Grain boundaries are critical for determining the functionality of polycrystalline materials. Here we investigate and present the structural and transport properties of grain boundaries in the unconventional superconductor CeCoIn5. We provide a detailed recipe for the fabrication of isolated grain-boundary devices from as-grown polycrystalline samples of CeCoIn5. Electron backscattered diffraction imaging of polycrystalline CeCoIn5 samples reveals an abundance of 90 degrees misorientation grain boundaries, suggesting a preferential nucleation of CeCoIn5 grains with 90 degrees misorientation over a random distribution of grain orientations. Transport measurements across grain-boundary devices establish coherence of superconductivity and allow us to establish a lower bound on the critical current density for the grain boundaries. Our work opens possibilities for fabrication of quantum devices such as Josephson junctions out of bulk unconventional superconducting materials.

The discovery of local-moment magnetism in van der Waals (vdW) semiconductors down to the single-layer limit has led to a paradigm shift in the understanding of two-dimensional (2D) magnets. The incorporation of strong electronic and magnetic correlations in 2D vdW metals remains a sought-after platform to enable control of emergent quantum phases and to achieve more theoretically tractable microscopic models of complex materials. To date, however, there is limited success in the discovery of such metallic vdW platforms, and f-electron monolayers remain out of reach. Here, we demonstrate that strongly correlated β-uranium tritelluride (β-UTe3) can be exfoliated to the monolayer limit. Unexpectedly, β-UTe3 remains ferromagnetic in this limit with an enhanced ordering temperature of 35 kelvin, a factor of two larger than its bulk counterpart. Our work establishes β-UTe3 as a materials platform for investigating and modeling correlated behavior in the monolayer limit and opens numerous avenues for quantum control with, e.g., strain engineering.

Metals typically have multiple Fermi surface sheets, and when they enter the superconducting state, some electrons on these sheets may remain uncondensed, or their superconducting pairs can be rapidly destroyed by a magnetic field. Detecting uncondensed electrons within the superconducting state provides key information about the underlying electronic structure; however, this task remains a significant experimental challenge. Here we demonstrate quantum oscillations from the uncondensed electrons in the heavy-fermion superconductor CeCoIn5, observed through thermal conductivity measurements with a magnetic field rotating within the tetragonal a-b plane. We detect a fine structure in thermal conductivity, characterized by multiple small resonances (oscillations) in a rotating magnetic field. Remarkably, the phase of these resonances shifted by as much as π for a field above 9.7 T where spin-density wave (SDW) order emerges and coexists with superconductivity. This phase shift is naturally explained by a change in the Berry phase of the uncondensed Fermi surface, driven by the Fermi surface reconstruction associated with the onset of SDW order. Our work unambiguously shows the existence of uncondensed electrons in the superconducting state of CeCoIn5, thus resolving a longstanding debate on this issue.

The intersection between nonsymmorphic symmetry and electronic correlations has emerged as a platform for topological Kondo semimetallic states and unconventional spin textures. Here, we report the synthesis of nonsymmorphic UPd0.65Bi2 single crystals and their structural, electronic, magnetic, and thermodynamic properties. UPd0.65Bi2 orders antiferromagnetically (AFM) below TN 161 K as evidenced by a sharp cusp in magnetic susceptibility, a second-order phase transition in specific heat, and an upturn in electrical resistivity, which suggests an incommensurate AFM structure that deviates from the A-type magnetism typically observed in this class of materials. Across TN, Hall effect measurements reveal a change from electron-dominated to hole-dominated transport, which points to a sharp reconstruction in the electronic structure at TN. Upon further cooling, a first-order transition is observed at T1 30 K in magnetic susceptibility and heat capacity but not in electrical resistivity or Hall measurements, which indicates a small change in the AFM structure that does not affect the electronic structure. Our specific heat data reveal a small Sommerfeld coefficient (gamma 13 mJmol-1K-2), consistent with localized 5 f electrons. Our results indicate that UPd0.65Bi2 hosts weak electronic correlations and is likely away from a Kondo semimetallic state. Low-temperature magnetization measurements show that the AFM structure is remarkably stable to 160 kOe and does not undergo any field-induced transitions. Neutron diffraction and magnetization experiments at higher fields would be valuable to probe the presence of unconventional spin textures.

