Quantum matter in high magnetic fields

Abstract:

ABSTRACT Lead‐free dielectric capacitors require high‐recoverable energy density and thermal stability under low operating fields to prevent premature breakdown. Here, we demonstrate a design strategy for high‐performance lead‐free dielectrics based on two key principles: selecting a highly polarizable ferroelectric matrix and engineering local polar frustration to suppress long‐range order and stabilize an ergodic relaxer state. Using the (0.94Na 0.5 Bi 0.5 TiO 3 ‐0.06BaTiO 3 )–x(0.85NaNbO 3 ‐0.15CaTiO 3 ) (NBT‐BT‐NN‐CT) as an exemplar in this work, structural analyses reveal that NN‐CT incorporation induces a frustrated polar structure characterized by the nanoscale coexistence of rhombohedral, tetragonal, and cubic‐polymorphs. Density functional theory confirms that energetic degeneracy physically prevents the formation of stable macro‐domains. The optimal composition yields wide temperature stability (±15% permittivity up to 370°C), far exceeding the X7R industrial standard, delivering a recoverable energy density of >5 J cm −3 under low field (250 kV cm −1 ) achieving an ultrahigh normalized energy density (W a ) of >0.020 mC cm −2 , 60% improvement over conventional NBT‐based counterparts in the literature (e.g., 0.012–0.015 mC cm −2 ). Furthermore, in situ synchrotron X‐ray diffraction (<160 kV cm −1 ) provides strong crystallographic evidence of this dynamic structural stability, confirming the absence of irreversible field‐induced phase transitions. These results establish polar frustration engineering as a transferable design principle for resilient, high‐performance lead‐free dielectrics.

Abstract:

Chemical recycling of polystyrene (PS), one of the most common and abundant plastic materials manufactured around the globe, is vital for reducing plastic waste, mitigating environmental impacts, and providing economically viable solutions that support a sustainable future. The ongoing efforts in PS degradation promise to enhance this process as a key technology in the transition toward a circular society. However, the highly durable nature of PS, which is composed of only hydrocarbon backbones, hampers the implementation of chemical recycling. Multiple radical mechanisms involved in the pyrolysis of PS cause a broad product distribution, which considerably decreases the recovery of the desired monomer. Here, we show a methodology to realize the highly efficient thermal depolymerization of PS mediated by nanoporous metal-organic frameworks (MOFs). Nanoconfinement of PS into a MOF enables a consolidation of complex degradation pathways in the nanochannels, restraining the formation of undesirable heavy oil components made of styrene oligomers and more selectively generating styrene monomers. By leveraging nanoconfinement effects on polymer degradation, this novel protocol demonstrates remarkable depolymerization behaviors with high scalability and practicality, just by treating MOFs and PS together at elevated temperatures, with the potential to become a game-changing technology in the chemical recycling of plastic waste.

Abstract:

Electronic scattering is a powerful tool to identify underlying changes in electronic behavior and incipient electronic and magnetic orders. The nematic and magnetic phases are strongly intertwined under applied pressure in FeSe, however, the additional isoelectronic substitution of sulfur offers an elegant way to separate them. Here we report the detailed evolution of the electronic and superconducting behavior of ${\mathrm{FeSe}}_{0.96}{\mathrm{S}}_{0.04}$ under applied pressure via longitudinal magnetoresistance studies up to 15 T. At intermediate pressures, inside the nematic phase, the resistivity displays an upturn in zero magnetic field, which is significantly enhanced in the magnetic field, suggesting the stabilization of a spin-density wave phase, which competes with superconductivity. At higher pressures, beyond the nematic phase boundaries, the resistivity no longer displays any clear anomalies in the zero magnetic field, but an external magnetic field induces significant upturns in resistivity reflecting a field-induced order, where superconductivity and magnetic anomalies are enhanced in tandem. This study highlights the essential role of high magnetic fields in stabilizing different electronic phases and revealing a complex interplay between magnetism and superconductivity tuned by applied pressure in ${\mathrm{FeSe}}_{1-x}{\mathrm{S}}_x$ .