Magnetic Transition Research Articles

Influence of local structure and metal-oxygen hybridization on the electrical and magnetic properties of alkaline earth metal (Mg2+, Ca2+, Sr2+) substituted LaFeO3 ceramics

Pristine and alkaline-earth metal-substituted LaFeO3 (La1−xAxFeO3−δ; x = 0 and 0.2; A = Mg2+, Ca2+, and Sr2+) sintered ceramics are prepared from nanoparticles synthesized via a low-temperature citrate sol–gel technique. X-ray diffraction studies confirm the formation of a phase-pure LaFeO3 structure without any secondary phases for all the La1−xAxFeO3−δ compositions. LaFeO3 and La0.8Mg0.2FeO3−δ ceramics show Raman active modes related to La vibration, oxygen octahedral tilting, bending, and stretching. The optical bandgap is estimated to be 2.34 eV for pure LaFeO3 and reduces to 2.23 eV for La0.8Mg0.2FeO3−δ ceramics. On the contrary, La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics show no features in Raman spectra, consistent with the observation of metallic nature and diffuse band edge without any indication of sharp band edge noted. X-ray absorption spectroscopy (XAS) studies on La-L3 and Fe-K-edges confirm the oxidation states of La3+ and Fe3+ in all these ceramics. Local structural distortions and formation of oxygen vacancies in La0.8A0.2FeO3−δ (A = Mg2+, Ca2+, and Sr2+) ceramics are discerned from XAS structure analysis compared to the pristine LaFeO3 ceramics. Magnetic measurements of La1−xAxFeO3−δ reveal weak ferromagnetic nature except for La0.8Mg0.2FeO3−δ, which shows a large magnetization of 4.6 (6.7) emu/g at 300 (5) K. The ferromagnetic behavior of La0.8Mg0.2FeO3−δ ceramics seems to originate from the modification of hybridization between Fe(3d)–O(2p), La(5d)–O(2p), and Fe(4sp)–O(2p) orbitals. An anomalous magnetic transition observed only in zero-field-cooled curves at 88 K in La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics is correlated to the formation of new electronic states containing O 2p character as discerned from pre-peak O-K-edge.

Linking network- and neuron-level correlations by renormalized field theory

It is frequently hypothesized that cortical networks operate close to a critical point. Advantages of criticality include rich dynamics well suited for computation and critical slowing down, which may offer a mechanism for dynamic memory. However, mean-field approximations, while versatile and popular, inherently neglect the fluctuations responsible for such critical dynamics. Thus, a renormalized theory is necessary. We consider the Sompolinsky-Crisanti-Sommers model which displays a well studied chaotic as well as a magnetic transition. Based on the analog of a quantum effective action, we derive self-consistency equations for the first two renormalized Greens functions. Their self-consistent solution reveals a coupling between the population level activity and single neuron heterogeneity. The quantitative theory explains the population autocorrelation function, the single-unit autocorrelation function with its multiple temporal scales, and cross correlations. Published by the American Physical Society 2024

Exploration of near room temperature magnetoelectric coupling in BaFe10Sc[formula omitted]O19:KNbO[formula omitted] composite

The consequential experimental endeavour has been undertaken to investigate and control the strain-mediated coupling of the magnetic and electric properties of the composite systems composed of Sc-doped BaFe12O19 and KNbO3. A distinct non-disperse ferroelectric-like anomaly is observed Tkink∼ 265 K, which concomitantly coincides with the magnetic Tcone transition. The observation of external magnetic field dependence dielectric response shows a noticeable decrease in permittivity values, indicating a negative magnetodielectric response. The maximum intrinsic magnetodielectric response is seen in the vicinity of room temperature with the magnetodielectric ratio of 5.4% @ 1 kHz. The linearity of −Δɛ′(H)% vs. M2 plot is phenomenologically described with the Ginzburg–Landau theory with the magnetoelectric coupling term γP2M2. The magnetoelectric coupling relies on strain to induce crystal deformations (flexomagnetoelectric response) on either the ferroelectric phase through magnetostriction or in the magnetic phase through the converse piezoelectric effect. Strain-induced changes in the magnetic as well as dielectric properties of the composites lead to strong magnetoelectric coupling to throw more light exploring a potential candidate for room-temperature multiferroic materials.

