Ice nucleation at the contact line triggered by transient electrowetting fields

Supercooled water is found to have a significantly enhanced freezing temperature during transient electrowetting with electric fields of order 1 V/μm. High speed imaging reveals that the nucleation occurs randomly at the three-phase contact line (droplet perimeter) and can occur at multiple points during one freezing event. Possible nucleation mechanisms are explored by testing various substrate geometries and materials. Results demonstrate that electric field alone has no detectable effect on ice nucleation, but the moving boundary of the droplet on the substrate due to electrowetting is associated with the triggering of nucleation at a much higher temperature

Mesoscopic Transport of Quantum Anomalous Hall Effect in Sub-Micron Size Regime

The quantum anomalous Hall (QAH) effect has been demonstrated in two-dimensional topological insulator systems incorporated with ferromagnetism. However, a comprehensive understanding of mesoscopic transport in sub-micron QAH devices has yet been established. Here we fabricated miniaturized QAH devices with channel widths down to 600 nm, where the QAH features are still preserved. A back-scattering channel is formed in narrow QAH devices through percolative hopping between 2D compressible puddles. Large resistance fluctuations are observed in narrow devices near the coercive field, which is associated with collective interference between intersecting paths along domain walls when the device geometry is smaller than the phase coherence length $L_\phi$. Through measurement of size-dependent breakdown current, we confirmed that the chiral edge states are confined at the physical boundary with its width on the order of Fermi wavelength.Comment: 7 pages, 5 figure

Pressure tunable quantum anomalous Hall states in a topological antiferromagnet

Mechanical modulation of the lattice parameter can modify the electronic structure and manipulate the magnetic coupling of a material without introducing impurities. Inspired by success in pressure-controlled magnetism, we investigate the effect of hydrostatic pressure on quantized Chern states in the antiferromagnetic topological insulator MnBi2Te4, using transport as a probe. We show that pressure can enhance the robustness of quantum anomalous Hall (QAH) phases that are otherwise delicate in 7SL MnBi2Te4 and in the spin-flop (SF) state of 8SL MnBi2Te4. We explain our findings using a coupled Dirac cone model of MnBi2Te4, which identifies stronger hybridization between van der Waals layers as the driver of topological states. We further demonstrate that moderate pressures readily available in laboratory systems can provide reversible control of magnetic and topological phases. Our results reveal a strong connection between the mechanical engineering of band topology and magnetism.Comment: 11 pages, 4 figure

Distinguishing two-component anomalous Hall effect from topological Hall effect in magnetic topological insulator MnBi2Te4

In transport, the topological Hall effect (THE) is widely interpreted as a sign of chiral spin textures, like magnetic skyrmions. However, the co-existence of two anomalous Hall effects (AHE) could give rise to similar non-monotonic features or "humps", making it difficult to distinguish between the two. Here we demonstrate that the "artifact" two-component anomalous Hall effect can be clearly distinguished from the genuine topological Hall effect by three methods: 1. Minor loops 2. Temperature dependence 3. Gate dependence. One of the minor loops is a single loop that cannot fit into the full AHE loop under the assumption of AHE+THE. In addition, by increasing the temperature or tuning the gate bias, the emergence of humps is accompanied by a polarity change of the AHE. Using these three methods, one can find the humps are from another AHE loop with a different polarity. Our material is a magnetic topological insulator MnBi2Te4 grown by molecular beam epitaxy, where the presence of the secondary phase MnTe2 on the surface contributes to the extra positive AHE component. Our work may help future researchers to exercise cautions and use these three methods to examine carefully in order to ascertain genuine topological Hall effect

Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator

Topological insulators (TI) can apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization with their unique topological surface states, and their magnetic counterparts, magnetic topological insulators (MTI) offer magnetization without shunting and are one of the highest in SOT efficiency. Here, we demonstrate efficient SOT switching of a hard MTI, V-doped (Bi,Sb)2Te3 (VBST) with a large coercive field that can prevent the influence of an external magnetic field and a small magnetization to minimize stray field. A giant switched anomalous Hall resistance of 9.2 $k\Omega$ is realized, among the largest of all SOT systems. The SOT switching current density can be reduced to $2.8\times10^5 A/cm^2$, and the switching ratio can be enhanced to 60%. Moreover, as the Fermi level is moved away from the Dirac point by both gate and composition tuning, VBST exhibits a transition from edge-state-mediated to surface-state-mediated transport, thus enhancing the SOT effective field to $1.56\pm 0.12 T/ (10^6 A/cm^2)$ and the spin Hall angle to $23.2\pm 1.8$ at 5 K. The findings establish VBST as an extraordinary candidate for energy-efficient magnetic memory devices

A systematic evaluation of payback of publicly funded health and health services research in Hong Kong

<p>Abstract</p> <p>Background</p> <p>The Health and Health Services Research Fund (HHSRF) is dedicated to support research related to all aspects of health and health services in Hong Kong. We evaluated the fund's outcomes and explored factors associated with the translation of research findings to changes in health policy and provider behaviour.</p> <p>Methods</p> <p>A locally suitable questionnaire was developed based on the "payback" evaluation framework and was sent to principal investigators of the completed research projects supported by the fund since 1993. Research "payback" in six outcome areas was surveyed, namely knowledge production, use of research in the research system, use of research project findings in health system policy/decision making, application of the research findings through changed behaviour, factors influencing the utilization of research, and health/health service/economic benefits.</p> <p>Results</p> <p>Principal investigators of 178 of 205 (87%) completed research projects returned the questionnaire. Investigators reported research publications in 86.5% (mean = 5.4 publications per project), career advancement 34.3%, acquisition of higher qualifications 38.2%, use of results in policy making 35.4%, changed behaviour in light of findings 49.4%, evidence of health service benefit 42.1% and generated subsequent research in 44.9% of the projects. Payback outcomes were positively associated with the amount of funding awarded. Multivariate analysis found participation of investigators in policy committees and liaison with potential users were significantly associated with reported health service benefit (odds ratio [OR]_{participation}= 2.86, 95% confidence interval [CI] 1.28–6.40; OR_liaison= 2.03, 95% CI 1.05–3.91), policy and decision-making (OR_{participation}= 10.53, 95% CI 4.13–26.81; OR_liaison= 2.52, 95% CI 1.20–5.28), and change in behavior (OR_{participation}= 3.67, 95% CI 1.53–8.81).</p> <p>Conclusion</p> <p>The HHSRF has produced substantial outcomes and compared favourably with similar health research funds in other developed economies. Further studies are needed to better understand the factors and pathways associated with the translation of research findings into practice.</p