The discovery of pressure-induced high temperature superconductivity in the bilayer nickelate La_3Ni_2O_7 has raised the question of how its spin-density-wave (SDW) state evolves toward the superconducting regime. Here, we report a systematic electronic Raman study of La_3Ni_2O_7 single crystals under hydrostatic pressures up to 16.51 GPa. Both the SDW gap energy and the transition temperature T_SDW show an overall increase with pressure, while the dimensionless coupling ratio 2Δ_SDW/(k_BT_SDW) remains constant around ∼7.5, indicating a robust strong-coupling character of SDW state. At the same time, the Raman SDW peak broadens as pressure is applied, indicating a gradual weakening of long-range SDW order. These results reveal an unusual pressure evolution in which the SDW energy scale is enhanced while the SDW state becomes progressively less coherent, providing spectroscopic constraints on the magnetic correlations relevant to superconductivity in bilayer nickelates.

We study the ab-plane and c-axis charge dynamics of La_{4}Ni_{3}O_{10} using optical spectroscopy. While a pronounced Drude profile, i.e., metallic response, is observed in the ab-plane optical conductivity σ_{1}^{ab}(ω), the c-axis optical spectra σ_{1}^{c}(ω) exhibit semiconducting behavior. The zero-frequency extrapolation of the optical conductivity σ_{1}(ω→0)≡1/ρ_{dc} leads to a resistivity anisotropy ρ_{c}/ρ_{ab} exceeding 1000 at low temperatures, which is much larger than the values in iron-based superconductors but comparable to those in high-T_{c} cuprates. The interband response is also highly anisotropic, showing salient orbital selectivity for light polarized in the ab plane and along the c axis. The interband-transition peaks in both σ_{1}^{ab}(ω) and σ_{1}^{c}(ω) are located at lower energies compared to density-functional-theory predictions, signifying considerable electronic correlations. By investigating the spectral weight transfer, we find that above the density-wave transition, Coulomb correlations have a marked impact on the charge dynamics of La_{4}Ni_{3}O_{10}, whereas in the density-wave state, a gap opens with the Ni-d_{z^{2}} orbital being involved.

Motivated by the discovery of superconductivity in bilayer La3Ni2O7 at 80 K and the increased superconducting transition temperature, Tc, up to 96 K in single crystals of La1.57Sm1.43Ni2O7-delta under pressure, we systematically study the effect of Sm substitution on the superconductivity and structure of La3-xSmxNi2O7 (0 x 1.5) under pressure. Experimental investigations in polycrystalline samples reveal that Sm substitution monotonically decreases the lattice constants c and a, thereby enhancing crystal structural distortion and leading to an evolution of the metallic ground state in La3Ni2O7 to an insulating state in La1.5Sm1.5Ni2O7. The optimal Tonset c rises with increasing Sm substitution, and the maximum Tonset c is 89.2 K in polycrystalline La1.5Sm1.5Ni2O7. Divergences in Tc compared with single crystals of La1.57Sm1.43Ni2O7-delta are likely due to variations in the microstructure induced by different material growth approaches. Our results suggest that the enhancement of Tc in La3-xSmxNi2O7 is mainly affected by the compressed c lattice before saturation, and the superconducting transition pressure increases with substitution concentration. Our experimental results provide insight into the influence of small-radius rare-earth element substitution on nickelate superconductors, offering a means to further increase the transition temperature.