We report 73Ge nuclear quadrupole resonance (NQR) and magnetic resonance (NMR) spectroscopy in the heavy-fermion quantum-critical ferromagnet CeRh6Ge4. NQR and NMR spectral measurements at the two nonequivalent Ge sites reveal electric field gradient tensors and the directions of their principal axes relative to the hexagonal basal plane. The spin-lattice relaxation rate 1/T1 experiments reveal a clear critical slowing down approaching the ferromagnetic transition. 1/T1 in the paramagnetic state is found to be predominantly caused by fluctuating 4f-local moments. The Knight shift shows Curie-Weiss behavior at high temperature and a deviation from this below T & lowast; 25 K possibly due to a mixture of crystalline electric field effects and Kondo screening. Order-parameter-like behavior of hyperfine fields at the Ge sites and ferromagnetic signal enhancement are observed in Zeeman-perturbed NQR, with uniform ferromagnetic order and a small ordered moment of 0.26 mu B/Ce confined within the ab plane. The ordered moment shows a notable in-plane magnetic stiffness against out-of-plane radio-frequency fields and has an (XY-type) in-plane isotropic nature. Our results reveal a strong easy-plane anisotropy of 4f-electron moment and suggest an involved interplay of hybridization and local moment physics in this quantum critical heavy-fermion ferromagnet.

We report temperature dependent X-Band (nu approximate to 9.5 GHz) Electron Spin Resonance (ESR) on the GdCuBi2 intermetallic compound. This compound presents a metallic Curie-Weiss paramagnetic behavior at high temperatures and orders antiferromagnetically at T-N = 14.3 K. Well above T-N (T > 250 K), the ESR experiments revealed temperature independent g-values spectra composed of a single Dysonian Gd3+ ESR line for the studied compound. Within the same temperature range, the Gd3+ ESR linewidth Delta H presents a linear broadening temperature dependence known as Korringa behavior. The obtained Korringa rate (Delta H/Delta T) and g-shift (Delta g) from the ESR measurements, along with the study of the macroscopic properties of GdCuBi2 (e.g. specific heat data and magnetic susceptibility) made it possible to explore Gd3+ spin dynamics in this system based on evaluation of the exchange parameters between the Gd3+ ESR probes and the conduction-electrons (ce) in this compound. Our results indicate that the exchange bottleneck effects and a q-dependent exchange interaction (J(fs)(q)) between the Gd(3+)4f and the ce are likely to be present in GdCuBi2. Disregarding the bottleneck effects in the simplest approximation, we extract the exchange parameters J(fs)(q=0) approximate to 380 meV and (1/2)approximate to 3.0 meV for the Gd3+ spin dynamics in GdCuBi2. These values of J(fs)(q) and (1/2) are typical of Gd3+ local moments in intermetallic materials and the small ratio [/J(fs)(2)(0)] approximate to 0.008 suggests a strongly anisotropic (or quasi-2D) Fermi surface for GdCuBi2.

Excitonic insulators are electronically-driven phases of matter characterized by the spontaneous condensation of electron-hole pairs. Here we show that La_3Cd_2As_6 undergoes a transition at T_0=278 K to a highly insulating state with no accompanying structural transition. We observe quasi-two-dimensional electrical transport and charge fluctuations consistent with an electronic transition enabled by enhanced Coulomb interactions. Density functional theory calculations are unable to replicate the insulating ground state. Our results support the opening of a gap by excitonic effects at T_0, placing La_3Cd_2As_6 as a rare example of a bulk excitonic insulator.

