Even-Odd Layer-Dependent Exchange Bias Effect in MnBi2Te4 Chern Insulator Devices.

Magnetic topological materials with coexisting magnetism and nontrivial band structures exhibit many novel quantum phenomena, including the quantum anomalous Hall effect, the axion insulator state, and the Weyl semimetal phase. As a stoichiometric layered antiferromagnetic topological insulator, thin films of MnBi2Te4 show fascinating even-odd layer-dependent physics. In this work, we fabricate a series of thin-flake MnBi2Te4 devices using stencil masks and observe the Chern insulator state at high magnetic fields. Upon magnetic field training, a large exchange bias effect is observed in odd but not in even septuple layer (SL) devices. Through theoretical calculations, we attribute the even-odd layer-dependent exchange bias effect to the contrasting surface and bulk magnetic properties of MnBi2Te4 devices. Our findings reveal the microscopic magnetic configuration of MnBi2Te4 thin flakes and highlight the challenges in replicating the zero magnetic field quantum anomalous Hall effect in odd SL MnBi2Te4 devices.

Environmental Doping-Induced Degradation of the Quantum Anomalous Hall Insulators.

The quantum anomalous Hall (QAH) insulator carries dissipation-free chiral edge current and thus provides a unique opportunity to develop energy-efficient transformative information technology. Despite promising advances, the QAH insulator has thus far eluded any practical applications. In addition to its low working temperature, the QAH state in magnetically doped topological insulators usually deteriorates with time in ambient conditions. In this work, we store three QAH devices with similar initial properties in different environments. The QAH device without a protection layer in air shows clear degradation and becomes hole-doped. The QAH device kept in an argon glovebox without a protection layer shows no measurable degradation after 560 h, and the device protected by a 3 nm AlOx protection layer in air shows minimal degradation with stable QAH properties. Our work shows a route to preserve the dissipation-free chiral edge state in QAH devices for potential applications in quantum information technology.

Synthesis of nanostructured silver/silver halides on titanate surfaces and their visible-light photocatalytic performance.

Dense and uniform silver halides AgX (X = Cl, Br, I) nanoparticles were successfully fabricated on layered titanate nanowired honeycomb (TNHC) thin films. The growth of AgX nanocrystals was carried out through two steps. Firstly, ion-exchange was employed to incorporate Ag(+) ions into the interlayer of the titanate nanowires. Secondly, hydrogen halide (HX) solution was rapidly injected onto the ion-exchanged silver TNHC surface to generate nanosized AgX particles on TNHC films. The effect of the reaction time, solution pH, and concentration of halide anions on the morphology of the AgX photocatalysts has been studied. Followed by light-irradiation, the optimized Ag/AgX thin films exhibited excellent degradation performance under visible light because of localized surface plasmon resonance effect.