The physical properties of BaCoTe2O7 single crystals were investigated using magnetization, magnetostriction, electron spin resonance, and electric polarization under static and pulsed high magnetic fields. Experimental results reveal that single-crystal sample is an antiferromagnet at low temperatures, with an effective pseudospin Seff of 1/2 and a relatively large anisotropic effective g factor, which originates from the lowest Kramers doublet of Co2+ with dominant |Sz| = 3/2 character under strong spin-orbit coupling. When a magnetic field is applied along the easy magnetization c axis, two successive magnetic phase transitions (Hc1 and Hc2) were observed, between the two critical fields, the Co ions with a TTT4. spin configuration correspond to a 1/2 magnetization plateau. At critical field Hc1, spins rotate from parallel (antiparallel) to nearly perpendicular to the magnetic field, at Hc2, a change occurs from a ferrimagnetic state to a high-field coplanar spin configuration. Magnetostriction measurements indicate significant anisotropic spin-lattice coupling in BaCoTe2O7. First-principles calculations based on the four-state method reveal comparable antiferromagnetic nearest-neighbor and next-nearest-neighbor exchange interactions (JNN = -10.76 meV and JNNN = -9.33 meV), which imply strong competing interactions and exchange frustration in the zigzag Co network of BaCoTe2O7. The exchange interactions between the Co & centerdot; & centerdot; & centerdot; Co bonds in the noncollinear spin configuration (with a canted TT4.4. spin arrangement) induced by the magnetic field give rise to inequivalent exchange coupling, resulting in the emergence of net electric dipole moments. Through analysis of the multistep transitions induced by pulsed magnetic fields in the block-ordered antiferromagnetic state, combined with magnetostriction and polarization measurements, and supported by the large exchange energy scale relative to the N & eacute;el temperature, the multiferroic behavior of BaCoTe2O7 can be understood in terms of an exchange striction mechanism associated with its noncollinear spin order.

We successfully prepared an A-site-ordered quadruple perovskite oxide CeCu3Fe2Ru2O12 by using a high-pressure method (10 GPa, 1400 K). The compound crystallizes in the Im3 & strns; space group, with A-site ordering of Ce and Cu ions in a ratio of 1:3, but B-site disordered distribution of Fe and Ru ions. Bond-value-sum calculations and x-ray photoelectron spectroscopy measurement manifest that the charge distribution is Ce3.5+Cu32+Fe23+Ru24.25+O12 . A ferrimagnetic phase transition occurs at TC = 73.6 K followed by a spin glass behavior at 50.3 K consistent with the conventional dynamical scaling power law. Electrical transport measurement shows that the intrinsic electrical behavior is semiconducting and the resistivity obey the adiabatic small-polaron model. The specific heat follows a T2 law instead of traditional phonon-dominated T3 behavior implying a finite energy gap in the excitation spectrum.

The discovery of superconductivity in Ruddlesden-Popper nickelates has established a new frontier in the study of high-temperature superconductors. However, the underlying pairing mechanism and its relationship to the material's electronic and magnetic ground states remain elusive. Since unconventional superconductivity often emerges from a complex interplay of magnetic correlations, elucidating the magnetic ground state of the nickelates at ambient pressure is crucial for understanding the emergence of superconductivity under high pressure. Here, we combine high-resolution angle-resolved photoemission spectroscopy with tight-binding model simulation to investigate the electronic structure of the representative trilayer Ruddlesden-Popper nickelate La_4Ni_3O_10. We provide the first experimental evidence of band splitting induced by interlayer coupling and further resolve the momentum-dependent density wave gap structures along all the Fermi surfaces. Our findings identify the mirror-selective Fermi surface nesting as the origin of the interlayer antiferromagnetic spin density wave and demonstrate the dominant role of Ni-3d_z^2 orbitals in the low-energy physics of La_4Ni_3O_10. These results provide a fundamental framework for understanding the magnetic interactions and high-temperature superconductivity mechanism in the Ruddlesden-Popper nickelate family.

The recent discovery of high-Tc superconductivity in Ruddlesden-Popper (RP) nickelates has motivated extensive efforts to explore higher-Tc superconductors. Here, we systematically investigate Nd-doped La3Ni2O7 using density functional theory (DFT) and renormalized mean-field theory (RMFT). DFT calculations reveal that both the lattice constants and interlayer spacing decrease upon Nd substitution, similar to the effect of physical pressure. However, the in-plane Ni-O-Ni bond angle evolves non-monotonically with doping, increasing to a maximum at 70 d_z^2 orbital, demonstrating an orbital-dependent effect of rare-earth substitution. Through the bilayer two-orbital t-J model, RMFT analysis further shows an s±-wave pairing symmetry, with Tc rising to a maximum at about 70 d_z^2 orbital hopping and a gradual decrease in electron density. These results highlight the delicate interplay among structural tuning, orbital hybridization, and superconductivity, providing important clues to design higher-Tc RP nickelate superconductors.