Electron tailoring of thermal and magnetocaloric properties in Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) metallic glasses

Transition metal (TM) elements play a key role in determining properties of magnetocaloric materials. However, the effect of TM elements on the thermodynamic behavior and magnetocaloric effect (MCE) of metallic glasses (MGs) remains elusive. In this work, ternary Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) MGs without the complexities induced by high-entropy effects were designed. It is found that both the glass transition temperature (Tg) and the initial crystallization temperature (Tx) significantly increase with decreasing 3d electron number. It leads to the low values of Trg, γ, and γm for Tb55Fe17.5Al27.5, which is consistent with its poor glass forming ability (GFA) as evidenced by the obvious lattice fringes and structural order. Despite the mediocre value of magnetic entropy change (|ΔSMpk|) for Tb55Fe17.5Al27.5, its broader magnetic transition temperature of 110.4 K associated with ∼26% evident structural order yields the maximum relative cooling power (RCP) of 546.04 J kg−1 among three MGs. Moreover, a novel weighted method for evaluating 3d electron number by consideration of the concentration and species of TM elements was adopted to reveal an inverse correlation between the 3d electron number and Tg/Tx, as well as curie temperature (Tc), |ΔSMpk|, and RCP. It is found that with the decrease of the weighted 3d electron number of TM elements, the thermal stability of rare-earth-base MGs is effectively enhanced ascribed to the strong f - d orbital hybridization effect, along with the enhanced 3d - 3d exchange interaction that induces a high Tc. This work would help us more deeply understand the role of TM elements from the perspective of electronic structure, which is crucial for designing the novel MGs with a tunable MCE and GFA applied in various cryogenic refrigeration fields.

Quantum geometry quadrupole-induced third-order nonlinear transport in antiferromagnetic topological insulator MnBi2Te4

The study of quantum geometry effects in materials has been one of the most important research directions in recent decades. The quantum geometry of a material is characterized by the quantum geometric tensor of the Bloch states. The imaginary part of the quantum geometry tensor gives rise to the Berry curvature while the real part gives rise to the quantum metric. While Berry curvature has been well studied in the past decades, the experimental investigation on the quantum metric effects is only at its infancy stage. In this work, we measure the nonlinear transport of bulk MnBi2Te4, which is a topological anti-ferromagnet. We found that the second order nonlinear responses are negligible as required by inversion symmetry, the third-order nonlinear responses are finite. The measured third-harmonic longitudinal (Vxx3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{{xx}}^{3\\omega }$$\\end{document}) and transverse (Vxy3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{{xy}}^{3\\omega }$$\\end{document}) voltages with frequency 3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document}, driven by an a.c. current with frequency ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document}, show an intimate connection with magnetic transitions of MnBi2Te4 flakes. Their magnitudes change abruptly as MnBi2Te4 flakes go through magnetic transitions from an antiferromagnetic state to a canted antiferromagnetic state and to a ferromagnetic state. In addition, the measured Vxx3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{{xx}}^{3\\omega }$$\\end{document} is an even function of the applied magnetic field B while Vxy3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{{xy}}^{3\\omega }$$\\end{document} is odd in B. Amazingly, the field dependence of the third-order responses as a function of the magnetic field suggests that Vxx3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{{xx}}^{3\\omega }$$\\end{document} is induced by the quantum metric quadrupole and Vxy3ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${V}_{{xy}}^{3\\omega }$$\\end{document} is induced by the Berry curvature quadrupole. Therefore, the quadrupoles of both the real and the imaginary part of the quantum geometry tensor of bulk MnBi2Te4 are revealed through the third order nonlinear transport measurements. This work greatly advanced our understanding on the connections between the higher order moments of quantum geometry and nonlinear transport.

Doping position estimation for FeRh-based alloys

FeRh-based alloys have attracted significant attention due to their magnetic phase transition and significant magnetocaloric effects. These properties position them as promising candidates for fundamental research and practical applications, including magnetic cooling and targeted drug delivery. The study of FeRh alloys, particularly those where Rhodium or Iron atoms are substituted with other transition metals, is crucial as certain substitutions preserve the alloy’s magnetocaloric properties. However, even within a specific structural type and without considering competing phases, determining which atom (Fe or Rh) is replaced upon introducing a third element remains unclear. This paper addresses this ambiguity through ab initio calculations. We propose an approach to predict whether a dopant will replace Fe or Rh, offering insights into the electronic and structural factors influencing the substitution. Additionally, we present a dataset of ab initio calculations on doped FeRh alloys, which will support future data-driven modeling efforts. Our findings not only advance the understanding of FeRh-based alloys but also contribute to the design of novel materials for experimental and industrial applications.

