knight shift anomaly with temperature is in accordance with the predictions of the two-fluid model. Unlike many other heavy fermion materials, the spin-lattice relaxation rate shows a broad minimum around T*, precisely concurrent with a rapid increase in the spin-spin relaxation rate below T*. Our analysis suggests an enhancement of the antiferromagnetic correlation length or time below T*, which might contribute to the emergence of heavy-electron behavior.

Van der Waals (vdW) magnetic materials have emerged as a promising platform for investigating low-dimensional magnetism and developing next-generation spintronic devices. Among them, all-ferromagnetic heterojunctions, such as the Fe3GaTe2/Fe3GeTe2 (FGaT/FGT) system, exhibit intriguing magneto transport phenomena, including multi-step transitions and antisymmetric magnetoresistance (MR) peaks under perpendicular magnetic fields. However, the underlying physical mechanisms governing these complex behaviors remain elusive. This study aims to elucidate the origin of the antisymmetric MR in FGaT/FGT vdW heterojunctions, focusing on the interplay between the anomalous Hall effect (AHE), interfacial oxidation, and temperature-dependent interlayer coupling. High-quality FGaT/FGT heterojunction devices were fabricated using mechanical exfoliation and dry transfer techniques. The magneto transport properties were systematically characterized from 5 K to 190 K using a physical property measurement system (PPMS). The experimental results, combined with an equivalent circuit model analysis, reveal that the antisymmetric MR signal primarily stems from a local non-equilibrium current driven by a mismatch in the AHE voltages generated across the top (FGT) and bottom (FGaT) ferromagnetic layers when their magnetizations are non-collinear. This voltage imbalance significantly modulates the longitudinal resistance (R-xx), producing the characteristic sharp MR peaks near zero field. Furthermore, detailed analysis of the individual FGaT layer uncovers a two-stage magnetization reversal process, attributed to the coexistence of a magnetically distinct interface region, influenced by a naturally formed antiferromagnetic O-FGaT oxide layer, and the FGaT bulk region. This interfacial oxidation induces an exchange bias effect, which is responsible for the observed asymmetry and multi-step transitions in the heterojunction's MR hysteresis loops. Temperature-dependent measurements demonstrate that the antisymmetric MR diminishes upon heating, evolving into a smooth, paramagnetic-like background above 180 K. This transition highlights the suppression of the AHE-driven non-equilibrium transport and the interlayer decoupling as thermal fluctuations reduce magnetic anisotropy. In conclusion, our work demonstrates that the antisymmetric MR in FGaT/FGT heterojunctions arises from the synergistic effects of AHE-induced circulating currents, interface oxidation-mediated exchange bias, and thermally activated layer decoupling. These findings provide a comprehensive understanding of the charge transport mechanisms at magnetic vdW interfaces and offer valuable insights for the design of future multi-state spintronic devices based on interface and domain engineering.

This corrects the article DOI: 10.1103/pywx-vxfh.

Interactions of collective excitations often lead to rich emergent phenomena in many-particle quantum systems. In ordered magnets, the elementary excitations are spin waves (magnons), which obey Bose-Einstein statistics. Similar to the Cooper pairs in superconductors, magnons can be paired into bound states under attractive interactions. Even more interestingly, the Zeeman coupling to a magnetic field acts as a chemical potential that can tune the particle density through a quantum critical point (QCP), beyond which a ``hidden order'' is predicted to exist. However, experimental confirmation of this QCP and the associated new state of matter remain elusive. Here we report direct observation of the Bose-Einstein condensation (BEC) of the two-magnon bound state in Na$_2$BaNi(PO$_4$)$_2$. Comprehensive thermodynamic measurements confirmed the existence of a two-dimensional BEC-QCP at the saturation field. Inelastic neutron scattering experiments were performed to accurately establish the magnetic exchange model. An exact solution of the model found stable 2-magnon bound states that were further confirmed by an electron spin resonance (ESR) experiment, demonstrating that the QCP is due to the pair condensation and the phase below saturation field is the long-sought-after spin nematic (SN) phase.

Information technology has a great demand for magnetoresistance (MR) sensors with high sensitivity and wide-temperature-range operation. It is well known that space charge inhomogeneity in graphene (Gr) leads to finite MR in its pristine form, and can be enhanced by increasing the degree of spatial disorder. However, the enhanced MR usually diminishes drastically as the temperature decreases. Here, by stacking a van der Waals ferromagnet Fe3GeTe2 (FGT) on top of graphene to form an FGT/Gr heterostructure, we demonstrate a positive MR of up to ~9400% under a magnetic field of 9 T at room temperature (RT), an order of magnitude larger MR compared to pure graphene. More strikingly, the giant MR of the FGT/Gr heterostructure sustains over a wide temperature range from RT down to 4 K. Both control experiments and DFT calculations show that the enhanced MR originates from spin-dependent orbital coupling between FGT and graphene, which is temperature insensitive. Our results open a new route for realizing high-sensitivity and wide-temperature-range MR sensors. Graphene is known to exhibit a magnetoresistance, however, in pristine graphene, the magnetoresistance is highly temperature sensitive. Here, by combining graphene with Fe3GeTe2, Huang et al find a strongly enhanced magnetoresistance that is temperature insensitive.