High-temperature (HT) kagome magnets provide important platforms to explore nontrivial topological physics and promising potentials for spintronic applications, due to the complicated interactions among their electrons, lattices, and magnetism. Herein, the nontrivial electronic properties of a HT layered kagome-magnet, HoMn6Sn6, are systematically resolved by quantum oscillation measurements and density functional theory (DFT) calculations. The prominent Shubnikov-de Haas (SdH) oscillations under pulsed high magnetic fields reveal a high quantum mobility of 0.37 m2·V-1·s-1 for this HT ferrimagnet. The observed multiple-frequency quantum oscillations exhibit various angular dependences, consistent with DFT calculations which suggest a complex Fermi topology of three three-dimensional hole pockets and two electron pockets. The observed π shift of the Berry phase for quantum oscillations unveils nontrivial topological properties in HoMn6Sn6, further confirmed by DFT calculated Dirac fermions and large anomalous Hall conductivity. Our findings establish HoMn6Sn6 as an HT magnetic candidate for topological magnetoelectronics or spin quantum applications.

High-T_{c} superconductivity has recently been discovered in Ruddlesden-Popper (RP)-phase nickelates under pressure, where the low-energy electronic structure is dominated by Ni d_{x^{2}−y^{2}} and d_{z^{2}} orbitals. However, the respective roles of these orbitals in superconductivity remain unclear. Here, by combining x-ray absorption, electron energy loss spectroscopy, and density functional theory calculations on La_{4}Ni_{3}O_{10} single crystals, we identify ligand holes in the p_{x,y} orbitals of planar oxygen and the p_{z} orbitals of apical oxygen, which hybridize with the Ni d_{x^{2}−y^{2}} and d_{z^{2}} orbitals, respectively. These ligand holes enable orbital-selective O K-edge resonant inelastic x-ray scattering (RIXS) study, which reveals that d_{x^{2}−y^{2}} states dominate the low-energy charge excitations and are more itinerant. We also observe an ∼0.1eV bimagnon through RIXS and Raman spectroscopy. Our results reveal distinct contributions of Ni d_{x^{2}−y^{2}} and d_{z^{2}} orbitals to the electronic and magnetic structure and provide direct experimental insights to understand the RP-phase nickelate superconductors.

Ultrahigh energy storage capability and breakdown field strength are key factors for next-generation pulsed power dielectric capacitors. Here, rare-earth element Nd-doped Ba2Bi4Ti5O18 thin film capacitors were prepared on Pt/Ti/SiO2/Si substrates by chemical solution deposition. Nd doping can refine the grain size and reduce the leakage current, leading to an enhanced breakdown field strength. Furthermore, it effectively suppresses the dielectric loss and strengthens the relaxor characteristics. Consequently, the Ba2Bi3.875Nd0.125Ti5O18 thin film achieves a high energy storage density of 118.1 J/cm3 and a high efficiency of 95.0%, and derives an ultrahigh comprehensive energy storage figure of merit of 2362 J/cm3. Meanwhile, it exhibits excellent fatigue endurance up to 106 cycles, and outstanding energy storage stability over a wide temperature range from 10 degrees C to 200 degrees C. These results indicate that Nd doping is an effective approach to enhance the energy storage performance of Ba2Bi4Ti5O18 thin films.

We report a polarized ultrafast pump-probe study of the normal-state electronic dynamics in bilayer La_3Ni_2O_7 and trilayer La_4Ni_3O_10 single crystals at ambient pressure. While both nickelates exhibit density-wave (DW) transitions accompanied by the opening of a quasiparticle relaxation bottleneck, their electronic responses display strikingly different symmetry properties. La_4Ni_3O_10 maintains an isotropic optical response across the entire temperature range. In contrast, La_3Ni_2O_7 exhibits a pronounced twofold (C_2) anisotropy in its low-temperature electronic dynamics. This electronic nematicity, evident in both the relaxation dynamics and the effective gap scales, competes with a secondary isotropic order emerging below 115 K. The presence of macroscopic electronic anisotropy in the bilayer system, and its absence in the trilayer system, suggests an intimate relation between electronic nematic fluctuations and superconducting pairing in La_3Ni_2O_7 that worth for deeper explorations.

