Wen-Tao Zhang | Searcharxiv

arXiv2025

Complete suppression of flux instabilities in ramped superconducting magnets with synchronous temperature-modulated Jc

Nonlinear multi-field coupling as an intrinsic property of complex physical systems often leads to abrupt and undesired instabilities. For current-ramped high-field Nb3Sn magnets, frequent flux jumps are observed, which easily causes premature quenches and requires prolonged and resource-intensive magnet training process. In this study, we propose a paradigm-shifting methodology framework that achieves complete suppression of thermomagnetic instabilities through synchronized temperature-modulated critical current density (Jc). Through numerical simulations of flux jumps in multifilamentary Nb3Sn wires at various temperatures, we construct thermomagnetic stability diagram in the Ha-T plane. The simulated results are in good agreement with experiments, confirming that the synchronized temperature ramp-down can fully eliminate flux jumps. We reveal the underlying mechanism of enhancing the thermomagnetic stability arises from that synchronized temperature ramp-down can continuously tune both Jc and its slope. Furthermore, we explore the thermomagnetic instabilities of current-ramped superconducting magnets through large-scale GPU-optimized algorithm. The flux jump and quench diagram in the Ia-T plane are obtained. It indicates that the temperature ramp-down can completely suppress flux jumps without compromising Jc at high magnetic fields. Importantly, this method does not require modifications to the superconducting microstructures or fabrication process, offering a practical and broadly applicable solution. The findings not only provide a robust method for stabilizing various superconducting magnet systems, including high-temperature superconducting magnets wound with second-generated (2G) coated tapes, but also suggest a generalizable strategy for controlling instability in other nonlinear non-equilibrium physical systems.

cond-mat.supr-con↗

arXiv2019

Dirac surface states in intrinsic magnetic topological insulators EuSn2As2 and MnBi2nTe3n+1

In magnetic topological insulators (TIs), the interplay between magnetic order and nontrivial topology can induce fascinating topological quantum phenomena, such as the quantum anomalous Hall effect, chiral Majorana fermions and axion electrodynamics. Recently, a great deal of attention has been focused on the intrinsic magnetic TIs, where disorder effects can be eliminated to a large extent, which is expected to facilitate the emergence of topological quantum phenomena. In despite of intensive efforts, experimental evidence of the topological surface states (SSs) remains elusive. Here, by combining first-principles calculations and angle-resolved photoemission spectroscopy (ARPES) experiments, we have revealed that EuSn2As2 is an antiferromagnetic TI with observation of Dirac SSs consistent with our prediction. We also observe nearly gapless Dirac SSs in antiferromagnetic TIs MnBi2nTe3n+1 (n = 1 and 2), which were absent in previous ARPES results. These results provide clear evidence for nontrivial topology of these intrinsic magnetic TIs. Furthermore, we find that the topological SSs show no observable changes across the magnetic transition within the experimental resolution, indicating that the magnetic order has quite small effect on the topological SSs, which can be attributed to weak hybridization between the localized magnetic moments, from either 4f or 3d orbitals, and the topological electronic states. This provides insights for further research that the correlations between magnetism and topological states need to be strengthened to induce larger gaps in the topological SSs, which will facilitate the realization of topological quantum phenomena at higher temperatures.

cond-mat.mtrl-sci↗