The electrical conductivity of nanolayered copper/niobium composites fabricated using accumulative roll bonding was investigated as a function of layer thickness. Cu/Nb was used as a model system to evaluate the processing-structure–property relationship stemming from the accumulative roll bonding process. The physical properties were compared against samples of individual average layer heights ranging from 193 to 25 nm. The electrical resistivity was measured over a temperature range of ∼3–300 K. Analysis on the role of interfaces on temperature dependence is conducted including the residual resistivity ratio and temperature coefficient of resistivity. It was found that electrical resistivity increases with decreasing layer height.

We present time-domain THz spectroscopy of thin films of the heavy-fermion superconductor CeCoIn5. Below the approximate to 40 K Kondo coherence temperature, a narrow Drude-like peak forms, as a result of the forbital-conduction-electron hybridization and the formation of the heavy-fermion state. The complex optical conductivity is analyzed through a Drude model and extended Drude model analysis. Via the extended Drude model analysis, we measure the frequency-dependent scattering rate (1/tau) and effective mass (m*/mb). This scattering rate shows a linear dependence on temperature, which matches the dependence of the resistivity as expected. Nevertheless, the width of the low-frequency Drude peak itself that is set by the renormalized quasi-particle scattering rate (1/tau* = mb/m*tau) shows a T2 dependence. This is the scattering rate that characterizes the relaxation time of the renormalized quasiparticles. This gives evidence for a Fermi liquid state, which in conventional transport experiments is hidden by the strong temperature dependent mass.

In magnetic topological materials, time-reversal symmetry breaking gives rise to topological point and line nodes with distinctive signatures in the anomalous Hall and anomalous Nernst conductivity that satisfy the well-known Mott relation. However, this relationship can fail for doping-dependent transport measurements of materials with complex magnetism, topology, and electronic correlations. In this work, we present transport measurements of the correlated topological metal UCoAl doped with Ru, which appear to violate the Mott relation. We develop a model that captures the evolution of Stoner magnetism and topological Weyl points as a function of doping. Using this model, we show how the correlated flat band in this material pins the Weyl points to the Fermi energy, and demonstrate how this explains the unusual doping-dependent behavior of the anomalous Hall and anomalous Nernst conductivities in this material, while the Mott relation is in fact satisfied at each doping level.

We present a combined theoretical and experimental study on the optical conductivity of CeIr3B2, where quasione-dimensional Ce chains form along the c axis of the monoclinic crystal. Significant hybridization-induced features are observed along the Ce chains by broadband infrared spectroscopy, demonstrating mixed-valent behavior over a wide range of temperatures (6-300 K) and energies (up to 0.8 eV). The ferromagnetic transition at 41 K had no noticeable influence on the temperature evolution of the optical conductivity. A comparison with density functional theory plus dynamic mean-field theory calculations demonstrates the quasi-one-dimensional nature of CeIr3B2 and the local character of the interactions responsible for the electronic renormalization. Furthermore, we demonstrate how the spectroscopic signatures of this mixed-valent compound are captured by theory, providing a clear distinction from the response expected in the integer-valent Kondo regime.