Multiple magnetic orders discovered in the superconducting state of EuFe2(As1−xPx)2

Abstract The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe2As2-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe2As2-based crystal, which were deemed to originate from the itinerant Fe moments ( 190 K) and the localized Eu2+ moments ( 19 K), respectively. Here, we systematically studied the heat capacity for the EuFe2(As1−xPx)2 crystals with x = 0.21 (optimally doped) and x = 0.29 (overdoped). We have found two new magnetic orders in the superconducting state (ranging from 0.4 to 1.2 K) in the optimally doped crystal. As more P was introduced into the As site, one of the magnetic orders becomes absent in the overdoped crystal. Additionally, we observed strong field and orientation dependence in heat capacity. The present findings in EuFe2(As1−xPx)2 have detected the new low-temperature magnetic orders, which may originate from the localized Eu2+ spins order or the spin reorientation.

In-situ momentum dispersion in a single crystal of MoS2

In this letter, we investigate the momentum dispersion in a MoS2 flake as a function of the thickness in a single crystal with several height steps. The outcomes of our study rely on the utilization of near-field microscopy and an excitation field in the strong-coupling regime. The observed propagating modes have characteristics that are consistent with transverse magnetic (TM) modes, which can be attributed to the investigated thicknesses. Numerical simulations support our experimental findings and correspond with previously reported studies.

Design and experimental validation of a compact dual-band metamaterial perfect absorber for electromagnetic energy harvesting applications

This article introduces, characterizes, and experimentally validates an innovative design for a compact-sized metamaterial (MM) perfect absorber (PA) for electromagnetic (EM) energy harvesting (EH) applications. The absorber design, comprised of three octagonal ring resonators made of annealed copper, incorporates split gaps at 45-degree inclinations within the uppermost and middle resonators. A split strip line connects the inner octagonal ring resonators, while the split gaps of the outermost and inner rings are filled with a 50 Ω resistive load. This structure is made on a Rogers RT5880 substrate, and the back side of the proposed design is entirely coated with annealed copper. The proposed absorber achieves precise impedance matching with free space, facilitating efficient absorption and redirecting EM power toward the resistive loads. The absorber demonstrates absorption peaks of 99.98 % at 2.4 GHz and 99.99 % at 4.9 GHz. In addition, the efficiency of absorption is assessed for different incident (θ) and polarization angles (ϕ) in both the Transverse Electric (TE) and Transverse Magnetic (TM) modes. Simulated harvesting efficiencies of 95.33 % at 2.4 GHz and 95.99 % at 4.9 GHz are recorded. An experimental validation is performed using a 3 × 3 array that measures 30 × 30 mm. The tests are carried out in an anechoic chamber. The measured harvesting efficiencies strongly correlate with the simulated results, indicating the reliability of the proposed design. This absorber's efficiency and compact size make it an excellent option for EH systems in wireless sensor networks (WSNs).

Construction of rGO-MXene@FeNi/epoxy composites with regular honeycomb structures for high-efficiency electromagnetic interference shielding

With the rapid development of 5G communication technology and wearable electronic devices, the demand for low-reflection electromagnetic interference (EMI) shielding materials is becoming increasingly urgent. In this work, reduced graphene oxide-MXene (rGMH) @FeNi/epoxy EMI shielding composites with a regular honeycomb structure were successfully prepared by the combination of surface functionalization modification, sacrificial template, and freeze-drying. The effects of magnetic FeNi alloy particle loading mode and loading amount on the EMI shielding performance of composites were investigated. The results show that rGMH@FeNi/epoxy EMI shielding composites have the highest EMI shielding effectiveness (EMI SE) and the lowest reflection shielding effectiveness when magnetic FeNi alloy particles are loaded only on the graphene skeleton. In this composite, the EMI SE value of the composite is 61 dB when the rGMH@FeNi mass fraction is 5.4 wt% (f-FeNi mass fraction is 0.9 wt%), which is 4.7 times that of the blended rGO/MXene/FeNi/ epoxy resin composite (13 dB) with the same mass fraction. At the same time, the rGMH@FeNi/epoxy composite has excellent thermal stability (heat-resistance index of 190.3 °C) and mechanical properties (energy storage modulus of 8606.7 MPa). These polymer-based EMI shielding composites with excellent EMI shielding properties and low reflection effectiveness have great potential in the protection of high-power, portable and wearable electronic devices against electromagnetic pollution.

