Proximity effect of emergent field from spin ice in an oxide heterostructure

Geometrical frustration endows magnets with degenerate ground states, resulting in exotic spin structures and quantum phenomena. Such magnets, called quantum magnets, can display non-coplanar spin textures and be a viable platform for the topological Hall effect driven by "emergent field." However, most quantum magnets are insulators, making it challenging to electrically detect associated fluctuations and excitations. Here, we probe magnetic transitions in the spin ice insulator Dy2Ti2O7, a prototypical quantum magnet, as emergent magnetotransport phenomena at the heterointerface with the nonmagnetic metal Bi2Rh2O7. Angle-dependent longitudinal resistivity exhibits peaks at the magnetic phase boundaries of spin ice due to domain boundary scattering. In addition, the anomalous Hall resistivity undergoes a sign change with the magnetic transition in Dy2Ti2O7, reflecting the inversion of the emergent field. These findings, on the basis of epitaxial techniques, connect the fundamental research on insulating quantum magnets to their potential electronic applications, possibly leading to transformative innovations in quantum technologies.

Improving the thermal resistance of fluorescent CsPb(Br,I)3 perovskite quantum dots by surface modification with perfluorodecanoic acid

CsPb(Br,I)₃ quantum dots (QDs) show application potential for optoelectronic devices. However, their thermal degradation is a significant problem. In this work, the effects of perfluorodecanoic acid (PFDA) modification on the photoluminescence (PL) and thermal resistance of CsPb(Br,I)₃ QDs were evaluated. The PL intensity of oleic-acid-modified quantum dots (OA-QDs) in toluene decreased drastically upon heating at 100°C. The PL quantum yield of the QDs increased from 69.6% to 77.4% upon modification with PFDA. Furthermore, the PL intensity of the QDs modified with PFDA (PFDA-QDs) increased to 140.6% upon heating, because of the reduction of surface defects upon adsorption of PFDA and its optimized adsorption state. A solid-film PFDA-QDs sample heated at 80°C for 4 h showed temporary PL enhancements for the OA-QDs and PFDA-QDs films to 445% and 557% of their initial values, respectively, upon heating for 0.25 h. This was attributed to the optimized adsorption states of the surface ligands. PFDA-QDs film maintained 354% after 4 h of heating, whereas that of OA-QDs film was 104%. Thus, PFDA modification enhances PL intensity and suppresses PL degradation under heating, which is important for wavelength converters for optoelectronic device applications.

Quantitative Estimate Index for Early-Stage Screening of Compounds Targeting Protein-Protein Interactions

Drug-likeness quantification is useful for screening drug candidates. Quantitative estimates of drug-likeness (QED) are commonly used to assess quantitative drug efficacy but are not suitable for screening compounds targeting protein-protein interactions (PPIs), which have recently gained attention. Therefore, we developed a quantitative estimate index for compounds targeting PPIs (QEPPI), specifically for early-stage screening of PPI-targeting compounds. QEPPI is an extension of the QED method for PPI-targeting drugs that models physicochemical properties based on the information available for drugs/compounds, specifically those reported to act on PPIs. FDA-approved drugs and compounds in iPPI-DB, which comprise PPI inhibitors and stabilizers, were evaluated using QEPPI. The results showed that QEPPI is more suitable than QED for early screening of PPI-targeting compounds. QEPPI was also considered an extended concept of the "Rule-of-Four" (RO4), a PPI inhibitor index. We evaluated the discriminatory performance of QEPPI and RO4 for datasets of PPI-target compounds and FDA-approved drugs using F-score and other indices. The F-scores of RO4 and QEPPI were 0.451 and 0.501, respectively. QEPPI showed better performance and enabled quantification of drug-likeness for early-stage PPI drug discovery. Hence, it can be used as an initial filter to efficiently screen PPI-targeting compounds.

Molecular engineering of Rashba spin-charge converter

In heterostructures with broken inversion symmetry, the electrons' motion is coupled to their spin through interface-driven spin-orbit coupling: the Rashba effect. The Rashba effect enables the interconversion between spin and charge currents, offering a variety of novel spintronic phenomena and functionalities. However, despite the significant progress in Rashba physics, controlling the spin-charge conversion in metallic heterostructures remains a major challenge. We show that molecular self-assembly provides a way to engineer the Rashba spin-charge converters. We demonstrate that magnetoresistance and voltage generation originating from the spin-charge conversion in metallic heterostructures can be manipulated by decorating the surface with self-assembled organic monolayers through the cooperative molecular field effect. We also demonstrate reversible phototuning of the spin-charge conversion through light-driven molecular transformations using a molecule that can photoisomerize between the trans and cis states. These findings, with the almost-infinite chemical tunability of organic monolayers, pave the way toward molecular engineering of spin-orbit devices.

Current-induced magnetization switching using an electrically insulating spin-torque generator

Current-induced magnetization switching through spin-orbit torques is the fundamental building block of spin-orbitronics, which promises high-performance, low-power memory and logic devices. The spin-orbit torques generally arise from spin-orbit coupling of heavy metals. However, even in a heterostructure where a metallic magnet is sandwiched by two different insulators, a nonzero spin-orbit torque is expected because of the broken inversion symmetry; an electrical insulator can be a source of the spin-orbit torques. We demonstrate current-induced magnetization switching using an insulator. We show that oxygen incorporation into the most widely used spintronic material, Pt, turns the heavy metal into an electrically insulating generator of the spin-orbit torques, which enables the electrical switching of perpendicular magnetization in a ferrimagnet sandwiched by insulating oxides. We also show that the spin-orbit torques generated from the Pt oxide can be controlled electrically through voltage-driven oxygen migration. These findings open a route toward energy-efficient, voltage-programmable spin-orbit devices based on insulating metal oxides.

Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions

For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.