Journal of Superconductivity and Novel Magnetism最新文献

The recently emerged field of Terahertz spectroscopy provides an important tool for studying the relaxation and various excitations at a previously inaccessible energy scale which is especially important in superconductors. Sufficiently strong fields allow to examine nonlinear effects such as higher harmonic generation. In this work, we study the photoinduced current resulting from an exposure of a clean and uniform conducting material to sufficiently strong radiation. The phenomenon of photoinduced current can be observed in either bulk non-centrosymmetric materials or in certain sample geometries where a designated direction is introduced, for example, thin films. We explore the implications of the approximate electron momentum conservation in clean metals. We find a universal relation which expresses the essentially nonlinear zero frequency photoinduced current through the first-order conductivity in non-isotropic geometries where it is facilitated by the excitation of plasma modes. Our results are relevant for various clean materials and can be directly checked in experiments on photocurrent measurements.

For an epitaxial film of an electron-doped superconductor ({text{Nd}}_{2-x}{text{Ce}}_{x }{text{CuO}}_{4}) (x = 0.145), in a mixed state, a well-defined step structure is observed on the dependence of the c-axis resistance on the magnetic field parallel to CuO₂ layers. It is shown that in the region of the free flow of Josephson vortices, an exponential dependence of monotonous ({R}_{c}(B)) component in the flux-flow mode is observed. The "quantized" steps of equal height in the actual range of magnetic fields were registered with a period of (Delta Bsim {Phi }_{0}/left({lambda }_{ab}{lambda }_{c}right)) where the magnetic penetration depths in the ab-plane (({lambda }_{ab})) and along the c-axis (({lambda }_{c})) determine the sizes of the Josephson vortices in anisotropic layered superconductor. We associate the periodic steps of magnetoresistance with the resonant response of the system under study to the magnetic field-induced change in the number of Josephson vortices, each of which contains a magnetic flux quantum.

The evolution with interaction of the electronic structure of the triangular Hubbard model, which is believed to be the parent model for describing the electronic structure of twisted bilayer dichalcogenides, is studied within the cluster perturbation theory using 13-site clusters. Local and non-local correlations are taken into account within a cluster, while the intercluster hopping is considered using perturbation theory. We obtain the evolution of the electronic structure from metal to insulator through the pseudogap state with increasing interaction. We show that this pseudogap state is characterized by the arc–like Fermi surface with maximum spectral weight located in the (Gamma -K) directions. The energy distribution curves at the Fermi level are not characterized by a strong spectral function peak. Such momentum-dependent behavior of pseudogap suppression of spectral function is not typical for the most familiar pseudogap in doped cuprates in the presence of strong antiferromagnetic correlations and can lead to momentum-uniform pseudogap.

To analyze the effect of sodium doping on iron-selenide 122 superconductors family we have grown crystals of (Na, K, Rb)Fe₂Se₂. Using resistive and magnetic probes it was confirmed that Na_0.27K_0.27Rb_0.27Fe₂Se₂ shows high quality and homogeneity of the superconducting properties below T_c ≈ 32 K. The morphology and composition were studied for this sample as seen via electron microscopy and showed the presence of a new sodium-rich phase.

Ce_1 − xFe_xO₂ (x ≤ 0.05) nanoparticles were synthesized via chemical co-precipitation and characterized for structural, thermal, optical, and magnetic properties. XRD confirmed a single-phase cubic fluorite structure, while EDX verified near-stoichiometric composition. FE-SEM and TEM showed uniformly distributed nanocrystals (~ 11 nm). TGA with Coats-Redfern analysis indicated enhanced oxygen-ion mobility and defect-assisted thermal behavior for Ce_0.95Fe_0.05O₂ (Eₐ = 7.91 kJ) compared to CeO₂ (Eₐ = 10.38 kJ). Optical studies revealed a band gap reduction (2.82 → 2.58 eV) and improved visible-light absorption with Fe doping. The magnetic parameters (M_s ~ 0.003–0.004 emu/g, H_c ~ 250–300 Oe) confirm the presence of weak, defect-mediated ferromagnetism originating from oxygen-vacancy-induced F-center exchange. Compared with earlier sol-gel and hydrothermal Fe–CeO₂ reports, this work uniquely correlates co-precipitation–derived oxygen vacancy density with thermodynamic and magnetic behavior. These results highlight the role of defect engineering in tuning the multifunctional properties of Fe-doped CeO₂ for spintronic applications.

We study the Fermi surface topology of a two-dimensional electron gas (2DEG) proximitized by d-wave superconductors in a linear superconductor–normal–superconductor (SNS) Josephson junction with a (pi) phase difference. Owing to nodal quasiparticles and the anisotropic gap, the d-wave case differs qualitatively from the isotropic s-wave case: the nonlocal conductance is no longer directly tied to the number of critical points on the Fermi surface. Instead, we show that the rectified conductance remains quantized at low bias and faithfully encodes the Fermi surface topology via the Euler number (chi _F). This quantized response persists even for complex or multi-pocket Fermi surfaces, establishing rectified conductance as a robust and experimentally accessible probe of Fermi surface topology in gapless superconductors.