Disentangling different interfacial effects of reduced thin layer magnetizations

Abstract Thin buried magnetic layers ranging from thicknesses of a few atomic monolayers to several nanometers are omnipresent in the fields of magnetism and spintronics. For the functionality and fine tuning of devices build with such layers, exact knowledge of the depth dependent magnetic properties is essential. Especially the interfacial magnetic properties are important. Hence, understanding how magnetism is affected by structural variations, such as thickness or interface roughness, is mandatory. In this study, we use x-ray resonant magnetic reflectometry and magnetometry to study the high-resolution depth dependent magnetization profiles of thin magnetic transition metal layers sandwiched between an oxide and chromium layer. Compared to bulk materials, the room temperature saturation magnetization of these layers is reduced by up to 67%. These reductions are extremely sensitive to small structural variations. From the magnetic depth profiles, we disentangle different effects contributing to the magnetization reduction and the exact magnetic properties of the interface.

Large magnetocaloric effect of RCoSn (R=Dy, Ho, Er and Tm) compounds

Materials with large magnetocaloric effect (MCE) at low temperatures under low field changes play an important role in the application of cryogenic magnetic refrigeration and attract extensive research interests of researchers. In this work, four ternary rare-earth-based RCoSn (R=Dy, Ho, Er and Tm) compounds were successfully synthesized and the crystal structure, magnetic properties, magnetic phase transition, and magnetocaloric effects were systematically studied. RCoSn (R=Dy, Ho, Er and Tm) compounds all crystallize in orthorhombic TiNiSi-type structure and undergo an antiferromagnetic (AFM) to paramagnetic (PM) transition with Neél temperature of 11.0, 7.9, 4.9 and 3.0 K, respectively. Large cryogenic MCE of RCoSn (R=Dy, Ho, Er and Tm) with the maximum magnetic entropy change (−ΔSMmax) of 10.6, 13.7, 17.1, 13.4 J/kg K for field change of 0–5 T was obtained. Furthermore, the value of −ΔSMmax for ErCoSn and TmCoSn is as high as 11.3 and 10.1 J/kg K for field change of 0–2 T, which is very competitive among low temperature magnetocaloric materials. The characteristic of second order magnetic phase transition indicates RCoSn (R=Dy, Ho, Er and Tm) compounds have good magnetic/thermal reversibility. These results show that RCoSn compounds, especially ErCoSn and TmCoSn, exhibit promising MCE and have great application potential in cryogenic magnetic refrigeration.

Prognostic value of novel cardiovascular magnetic resonance transit times beyond the pulmonary circulation in patients with ventricular dysfunction.

To evaluate the prognostic value of transit time (TT) assessment in the systemic circulation and organ perfusion in patients with ventricular dysfunction (VD). The primary endpoint was defined as death, heart failure admission, or ventricular arrhythmias, and the secondary endpoint was worsening renal function. A retrospective study on 139 patients who underwent cardiac magnetic resonance for VD evaluation and 50 controls. TT was measured as peak-to-peak time in signal intensity over time curves obtained at different stages of circulation (right cavities, left cavities, aorta, and peripheral organs) from first-pass perfusion images. Outcomes were monitored over a median follow-up of 15 months. A total of 139 patients were included (84% male, age 63 [57-70] years). Patients exhibited significantly prolonged TT compared to controls, with in-patients showing longer times than outpatients. Among the 29 patients reaching the primary endpoint, both PTT and STT were significantly prolonged (PTT: 9.75 s vs 13.4 s, p < 0.01; STT: 4.77 s vs 7.00 s, p < 0.01). Concurrent prolongation of PTT (> 10 s) and STT (> 5 s) was associated with a higher event probability (42.3%), compared to isolated abnormalities (6.3% for PTT, 6.7% for STT). Multivariate analysis revealed that combined PTT and STT alteration independently predicted the combined endpoint (HR IC 95%: 8.685 (2.415-31.236), p = 0.001). Prolonged RPT was independently associated with renal function deterioration (OR IC 95%: 1.129 (1.015-1.256), p = 0.024). Evaluation of TT beyond pulmonary circulation provides prognostic insights into VD. Simultaneous assessment of PTT and STT enhances specificity compared to isolated PTT evaluation, predicting combined adverse events. RPT is independently associated with renal impairment. For the first time, it is described that transit time can be evaluated in systemic circulation and in peripheral organs and that this assessment can be easily made from conventional CMR perfusion images and holds significant prognostic value. Pulmonary transit time is a valuable hemodynamic parameter; systemic transit time may also be valuable. Transit time can be measured in the systemic circulation, and is longer in patients with ventricular dysfunction. Systemic transit time assessed by magnetic resonance imaging identifies patients with ventricular dysfunction who will experience events during follow-up.