Discovery of new states of matter is a key objective in modern condensed matter physics, which often leads to revolutionary technological advancements such as superconductivity. Quantum spin nematic, a “hidden order” that evades conventional magnetic probes, is one such state. Na_2BaNi(PO_4)_2 is a potential spin nematic material, suggested by the observation of a two-magnon Bose-Einstein condensation from above the saturation field. However, direct confirmation of the spin nematicity remains elusive. This Letter presents inelastic neutron scattering spectra from the putative spin nematic phases of Na_2BaNi(PO_4)_2, revealing low-energy quadrupole waves that are absent in the neighboring conventional magnetic phases. A spin-one model quantitatively captures the full details of the spin excitation spectra across all low-temperature phases, providing direct evidence of the spin nematic orders. Additionally, we show evidence of the three-magnon continuum and two-magnon bound states in the 1/3-magnetization plateau, revealing condensation of the two-magnon bound state as the origin of the low-field spin nematic supersolid phase.

We investigate the magnetic phase diagram of the bilayer triangular antiferromagnet K$_2$Co$_2$(SeO$_3$)$_3$, unveiling a rich interplay between geometric frustration, bilayer coupling, and symmetry-driven phenomena. High-field magnetization measurements reveal fractional magnetization plateaus at 1/3, 1/2, 2/3, and 5/6 of the saturation magnetization. To elucidate the experimental magnetic phase diagram at low fields, we propose that K$_2$Co$_2$(SeO$_3$)$_3$ can be described as an easy-axis triangular weak-dimer antiferromagnet. We emphasize the critical role of the emergent $U(1) \otimes S_3$ symmetry, where $S_3 = \mathbb{Z}_3 \otimes \mathbb{Z}_2^d$, in determining the magnetic phases at low fields. The remarkable agreement between the experimental and theoretical phase diagrams suggests that the phase transitions are governed by this symmetry. Notably, our combined experimental and theoretical results identify a Berezinskii-Kosterlitz-Thouless (BKT) phase region at finite fields. These findings provide new insights into the phase structure of frustrated magnets and establish K$_2$Co$_2$(SeO$_3$)$_3$ as a compelling platform for exploring unconventional quantum phenomena in $U(1) \otimes S_3$ systems.

Interlayer magnetic interactions play a pivotal role in determining the magnetic arrangement within van der Waals (vdW) magnets, and the remarkable tunability of these interactions through applied pressure further enhances their significance. Here, we investigate NiI2 flakes, a representative vdW magnet, under hydrostatic pressures up to 11 GPa. We reveal a notable increase in magnetic transition temperatures for both helimagnetic and antiferromagnetic states, and find that a reversible transition from helimagnetic to antiferromagnetic (AFM) phases at approximately 7 GPa challenges established theoretical and experimental expectations. While the increase in transition temperature aligns with pressure-enhanced overall exchange interaction strengths, we identify the significant role of the second-nearest neighbor interlayer interaction, which competes with intra-layer frustration and favors the AFM state as demonstrated in the Monte Carlo simulations. Experimental and simulated results converge on the existence of an intermediate helimagnetic ordered state in NiI2 before transitioning to the AFM state. These findings underscore the pivotal role of interlayer interactions in shaping the magnetic ground state, providing fresh perspectives for innovative applications in nanoscale magnetic device design.

Three key aspects of magnetic topological materials, i.e., band topology, magnetic order and anomalous transport are closed related with each other, laying the ground for exotic phenomena such as topological magnetoelectric and magneto-optical effects. Here in the ferromagnetic Weyl semimetal PrAlSi, we report negligible effect of magnetic order on the band structure featuring Weyl fermions, as directly observed by angle-resolved photoemission spectroscopy. Instead, both anomalous and normal Hall effects show clear temperature/magnetism dependence. While the longitudinal conductivity ( σ_xx ) is deep in the empirically intrinsic region, the anomalous Hall conductivity ( σ_AHE ) is quadratically proportional to σ_xx , suggesting giant anomalous Hall angle at moderate σ_xx . Our findings point to disentangled band topology and anomalous transport, as well as the possibility to achieve high σ_AHE in highly conductive, ultrathin PrAlSi, suitable for anomalous Hall sensors and spin-transfer torque application. Magnetic topological materials exhibit intertwined band topology, magnetic order, and anomalous transport, leading to unique phenomena. Here, the authors study the ferromagnetic Weyl semimetal PrAlSi, revealing negligible magnetic order effects on Weyl fermions but significant temperature-dependent Hall effects, including a giant anomalous Hall angle, suggesting potential for high-performance anomalous Hall sensors and spin-transfer torque applications.