Plutonium-based correlated electron materials host exotic physical phenomena ranging from unconventional heavy-fermion superconductivity to topological Kondo insulating states. Self-irradiation damage can influence many properties of such radioactive materials. Structural disorder effects due to alpha radiation have been frequently studied using techniques such as transport, thermodynamics, and x-ray diffraction. Here, we use 239Pu nuclear magnetic resonance (NMR) to study the long-term influence of self-damage on the lattice and local electronic structures in a single crystal of the candidate topological insulator plutonium tetraboride (PuB4). We first characterize the anisotropy of the 239Pu resonance and confirm the local axial-site symmetry inferred from previous polycrystalline measurements. Aging effects are then evaluated over the time frame of six years. We find that, though the static 239Pu NMR spectra show a slight modulation in their shape, their field-rotation pattern reveals no change in 239Pu local site symmetry over time, suggesting that aging has a surprisingly small impact on the spatial distribution of the static hyperfine field. Further, ligand-site 11B NMR finds little time-dependent change in the size of electric field gradient around 11B sites. By contrast, aging has a prominent impact on the 239Pu NMR relaxation processes and signal intensity. Specifically, aging-induced damage manifests itself as an increase in the spin-lattice relaxation time T1, an increased distribution of T1, and a signal intensity that decreases linearly by 20% per year. An effective spin-spin relaxation time T2, eff in the aged sample shortens drastically towards lower temperature, suggesting growth of slow fluctuations of the hyperfine field that are linked to radiation-damage-induced inhomogeneity. Our NMR study sheds light on the interplay of radiation damage and local magnetic interactions in correlated insulators.

We study the Hall effect, AC magnetic susceptibility ( χ ac ), and magnetic force microscopy of the uniaxial ferromagnet CeRu 2 Ga 2 B with a centrosymmetric crystal structure. We observe a finite topological Hall effect (THE) within the ordered phase, before the magnetization is polarized by applied field. By comparing the field dependences of the area fraction of the magnetic bubbles, the derivative of χ ac , and the THE signal, we deduce that the magnetic bubbles in CeRu 2 Ga 2 B evolve from the trivial to topological spin texture with field. Our findings enable the expansion of the search for magnetic materials hosting topological spin textures to include uniaxial ferromagnets and open a new possibility to tailor the topological spin texture.

We report the synthesis and physical properties of the new compound YNiSn_2, which crystallizes in the orthorhombic Cmcm structure. The material exhibits semimetallic behavior and develops a giant positive magnetoresistance approaching 1200% at B = 16 T. Pronounced de Haas-van Alphen and Shubnikov-de Haas oscillations reveal a dominant quasi-two-dimensional Fermi surface with an exceptionally small cyclotron effective mass of m^* = 0.08 m0, indicating light carriers and a tiny Fermi surface pocket. The strong anisotropy revealed by Shubnikov-de Haas quantum oscillation measurements highlights the low-dimensional electronic character of YNiSn_2, positioning it as a promising Dirac semimetal candidate.

The interplay between superconductivity and magnetism has been a subject of significant interest for decades. While extensive research has focused on modifying the superconducting state through a magnetic domain as an independent variable, the manipulation of magnetic domains by the superconducting state has been relatively unexplored, primarily due to their higher stiffness compared to the energy associated with superconducting vortices. In this Letter, we demonstrate the manipulation of magnetic domains by thermally activated superconducting vortices in a ferromagnet/superconductor hybrid. We observe a reversible domain transition between metastable magnetic stripes and bubbles in a Nb/CeRu2Ga2B hybrid induced by vortex motion and the trapped field within the Nb superconducting film. The comparable Curie and superconducting critical temperatures and the presence of magnetic metastable states enable the magnetic domain changes driven by superconducting vortices in this hybrid system.

We study the magnetic heat capacity of a series of magnetically ordered Ce-based heavy-fermion materials, which show an anomalous T3 heat capacity in excess of the phonon contribution in many materials. For compounds for which magnon models have been worked out, we show that the local-moment magnon heat capacity derived from the measured magnon spectra underestimates the experimental specific heat. The excess heat capacity reveals increasing density of states with increasing energy, akin to a pseudogap. We show that this anomalous temperature-dependent term is not associated with proximity to a quantum critical point, but is strongly correlated with TN, indicating the anomalous excitations are governed by the magnetic exchange interaction. This insight may hold key information for understanding magnetically ordered heavy fermions.