Anisotropy-driven magnetic phase transitions in SU(4)-symmetric Fermi gas in three-dimensional optical lattices

Abstract We study SU(4)-symmetric ultracold fermionic mixture in the cubic optical lattice with the variable tunneling amplitude along one particular crystallographic axis in the crossover region from the two- to three-dimensional spatial geometry. To theoretically analyze emerging magnetic phases and physical observables, we describe the system in the framework of the Fermi-Hubbard model and apply dynamical mean-field theory. We show that in two limiting cases of anisotropy there are two phases with different antiferromagnetic orderings in the zero temperature limit and determine a region of their coexistence. We also study the stability regions of different magnetically-ordered states and density profiles of the gas in the harmonic optical trap.&amp;#xD;

Anisotropy of the magnetocaloric effect in MnAs single crystal

The magnetic and magnetocaloric properties of a MnAs single crystal have been studied along different crystallographic directions in the temperature range of the first-order magnetic phase transition. The constants of magnetocrystalline anisotropy, K1 and K2, were determined below the transition temperature by the Sucksmith-Thompson method. It was found that the energy of magnetocrystalline anisotropy decreases with increasing temperature. The results highlighted the impact of shape anisotropy and the magnetic prehistory of the sample on the maximum value of −ΔSm. The anisotropy of the −ΔSm value was observed for different crystallographic directions; the −ΔSm value reaches its maximum of 35 J∙kg−1∙K−1 in the [001] direction, while 29 J∙kg−1∙K−1 in the [110] direction. The probability of overestimating the ΔSm(T) values when using Maxwell’s equation instead of the Clausius-Clapeyron formula is shown.

Tunable terahertz meta-resonator with switchable single- and dual-resonance characteristic

A tunable terahertz meta-resonator (TTM) is proposed to be capable of switching single- and dual-resonance characteristics in this article. The presented TTM device consists of two symmetrical E-shaped electric split-ring resonators (eSRRs) on the silicon (Si) substrate. Through the change of the gap between two eSRRs, it allows the resonances to be tuned about 78 GHz, spanning from 0.780 THz to 0.702 THz in transverse magnetic (TM) mode. When one eSRR is anchored on the Si substrate and the other suspended eSRR is heightened along the z-axis direction, the TTM device exhibits resonance-insensitive behavior in transverse electric (TE) mode, along with a convertible feature that enables it to transition between single-resonance and dual-resonance responses in TM mode. Besides, the practicality of TTM device is further enhanced by its capability to operate effectively in ambient surroundings with varying refractive indexes. In TE and TM modes, the high linearity relationship between resonances and refractive indexes is achieved with correlation coefficients both exceeding 0.99. The TTM device provides potential possibilities in tunable filters, switchable logic gates, environmental sensors, and other dynamically controllable THz-wave optoelectronics devices.

Achieve outstanding refrigeration performance near ambient temperature in a Fe88Pr8B2Ce2 amorphous ribbon

A novel Fe88Pr8B2Ce2 amorphous alloy (AA) with outstanding magnetocaloric effect near 295 K was vitrified into ribbon. The Fe88Pr8B2Ce2 ribbon exhibits a typical 2nd-order magnetic transition with a peak value of magnetic entropy change (−ΔSmpeak) of ∼ 4.34 J·kg−1·K−1 near its Curie temperature (Tc, ∼ 295 K) under 5 T, which is the highest among the AAs reported in the literature with Tc = 295±10 K. The temperature averaged entropy change (TEC) for the household air conditioner (TECAC) and refrigerator (TECR) were defined to evaluate the refrigeration performance of the magnetic refrigerants in these cooling facilities. TECAC and TECR for the Fe88Pr8B2Ce2 AA reach to 4.21 J·kg−1·K−1 and 3.93 J·kg−1·K−1, both of which are also much larger than those of other AAs with Tc near 295 K and indicate the better application perspective of the Fe88Pr8B2Ce2 AA as the magnetic refrigerants working in the residential magnetic air conditionings and refrigerators.