The complex interplay of spin frustration and quantum fluctuations in low-dimensional quantum materials leads to a variety of intriguing phenomena. This research focuses on a detailed analysis of the magnetic behavior exhibited by NdZnPO, a bilayer spin-1/2 triangular lattice antiferromagnet. The investigation employs magnetization, specific heat, and powder neutron scattering measurements. At zero field, a long-range magnetic order is observed at $T_{\rm N}=1.64~\rm K$. Powder neutron diffraction experiments show the Ising-like magnetic moments along the $c$-axis, revealing a stripe-like magnetic structure with three equivalent magnetic propagation vectors. Application of a magnetic field along the $c$-axis suppresses the antiferromagnetic order, leading to a fully polarized ferromagnetic state above $B_{\rm c}=4.5~\rm T$. This transition is accompanied by notable enhancements in the nuclear Schottky contribution. Moreover, the absence of spin frustration and expected field-induced plateau-like phases are remarkable observations. Detailed calculations of magnetic dipolar interactions revealed complex couplings reminiscent of a honeycomb lattice, suggesting the potential emergence of Kitaev-like physics within this system. This comprehensive study of the magnetic properties of NdZnPO highlights unresolved intricacies, underscoring the imperative for further exploration to unveil the underlying governing mechanisms.

Quantum confinement is a restriction on the motion of electrons in a material to specific region, resulting in discrete energy levels rather than continuous energy bands. In certain materials, quantum confinement could dramatically reshape the electronic structure and properties of the surface with respect to the bulk. Here, in the recently discovered kagome superconductors CsV 3 Sb 5 , we unveil the dominant role of quantum confinement in determining their surface electronic structure. Combining angle-resolved photoemission spectroscopy (ARPES) measurement and density-functional theory simulation, we report the observations of two-dimensional quantum well states due to the confinement of bulk electron pocket and Dirac cone to the nearly isolated surface layer. The theoretical calculations on the slab model also suggest that the ARPES observed spectra are almost entirely contributed by the top two layers. Our results not only explain the disagreement of band structures between the recent experiments and calculations, but also suggest an equally important role played by quantum confinement, together with strong correlation and band topology, in shaping the electronic properties of this material.

Kagome materials are a class of material with a lattice structure composed of corner-sharing triangles that produce various exotic electronic phenomena, such as Dirac fermions, van Hove singularities, and flat bands. However, most of the known kagome materials have a flat band detached from the Fermi energy, which limits the investigation of the emergent flat band physics. In this work, by combining soft x-ray angle-resolved photoemission spectroscopy (ARPES) and the first-principles calculations, the electronic structure is investigated of a novel kagome metal CeNi5 with a clear dispersion along the kz direction and a Fermi level flat band in the Gamma-K-M-Gamma plane. Besides, resonant ARPES experimental results indicate that the valence state of Ce ions is close to 4(+), which is consistent with the transport measurement result. Our results demonstrate the unique electronic properties of CeNi5 as a new kagome metal and provide an ideal platform for exploring the flat band physics and the interactions between different types of flat bands by tuning the valence state of Ce ions.

Exchange bias (EB) is a cornerstone of modern magnetic memory and sensing technologies. Its extension to the realm of two-dimensional (2D) van der Waals (vdW) magnets holds promise for revolutionary advancements in miniaturized and efficient atomic spintronic devices. However, the blocking temperature of EB in 2D vdW magnets is currently well below room temperature  130 K. This study reports a robust EB phenomenon in Fe3GaTe2 thin-layer devices, which significantly increases the blocking temperature to a near-room-temperature record of 280 K. Both the bias direction and magnitude can be isothermally tuned by adjusting the field sweep range, in striking contrast to the conventional EB in ferromagnetic/antiferromagnetic (FM/AFM) bilayers. We propose an exchange spring model in which crystal defects with higher coercivity act as the pivotal pinning source for the observed EB phenomenon, deviating from the conventional FM/AFM interface mechanism. Cumulative growth of minor loops and multiple magnetization reversal paths are observed in field cycles below the saturation field, consistent with the hard FM defects behavior of our exchange spring model. These findings provide insights into the complex magnetic order in 2D ferromagnets and open new avenues for developing practical ultrathin vdW spintronic devices with EB-like properties at room temperature.

