202 research outputs found
Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid
The quantum Hall effect (QHE) in two-dimensional (2D) electron gases, which
is one of the most striking phenomena in condensed matter physics, involves the
topologically protected dissipationless charge current flow along the edges of
the sample. Integer or fractional electrical conductance are measured in units
of , which is associated with edge currents of electrons or
quasiparticles with fractional charges, respectively. Here we discover a novel
type of quantization of the Hall effect in an insulating 2D quantum magnet. In
-RuCl with dominant Kitaev interaction on 2D honeycomb lattice, the
application of a parallel magnetic field destroys the long-range magnetic
order, leading to a field-induced quantum spin liquid (QSL) ground state with
massive entanglement of local spins. In the low-temperature regime of the QSL
state, we report that the 2D thermal Hall conductance
reaches a quantum plateau as a function of applied magnetic field.
attains a quantization value of ,
which is exactly half of in the integer QHE. This
half-integer thermal Hall conductance observed in a bulk material is a direct
signature of topologically protected chiral edge currents of charge neutral
Majorana fermions, particles that are their own antiparticles, which possess
half degrees of freedom of conventional fermions. These signatures demonstrate
the fractionalization of spins into itinerant Majorana fermions and
fluxes predicted in a Kitaev QSL. Above a critical magnetic field, the
quantization disappears and goes to zero rapidly,
indicating a topological quantum phase transition between the states with and
without chiral Majorana edge modes. Emergent Majorana fermions in a quantum
magnet are expected to have a major impact on strongly correlated topological
quantum matter.Comment: 7 pages, 8 figures. Submitted versio
Inter-planar coupling dependent magnetoresistivity in high purity layered metals
The magnetic field-induced changes in the conductivity of metals are the
subject of intense interest, both for revealing new phenomena and as a valuable
tool for determining their Fermi surface. Here, we report a hitherto unobserved
magnetoresistive effect in ultra-clean layered metals, namely a negative
longitudinal magnetoresistance that is capable of overcoming their very
pronounced orbital one. This effect is correlated with the inter-layer coupling
disappearing for fields applied along the so-called Yamaji angles where the
inter-layer coupling vanishes. Therefore, it is intrinsically associated with
the Fermi points in the field-induced quasi-one-dimensional electronic
dispersion, implying that it results from the axial anomaly among these Fermi
points. In its original formulation, the anomaly is predicted to violate
separate number conservation laws for left- and right-handed chiral- (e.g.
Weyl) fermions. Its observation in PdCoO, PtCoO and SrRuO
suggests that the anomaly affects the transport of clean conductors,
particularly near the quantum limit.Comment: Nature Communications (in press
A novel platform to enable the high-throughput derivation and characterization of feeder-free human iPSCs
Human induced pluripotent stem cells (hiPSCs) hold enormous potential, however several obstacles impede their translation to industrial and clinical applications. Here we describe a platform to efficiently generate, characterize and maintain single cell and feeder-free (FF) cultured hiPSCs by means of a small molecule cocktail media additive. Using this strategy we have developed an effective multiplex sorting and high-throughput selection platform where individual clonal hiPSC lines are readily obtained from a pool of candidate clones, expanded and thoroughly characterized. By promoting survival and self-renewal, the selected hiPSC clones can be rapidly expanded over multiple FF, single-cell passages while maintaining their pluripotency and genomic stability as demonstrated by trilineage differentiation, karyotype and copy number variation analysis. This study provides a robust platform that increases efficiency, throughput, scale and quality of hiPSC generation and facilitates the industrial and clinical use of iPSC technology
Preferential Entry of Botulinum Neurotoxin A Hc Domain through Intestinal Crypt Cells and Targeting to Cholinergic Neurons of the Mouse Intestine
Botulism, characterized by flaccid paralysis, commonly results from botulinum neurotoxin (BoNT) absorption across the epithelial barrier from the digestive tract and then dissemination through the blood circulation to target autonomic and motor nerve terminals. The trafficking pathway of BoNT/A passage through the intestinal barrier is not yet fully understood. We report that intralumenal administration of purified BoNT/A into mouse ileum segment impaired spontaneous muscle contractions and abolished the smooth muscle contractions evoked by electric field stimulation. Entry of BoNT/A into the mouse upper small intestine was monitored with fluorescent HcA (half C-terminal domain of heavy chain) which interacts with cell surface receptor(s). We show that HcA preferentially recognizes a subset of neuroendocrine intestinal crypt cells, which probably represent the entry site of the toxin through the intestinal barrier, then targets specific neurons in the submucosa and later (90β120 min) in the musculosa. HcA mainly binds to certain cholinergic neurons of both submucosal and myenteric plexuses, but also recognizes, although to a lower extent, other neuronal cells including glutamatergic and serotoninergic neurons in the submucosa. Intestinal cholinergic neuron targeting by HcA could account for the inhibition of intestinal peristaltism and secretion observed in botulism, but the consequences of the targeting to non-cholinergic neurons remains to be determined
Trypanosoma cruzi Epimastigotes Are Able to Store and Mobilize High Amounts of Cholesterol in Reservosome Lipid Inclusions
Reservosomes are lysosome-related organelles found in Trypanosoma cruzi epimastigotes. They represent the last step in epimastigote endocytic route, accumulating a set of proteins and enzymes related to protein digestion and lipid metabolism. The reservosome matrix contains planar membranes, vesicles and lipid inclusions. Some of the latter may assume rectangular or sword-shaped crystalloid forms surrounded by a phospholipid monolayer, resembling the cholesterol crystals in foam cells.Using Nile Red fluorimetry and fluorescence microscopy, as well as electron microscopy, we have established a direct correlation between serum concentration in culture medium and the presence of crystalloid lipid inclusions. Starting from a reservosome purified fraction, we have developed a fractionation protocol to isolate lipid inclusions. Gas-chromatography mass-spectrometry (GC-MS) analysis revealed that lipid inclusions are composed mainly by cholesterol and cholesterol esters. Moreover, when the parasites with crystalloid lipid-loaded reservosomes were maintained in serum free medium for 48 hours the inclusions disappeared almost completely, including the sword shaped ones.Taken together, our results suggest that epimastigote forms of T. cruzi store high amounts of neutral lipids from extracellular medium, mostly cholesterol or cholesterol esters inside reservosomes. Interestingly, the parasites are able to disassemble the reservosome cholesterol crystalloid inclusions when submitted to serum starvation
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