The synthesis of high-quality Ruddlesden-Popper (RP) nickelates remains challenging due to variations in oxygen content and the prevalence of intergrown RP phases. Precisely controlling the stoichiometry and characterizing the resulting physical properties are essential for understanding the mechanism of high-T_c superconductivity in these materials. In this work, we synthesize a series of La_3Ni_2O_7+δ samples with systematically controlled oxygen content and perform comprehensive structural and compositional analyses. Precise oxygen tuning enables us to tailor the microstructure, yielding a pure bilayer phase, a mixture of bilayer and hybrid single-layer-bilayer phases, and a predominantly bilayer phase containing trilayer intergrowths. High-pressure transport measurements reveal distinct superconducting transitions with contrasting T_c values, corresponding to the bilayer phase, the hybrid phase, and trilayer inclusions. Notably, we find that oxygen content not only governs the phase purity-i.e., the presence of intergrowth phases-but also directly modulates the upper critical field (H_c2) of the bilayer superconductivity. By establishing a phase diagram of T_c and H_c2 as functions of oxygen content in La_3Ni_2O_7+δ, this work advances synthetic control and provides new insights into the superconducting mechanism of RP nickelates.

Rare-earth triangular lattices provide an ideal platform for exploring novel quantum magnetic states. Here, we report the crystal growth and magnetic properties of a rare-earth triangular-lattice compound, ErZn3P3. Alternating-current magnetic susceptibility and specific heat measurements reveal a long-range antiferromagnetic order below T = 0.12 K. The long-range magnetic order can be rapidly suppressed by a small magnetic field of & micro;0H = 0.04 T along the c axis, followed by a broad field-induced anomaly above 0.05 T that shifts to higher temperatures as the magnetic field increases. The magnetic entropy release below 2 K is estimated to be 0.852(42)R ln 2, which is consistent with a Kramers doublet described by an effective spin S = 1/2. Finally, a magnetic field-temperature contour map is constructed based on the specific heat results. Our work identifies a long-range yet fragile magnetic order in this newly grown S = 1/2 quantum magnet, and its fragility suggests the presence of strong quantum fluctuations arising from geometric frustrations and quantum spins in ErZn3P3.

The full-Heusler intermetallic compound ScAu2In was previously found to be not superconducting above 2 K, and a much earlier report of superconductivity at 3 K was ascribed to elemental indium. In this paper, ScAu2In samples were prepared by the arc-melting method, and its physical properties were revisited by measurement down to 0.4 K. Bulk superconductivity with Tc similar to 1.3 K of ScAu2In has been revealed. The upper critical field mu 0Hc2 of similar to 54.6 mT is well below the Pauli limit, and the gap ratio 2 Delta(0)/kBTc of 2.27 is evidently lower than the value of 3.52, which together indicate that the superconductivity is in the BCS weak-coupling regime. First-principles calculations present the energy bands and density of states (DOS) of ScAu2In, manifesting that it is a multiband metal because different components contribute to the states at the Fermi level (EF). The nearly flat-band topology around the Gamma and L points, and the EF in the vicinity of a van Hove singularity in DOS may boost the superconductivity. Furthermore, non-zero topological indices & Zopf;4 and & Zopf;8 infer that ScAu2In is a candidate of topological superconductor. Our results gain more insights into the superconductivity in Heusler compounds, and provide a platform for probing the interplay between superconductivity and topological states.

