4,689 research outputs found
GABA\u3csub\u3eB\u3c/sub\u3e Receptor Attenuation of GABA\u3csub\u3eA\u3c/sub\u3e Currents in Neurons of the Mammalian Central Nervous System
Ionotropic receptors are tightly regulated by second messenger systems and are often present along with their metabotropic counterparts on a neuron\u27s plasma membrane. This leads to the hypothesis that the two receptor subtypes can interact, and indeed this has been observed in excitatory glutamate and inhibitory GABA receptors. In both systems the metabotropic pathway augments the ionotropic receptor response. However, we have found that the metabotropic GABAB receptor can suppress the ionotropic GABAA receptor current, in both the in vitro mouse retina and in human amygdala membrane fractions. Expression of amygdala membrane microdomains in Xenopus oocytes by microtransplantation produced functional ionotropic and metabotropic GABA receptors. Most GABAA receptors had properties of α‐subunit containing receptors, with ~5% having ρ‐subunit properties. Only GABAA receptors with α‐subunit‐like properties were regulated by GABAB receptors. In mouse retinal ganglion cells, where only α‐subunit‐containing GABAA receptors are expressed, GABAB receptors suppressed GABAA receptor currents. This suppression was blocked by GABAB receptor antagonists, G‐protein inhibitors, and GABAB receptor antibodies. Based on the kinetic differences between metabotropic and ionotropic receptors, their interaction would suppress repeated, rapid GABAergic inhibition
Intrinsic Percolative Superconductivity in KxFe2-ySe2 Single Crystals
Magnetic field penetration and magnetization hysteresis loops (MHLs) have
been measured in KxFe2-ySe2 single crystals. The magnetic field penetration
shows a two-step feature with a very small full-magnetic-penetration field
(Hp1= 300 Oe at 2 K), and accordingly the MHL exhibits an abnormal vanishing of
the central peak near zero field below 13 K. The width of the MHL in KxFe2-ySe2
at the same temperature is in general much smaller than that measured in the
relatives Ba0.6K0.4Fe2As2 and Ba(Fe0.92Co0.08)2As2, and the MHLs in the latter
two samples show the normal central peak near zero field. All these anomalies
found in KxFe2-ySe2 can be understood in the picture that the sample is
percolative with weakly coupled superconducting islands.Comment: 5 page, 4 figure
Superconductivity Near a Quantum Critical Point in Ba(Fe,Co)2As2
We will examine the possible link between spin fluctuations and the
superconducting mechanism in the iron-based high temperature superconductor
Ba(Fe,Co)2As2 based on NMR and high pressure transport measurements.Comment: Invited paper to m2s-IX (2009
Filamentary superconductivity across the phase diagram of Ba(Fe,Co)As
We show magnetotransport results on Ba(FeCo)As () single crystals. We identify the low temperature resistance step
at 23 K in the parent compound with the onset of filamentary superconductivity
(FLSC), which is suppressed by an applied magnetic field in a similar manner to
the suppression of bulk superconductivity (SC) in doped samples. FLSC is found
to persist across the phase diagram until the long range antiferromagnetic
order is completely suppressed. A significant suppression of FLSC occurs for
, the doping concentration where bulk SC emerges. Based on these
results and the recent report of an electronic anisotropy maximum for 0.02
0.04 [Science 329, 824 (2010)], we speculate that, besides spin
fluctuations, orbital fluctuations may also play an important role in the
emergence of SC in iron-based superconductors.Comment: 5 pages, 3 figure
Quantum Orders and Symmetric Spin Liquids
A concept -- quantum order -- is introduced to describe a new kind of orders
that generally appear in quantum states at zero temperature. Quantum orders
that characterize universality classes of quantum states (described by {\em
complex} ground state wave-functions) is much richer then classical orders that
characterize universality classes of finite temperature classical states
(described by {\em positive} probability distribution functions). The Landau's
theory for orders and phase transitions does not apply to quantum orders since
they cannot be described by broken symmetries and the associated order
parameters. We find projective representations of symmetry groups (which will
be called projective symmetry groups) can be used to characterize quantum
orders. With the help of quantum orders and the projective symmetry groups, we
construct hundreds of symmetric spin liquids, which have SU(2), U(1) or
gauge structures at low energies. Remarkably, some of the stable quantum phases
support gapless excitations even without any spontaneous symmetry breaking. We
propose that it is the quantum orders (instead of symmetries) that protect the
gapless excitations and make algebraic spin liquids and Fermi spin liquids
stable. Since high superconductors are likely to be described by a
gapless spin liquid, the quantum orders and their projective symmetry group
descriptions lay the foundation for spin liquid approach to high
superconductors.Comment: 58 pages, RevTeX4 home page: http://dao.mit.edu/~we
Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
Using two experimental techniques, we studied single crystals of the 122-FeAs
family with almost the same critical temperature, Tc. We investigated the
temperature dependence of the lower critical field of a single crystal under
static magnetic fields parallel to the axis. The temperature dependence of the
London penetration depth can be described equally well either by a single
anisotropic -wave-like gap or by a two-gap model, while a d-wave approach
cannot be used to fit the London penetration depth data. Intrinsic multiple
Andreev reflection effect spectroscopy was used to detect bulk gap values in
single crystals of the intimate compound, with the same Tc. We estimated the
range of the large gap value 6-8 meV (depending on small variation of and its a
space anisotropy of about 30%, and the small gap 1.7 meV. This clearly
indicates that the gap structure of our investigated systems more likely
corresponds to a nodeless s-wave two gaps.Comment: 9 pages, 6 figure
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