RESUMEN
Breaking time reversal symmetry in a topological insulator may lead to quantum anomalous Hall effect and axion insulator phase. MnBi4Te7 is a recently discovered antiferromagnetic topological insulator with TN â¼ 12.5 K, which is composed of an alternatively stacked magnetic layer (MnBi2Te4) and nonmagnetic layer (Bi2Te3). By means of scanning tunneling spectroscopy, we clearly observe the electronic state present at a step edge of a magnetic MnBi2Te4 layer but absent at nonmagnetic Bi2Te3 layers at 4.5 K. Furthermore, we find that as the temperature rises above TN the edge state vanishes, while the point defect induced state persists upon an increase in temperature. These results confirm the observation of magnetism-induced edge states. Our analysis based on an axion insulator theory reveals that the nontrivial topological nature of the observed edge state.
RESUMEN
A sufficiently large supercurrent can close the energy gap in a superconductor and create gapless quasiparticles through the Doppler shift of quasiparticle energy caused by finite Cooper pair momentum. In this gapless superconducting state, zero-energy quasiparticles reside on a segment of the normal-state Fermi surface, whereas the remaining Fermi surface is still gapped. We use quasiparticle interference to image the field-controlled Fermi surface of bismuth telluride (Bi2Te3) thin films under proximity effect from the superconductor niobium diselenide (NbSe2). A small applied in-plane magnetic field induces a screening supercurrent, which leads to finite-momentum pairing on the topological surface states of Bi2Te3. We identify distinct interference patterns that indicate a gapless superconducting state with a segmented Fermi surface. Our results reveal the strong impact of finite Cooper pair momentum on the quasiparticle spectrum.
RESUMEN
A capillary electrophoretic method with laser-induced fluorescence detection for baclofen (4-amino-3-p-chlorophenylbutyric acid) has been developed. 6-Carboxyfluorescein succinimidyl ester was used for precolumn derivatization of the non-fluorescent drug. Optimal separation and detection were obtained with an electrophoretic buffer of 50 mM sodium borate (pH 9.5) and an air-cooled argon-ion laser (excitation at 488 nm, emission at 520 nm). Linearity (r > or = 0.99) over three orders of magnitude was generally obtained and the lowest derivatizable concentration limit for baclofen in aqueous solution was 10 nM (2 ng baclofen/ml). Coupled with a simple clean up procedure, the method can be applied to the analysis of baclofen in human plasma at micromolar level. Recovery of spiked baclofen in plasma was 95%. The relative standard deviation values on peak size (0.5 microM level) and migration time were 8.2 and 1.0% (n=7), respectively. The limit of detection of baclofen in plasma was 0.1 microM (21 ng/ml).