This work addresses the two major bottlenecks hindering the application of Bi2212 high-temperature superconducting round wires: the high technical barrier of the required heat treatment and its prohibitive cost. Our team has broken the heat-treatment bottleneck by independently developing a series of high-pressure heat treatment (HPHT) systems, which are capable of processing coils with bore sizes up to 20 cm and have provided sintering services to multiple research institutions. Concurrently, we have established a full-chain batch fabrication process from precursor powder to coil sintering. We have achieved batch production of Bi2212 wires with single lengths exceeding 1000 m and an annual capacity of 200 km. These wires exhibit a critical current (I_c) ≥ 496 A at 4.2 K and 12 T, and a hysteresis loss as low as 589 mJ/cm³, approaching the ITER standard. For cabling compatibility, strands extracted from cables retained 87.9% to 95.7% of their critical current after bending and straightening. The production scale-up has drastically reduced costs, and these wires have been successfully validated in small coils, Bi2212 CICC conductors, and D-shaped coils, thereby effectively mitigating the two initial challenges and laying a solid foundation for the large-scale application of Bi2212. ✉ Qingbin Hao. HaoQB@c-nin.com. Shengnan Zhang. snzhang@c-nin.com. 1. Superconducting Materials Research Center, Northwest Institute for Non-ferrous Metal Research, Xi’an 710,016, People’s Republic of China. 2. Western Superconducting Technologies Co., Ltd, Xi’an 710,018, People’s Republic of China.

This paper reports a first-principles study on structural, electronic, and magnetic properties of the ZnI₂ monolayers doped with 3d transition-metal (TM) atoms (from Sc to Cu). We investigate the effect of TM substitution on the electronic band structure, density of state, spin polarization, magnetic moment, and charge distribution using spin-polarized density functional theory within the generalized gradient approximation (GGA). The pristine ZnI₂ monolayer is confirmed to be a non-magnetic indirect semiconductor with a band gap of 2.002 eV. We find that the TM doping of ZnI2 can result in various electronic properties: Sc-doping yields a nearly semimetallic gap (0.006 eV), Ti- and Co-doping produce spin-polarized semiconductors with gaps of 0.210 eV and 0.296 eV, respectively; Cr-, Fe-, and Cu-doped systems exhibit half-metallic behavior with band gaps of 0.0006 eV, 0.0014 eV, and 0.0022 eV, respectively. V-, Mn-, and Ni-doped systems lead to bipolar magnetic semiconductors with total gaps of 0.8584 eV, 1.4865 eV, and 0.8407 eV, respectively. The computed magnetic moments increase from 0.89(::{mu:}_{B}) (Sc) to 5.00 (:{mu:}_{B}) (Mn) and then decrease towards 1.00 (:{mu:}_{B}) (Cu) as the 3d orbitals are filled. Overall, these results show a clear and progressive evolution in the system’s behavior from semimetallic to spin-polarized semiconducting, bipolar magnetic semiconducting, and finally half-metallic states, reflecting how the 3d orbital filling systematically modifies the electronic and magnetic characteristics of the ZnI₂ lattice. The spin density indicates the localized or delocalized magnetic behavior of the dopant, and the charge analysis confirms the partial electron transfer, which is related to the occupation of the d-orbital. Such tunable changes in the magnetic and electronic states suggest that 3d transition-metal doping offers a practical pathway to engineer ZnI₂ monolayers for spintronic and magneto-electronic applications.

The ferromagnetic resonance (FMR) behavior of patterned nickel magnonic crystals is shown to be strongly governed by the geometry and thickness of the individual nanostructures. Arrays of square, triangular, and circular nanopillars fabricated by electron beam lithography exhibit a clear inversion in the resonance field order between in-plane (S2 > S1 > S3) and out-of-plane (S2 < S3 < S1) configurations. This inversion arises from the interplay between shape-induced anisotropy and thickness-related dimensional effects. Micromagnetic simulations corroborate the experimental findings, revealing how the dipolar field distribution and edge curvature modulate local magnetization dynamics. The results establish geometry as an efficient tuning parameter for FMR responses in magnonic systems, opening new pathways for the design of spintronic components and high-frequency magnetic devices based on controlled anisotropy engineering.

The structural, magnetic, and dielectric properties of Cr-substituted samarium iron garnet ((S{m}_{3}:F{e}_{5-x}:C{r}_{x}:{O}_{12},:x:=:0.0-0.5)) were systematically investigated to understand the impact of Cr incorporation on the garnet framework. X-ray diffraction analysis confirmed single-phase cubic garnet formation, accompanied by a gradual reduction in lattice parameter and grain size with increasing Cr content. Magnetic measurements revealed two characteristic spin-reorientation transitions in the parent compound, both of which became progressively suppressed upon Cr substitution due to the weakening of (Feleft(aright)-O-Feleft(dright)) superexchange interactions. A consistent decrease in magnetization was observed as magnetic (Fe^{3+}) ions were replaced by lower-moment (Cr^{3+}) ions. Impedance spectroscopy demonstrated clear dielectric relaxation behavior, with relaxation peaks shifting toward higher frequencies for Cr-doped samples that indicates reduced relaxation time and enhanced charge transport. Overall, Cr substitution effectively tunes the magnetic ordering, microstructure, and dielectric response of SmIG, highlighting its potential for multifunctional magneto-dielectric and high-frequency device applications.