Superconductivity under pressure in a chromium-based kagome metal.

Superconductivity in a highly correlated kagome system has been theoretically proposed for years (refs. 1-5), yet the experimental realization is hard to achieve6,7. The recently discovered vanadium-based kagome materials8, which exhibit both superconductivity9-11 and charge-density-wave orders12-14, are nonmagnetic8,9 and weakly correlated15,16. Thus these materials are unlikely to host the exotic superconductivity theoretically proposed. Here we report the discovery of a chromium-based kagome metal, CsCr3Sb5, which is contrastingly featured with strong electron correlations, frustrated magnetism and characteristic flat bands close to the Fermi level. Under ambient pressure, this kagome metal undergoes a concurrent structural and magnetic phase transition at 55 K, with a stripe-like 4a0 structural modulation. At high pressure, the phase transition evolves into two transitions, possibly associated with charge-density-wave and antiferromagnetic spin-density-wave orderings. These density-wave-like orders are gradually suppressed with pressure and, remarkably, a superconducting dome emerges at 3.65-8.0 GPa. The maximum of the superconducting transition temperature, Tcmax = 6.4 K, appears when the density-wave-like orders are completely suppressed at 4.2 GPa, and the normal state exhibits a non-Fermi-liquid behaviour, reminiscent of unconventional superconductivity and quantum criticality in iron-based superconductors17,18. Our work offers an unprecedented platform for investigating superconductivity in correlated kagome systems.

Significantly Promoting the Thermal Conductivity and Machinability of Negative Thermal Expansion Alloy via In Situ Precipitation of Copper Networks.

Rapid advancements in electronic devices yield an urgent demand for high-performance electronic packaging materials with high thermal conductivity, low thermal expansion, and great mechanical properties. However, it is a great challenge for current design philosophies to fulfill all the requirements simultaneously. Here, an effective strategy is proposed for significantly promoting the thermal conductivity and machinability of negative thermal expansion alloy (Zr,Nb)Fe2 through eutectic precipitation of copper networks. The eutectic dual-phase alloy exhibits an isotropic chips-matched thermal expansion coefficient and a thermal conductivity enhancement exceeding 200% compared with (Zr,Nb)Fe2, along with an ultimate compressive strength of 550MPa. The addition of copper reorganizes the composition of (Zr,Nb)Fe2, which smooths the magnetic transition and shifts it toward higher temperature, resulting in linear low thermal expansion in a wide temperature range. The highly fine eutectic copper lamellae construct high thermal conductivity networks within (Zr,Nb)Fe2, serving as highways for heat transfer electrons and phonons. The in situ forming of eutectic copper lamellae also facilitates the mechanical properties by enhancing interfacial bonding and bearing additional stress after yielding of (Zr,Nb)Fe2. This work provides a novel strategy for promoting thermal conductivity and mechanical properties of negative thermal expansion alloys via eutectic precipitation of copper networks.

Topological polarization beam splitter based on directional coupling between asymmetric valley photonic crystal waveguides.

Compared with symmetric directional couplers (DCs), asymmetric DCs constructed by two or over two different parallel waveguides offer a more flexible structure and allow for easier expansion of mode channels. In this Letter, we propose a kind of asymmetric topological DC based on two different valley photonic crystal waveguides (VPCWs). According to the coupled-mode theory, phase matching induces the complete coupling for the guide modes of two different VPCWs, whereas significant phase mismatching indicates no coupling occurs. Furthermore, the asymmetric topological DCs exhibit backscattering immunity and anti-disturbance robustness owing to the topological edge states (TESs), which greatly improve the performance of asymmetric DCs. We further design a new, to the best of our knowledge, kind of topological polarization beam splitter (TPBS) at the communication wavelength of 1550 nm by ensuring that the transverse electric mode satisfies the phase matching condition, while the transverse magnetic mode is phase-mismatched. The simulated results demonstrate that the proposed TPBS exhibits highly effective polarization separation and is robust against defects. This design holds significant potential for applications in optical communication systems.