The optical conductivity sigma(omega, T) of CeRhSn was studied by broadband infrared spectroscopy. Temperaturedependent spectral weight transfer occurs over high energy (0.8 eV) and temperature (similar to 500 K) scales, classifying CeRhSn as a mixed-valent compound. The optical conductivity reveals a substantial anisotropy in the electronic structure. Renormalization of sigma(omega, T) occurs as a function of temperature to a coherent Kondo state with concomitant effective mass generation. Associated spectroscopic signatures were reproduced remarkably well by the combination of density functional theory and dynamical mean-field theory using a momentum-independent self-energy. The theory shows that the anisotropy for energies >10 meV is mainly driven by the bare three-dimensional electronic structure that is renormalized by local electronic correlations. The possible influence of magnetic frustration and quantum criticality is restricted to lower energies.

By utilizing a multi-orbital periodic Anderson model with parameters obtained from ab initio band structure calculations, combined with degenerate perturbation theory, we derive effective Kondo-Heisenberg and spin Hamiltonians that capture the interaction among the effective magnetic moments. This derivation encompasses fluctuations via both nonmagnetic 4f^0 and magnetic 4f^2 virtual states, and its accuracy is confirmed through comparison with experimental data obtained from CeIn_3. The significant agreement observed between experimental results and theoretical predictions underscores the potential of deriving minimal models from first-principles calculations for achieving a quantitative description of 4f materials. Moreover, our microscopic derivation unveils the underlying origin of anisotropy in the exchange interaction between Kramers doublets, shedding light on the conditions under which this anisotropy may be weak compared to the isotropic contribution.

Controlled charge flows are fundamental to many areas of science and technology, serving as carriers of energy and information, as probes of material properties and dynamics, and as a means of revealing or even inducing broken symmetries. Emerging methods for light-based current control offer promising routes beyond the speed and adaptability limitations of conventional voltage-driven systems. However, optical generation and manipulation of currents at nanometer spatial scales remains a basic challenge and a crucial step towards scalable optoelectronic systems for microelectronics and information science. Here, we introduce vectorial optoelectronic metasurfaces in which ultrafast light pulses induce local directional charge flows around symmetry-broken plasmonic nanostructures, with tunable responses and arbitrary patterning down to sub-diffractive nanometer scales. Local symmetries and vectorial current distributions are revealed by polarization- and wavelength-sensitive electrical readout and terahertz (THz) emission, while spatially-tailored global currents are demonstrated in the direct generation of elusive broadband THz vector beams. We show that in graphene, a detailed interplay between electrodynamic, thermodynamic, and hydrodynamic degrees of freedom gives rise to rapidly-evolving nanoscale driving forces and charge flows under extreme temporal and spatial confinement. These results set the stage for versatile patterning and optical control over nanoscale currents in materials diagnostics, THz spectroscopies, nano-magnetism, and ultrafast information processing.

The thermal conductivity of heavy-fermion superconductor CeCoIn$_5$ was measured with a magnetic field rotating in the tetragonal a-b plane, with the heat current in the anti-nodal direction, $J$ || [100]. We observe a sharp resonance in thermal conductivity for the magnetic field at an angle $\theta$ $\sim$ 12$^{\circ}$, measured from the heat current direction [100]. This resonance corresponds to the reported resonance at an angle $\theta'$ $\sim$ 33$^{\circ}$ from the direction of the heat current applied along the nodal direction, $J$ || [110]. Both resonances, therefore, occur when the magnetic field is applied in the same crystallographic orientation in the two experiments, regardless of the direction of the heat current, proving conclusively that these resonances are due to the structure of the Fermi surface of CeCoIn$_5$. We argue that the uncondensed Landau quasiparticles, emerging with field, are responsible for the observed resonance. We support our experimental results with density-functional-theory model calculations of the density of states in a rotating magnetic field. Our calculations, using a model Fermi surface of CeCoIn$_5$, reveal several sharp peaks as a function of the field direction. Our study demonstrates that the thermal-conductivity measurement in rotating magnetic field can probe the normal parts of the Fermi surface deep inside the superconducting state.