In quantum many-body systems, particularly, the ones with large near-EF density states, like flat bands or van Hove singularity (VHS), electron correlations often give rise to rich phase diagrams with multiple coexisting/competing orders occurring at similar energy scales. The recently discovered locally noncentrosymmetric heavy fermion superconductor CeRh2As2 has stimulated extensive attention due to its unusual H-T phase diagram, consisting of two-phase superconductivity, antiferromagnetic order, and possible quadrupole-density wave orders. However, despite its great importance, the near-EF electronic structure remains experimentally elusive. Here, we provide this key information by combining soft X-ray and vacuum ultraviolet (VUV) angle-resolved photoemission spectroscopy measurements and atom-resolved DFT+U calculations. With bulk-sensitive soft X-rays, we reveal quasi-2D hole- and 3D electron- pockets with a pronounced nesting feature. Most importantly, we observe a symmetry-protected fourfold VHS coexisting with the Ce 4f flat bands near the EF, which, to the best of our knowledge, has never been reported before. Such a rare coexistence is expected to lead to a large density of states at the zone edge, enhancement in electron correlations, and a large upper critical field of the odd-parity superconducting phase. Uniquely, it will also result in a new type of f-VHS hybridization that alters the order and fine electronic structure of the symmetry-protected VHS and flat bands. These peculiarities offer important dimensions for understanding the reported rich phase diagram and are discussed as an origin of superconductivity with two phases. Our findings not only provide key insights into the nature of multiple phases in CeRh$_2$As$_2$, but also open up new prospects for exploring the novelties of many-body systems with f-VHS hybridization.

Superconducting diode effect (SDE) with nonreciprocal supercurrent transport has attracted intense attention recently, not only for its intriguing physics, but also for its great application potential in superconducting circuits. It is revealed in this work that planar Josephson junctions (JJs) based on type-II Weyl semimetal (WSM) MoTe$_2$ can exhibit a prominent SDE due to the emergence of asymmetric Josephson effect (AJE) in perpendicular magnetic fields. The AJE manifests itself in a very large asymmetry in the critical supercurrents with respect to the current direction. The sign of this asymmetry can also be effectively modulated by the external magnetic field. Considering the special noncentrosymmetric crystal symmetry of MoTe$_2$, this AJE is understood in terms of the Edelstein effect, which induces a nontrivial phase shift in the current phase relation of the junctions. Besides these, it is further demonstrated that the rectification of supercurrent in such MoTe$_2$ JJs with the rectification efficiency up to 50.4%, unveiling the great application potential of WSMs in superconducting electronics.

Electronic orders such as charge density wave (CDW) and superconductivity raise exotic physics and phenomena as evidenced in recently discovered kagome superconductors and transition metal chalcogenides. In most materials, CDW induces a weak, perturbative effect, manifested as shadow bands, minigaps, resistivity kinks, etc. Here we demonstrate a unique example-transition metal tetratellurides TaTe_{4}, in which the CDW order dominates the electronic structure and transport properties. Using angle-resolved photoemission spectroscopy, we found that the band structure of CDW TaTe_{4} is characterized by small, bulk electron pockets. Density functional theory analyses reveal their CDW origin from the folding of the original, large Fermi pockets. Importantly, the CDW induced pockets result in prominent frequencies in the quantum oscillation of the magnetoresistance. Satisfactory agreements are reached between results from photoemission spectroscopy, density functional theory, and quantum oscillation, concerning the shape, size, location, and angle dependence of the CDW pockets. Our results underline transition metal tetratellurides as an outstanding example for exploring the interplay between CDW, pressure induced superconductivity, and potential topological states under strong field.

The vacancy effect in quantum spin liquid (QSL) has been extensively studied. A finite density of random vacancies in the Kitaev model can lead to a pileup of low-energy density of states (DOS), which is generally experimentally determined by a scaling behavior of thermodynamic or magnetization quantities. Here, we report detailed muon spin relaxation (μSR) results of H 3 LiIr 2 O 6 , a Kitaev QSL candidate with vacancies. The absence of magnetic order is confirmed down to 80 mK, and the dynamical spin fluctuations are found to be persistent at low temperatures. Intriguingly, the time-field scaling law of longitudinal-field μSR polarization is observed with the critical exponent of 0.46, exhibiting excellent consistency with scaling behavior of specific heat and magnetization data. This points to the finite DOS with the form of N(E) ~ E ν , wihch is expected for the Kitaev QSL in the presence of vacanncies.

In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral“Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU（2） symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb3S6. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb3S6, paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.