A comprehensive spectroscopic map of the electronic, magnetic, and lattice excitations is presented for the bilayer nickelate La_3Ni_2O_7 using Raman scattering at ambient pressure. Upon entering the spin density wave state below 153 K, the A_1g channel exhibits an abrupt electronic spectral gap with a clear isosbestic point. In contrast, the B_1g and B_2g channels are dominated by pronounced two-magnon (2M) excitations, representing an unambiguous signature of incipient Mottness. These 2M signals in both channels constitute direct evidence for two distinct in-plane spin exchange interactions along the Ni-O bonding and its diagonal directions. Calculations based on the spin wave theory further reveal that the 2M mode in the B_2g channel arises from the competition between two bond-diagonal antiferromagnetic interactions mediated by nickel d_x^2-y^2 orbitals. Furthermore, emergent low-energy 2M excitations below 10 meV are found to originate from distinct, weaker spin moments, strongly supporting spin disproportionation. Simultaneously, an anomalous softening of B_1g phonons from 280 down to 4.5 K is uncovered, suggesting the presence of an incipient lattice instability leading to checkerboard-type breathing modulations. Collectively, these findings identify a ground state of the bilayer nickelate characterized by competing bond-diagonal interactions, spin disproportionation, and an incipient lattice instability, establishing key ingredients for understanding the mechanism of nickelate superconductivity.

We report a study of crystal and electronic structures, and superconductivity of the Chevrel-phase (CP) compound NaMo6Se8. Na+ insertion results in a lattice expansion relative to the parent Mo6Se8, and substantially enhances the density of states at the Fermi level within a rigid-band shift picture. Bulk superconductivity with a sharp transition at = 9.7 K is evidenced by electrical transport, magnetic, and thermodynamic measurements. The compound displays an exceptionally large upper critical field & micro; 0 H c2(0) = 33.6 T, almost twice the Pauli paramagnetic limit and placing it among selenide CP superconductors with the highest-H c2 values. Strong spin-orbit scattering offsets the Pauli paramagnetic effect, leading to an enhancement of the effective Pauli-limiting field. Specific-heat data reveal a low-lying Einstein phonon mode associated with Na-cation oscillating, and elucidate the intermediate-coupling two-gap BCS superconductivity. The narrow-band electronic structures, enhanced spin-orbit interactions, and Na-induced low-lying Einstein phonons synergistically promote T c and & micro; 0 H c2. Our work establishes NaMo6Se8 as a compelling high-field superconductor and highlights its promising relevance for high-field superconducting magnets.

Superconductivity was observed in the full-Heusler compound TiPd2Ga below 1.4 K. Polycrystalline samples of TiPd2Ga were prepared by the arc-melting method. TiPd2Ga adopts a centrosymmetric cubic structure with the space group Fm-3m. Electrical-resistivity and magnetic-susceptibility measurements reveal that TiPd2Ga is a type-II superconductor with a large Ginzburg-Landau parameter. The upper critical field & micro;0Hc2 of '2.28 T is slightly lower than the Bardeen-Cooper-Schrieffer Pauli limit (& micro;0HP = 2.58 T) in this three-dimensional superconductor with inversion symmetry, suggesting conventional superconducting states. Thermodynamic and transport data evidence the multigap weak-coupling BCS regime of TiPd2Ga. In addition, we note that a charge density wave like transition lies at '90 K. First-principles calculations indicate that the Pd-4d and Ti-3d orbits dominate the states at the Fermi level (EF), showing that different electronic components induce the multiband characters. The flat band topology and van Hove singularity near EF contribute to the superconducting and charge instabilities in this system. The discovery of the first Ti-containing Heusler superconductor TiPd2Ga may benefit to make sense of the pairing mechanisms of Heusler-phase and other related intermetallic superconductors.

The bilayer nickelate superconductor La3Ni2O7 undergoes a density wave transition near 150 K that has attracted intensive scrutiny, yet its microscopic origin remains elusive. Here we report polarization-resolved electronic Raman scattering measurements on high-quality single crystals of La3Ni2O7. Below 150 K, we observe a pronounced, symmetry-dependent redistribution of spectral weight in B1g and B2g channels, consistent with the formation of spin-density-wave (SDW) gaps. Quantitative analysis reveals momentum-selective SDW gap amplitudes, with intermediate-to-strong coupling near X/Y points of the Brillouin zone and weaker coupling along the diagonal direction, indicating an unconventional SDW driven by anisotropic electronic correlations. Our results establish the electronic character of the SDW in La3Ni2O7, and provide a microscopic foundation for understanding the emergence of high-temperature superconductivity under pressure in nickelates.