Abstract
Magnetization plateaus in quantum magnets—where bosonic quasiparticles crystallize into emergent spin superlattices—are spectacular yet simple examples of collective quantum phenomena ...escaping classical description. While magnetization plateaus have been observed in a number of spin-1/2 antiferromagnets, the description of their magnetic excitations remains an open theoretical and experimental challenge. Here, we investigate the dynamical properties of the triangular-lattice spin-1/2 antiferromagnet Ba
3
CoSb
2
O
9
in its one-third magnetization plateau phase using a combination of nonlinear spin-wave theory and neutron scattering measurements. The agreement between our theoretical treatment and the experimental data demonstrates that magnons behave semiclassically in the plateau in spite of the purely quantum origin of the underlying magnetic structure. This allows for a quantitative determination of Ba
3
CoSb
2
O
9
exchange parameters. We discuss the implication of our results to the deviations from semiclassical behavior observed in zero-field spin dynamics of the same material and conclude they must have an intrinsic origin.
We report on a new constraint on gravitylike short-range forces, in which the interaction charge is mass, obtained by measuring the angular distribution of 5 Å neutrons scattering off atomic xenon ...gas. Around 10^{7} scattering events were collected at the 40 m small angle neutron scattering beam line located at the HANARO research reactor of the Korean Atomic Energy Research Institute. The extracted coupling strengths of new forces in the Yukawa-type parametrization are gover ^^{2}=(0.2±6.8±2.0)×10^{-15} GeV^{-2} and gover ^^{2}=(-5.3±9.0_{-2.8}^{+2.7})×10^{-17} GeV^{-2} for interaction ranges of 0.1 and 1.0 nm, respectively. These strengths correspond to 95% confidence level limits of g^{2}<(1.4±0.2)×10^{-14} GeV^{-2} and g^{2}<(1.3±0.2)×10^{-16} GeV^{-2}, improving the current limits for interaction ranges between 4 and 0.04 nm by a factor of up to 10.
Quantum fluctuations become particularly relevant in highly frustrated quantum magnets and can lead to new states of matter. We provide a simple and robust scenario for inducing magnetic vortex ...crystals in frustrated Mott insulators. By considering a quantum paramagnet that has a gapped spectrum with six-fold degenerate low-energy modes, we study the magnetic-field-induced condensation of these modes. We use a dilute gas approximation to demonstrate that a plethora of multi-Q condensates are stabilized for different combinations of exchange interactions. This rich quantum phase diagram includes magnetic vortex crystals, which are further stabilized by symmetric exchange anisotropies. Because skyrmion and domain-wall crystals have already been predicted and experimentally observed, this novel vortex phase completes the picture of emergent crystals of topologically nontrivial spin configurations.
We study a frustrated quantum Ising model relevant for Ca3Co2O6 that consists of a triangular lattice of weakly coupled ferromagnetic chains. According to our quantum Monte Carlo simulations, the ...chains become ferromagnetic and form a three-sublattice "up-up-down" structure for T≤T(CI). In contrast, long-wavelength spin-density-wave microphases are stabilized along the chains for T(CI)<T<T(c). Our mean field solutions reveal a quasicontinuous temperature dependence of the modulation wavelength, implying the existence of metastable states that explain the very slow dynamics observed in Ca3Co2O6. We also discuss implications of microphases for the related multiferroic compounds Ca3CoMnO6 and Lu2MnCoO6.
Abstract
The hippocampus is functionally heterogeneous between the dorsal and ventral subfields with left–right asymmetry. To determine the possible location of contextual memory, we performed an ...inhibitory avoidance task to analyze synaptic plasticity using slice patch-clamp technique. The training bilaterally increased the AMPA/NMDA ratio at dorsal CA3–CA1 synapses, whereas the training did not affect the ratio at ventral CA3–CA1 synapses regardless of the hemisphere. Moreover, sequential recording of miniature excitatory postsynaptic currents and miniature inhibitory postsynaptic currents from the same CA1 neuron clearly showed learning-induced synaptic plasticity. In dorsal CA1 neurons, the training dramatically strengthened both excitatory and inhibitory postsynaptic responses in both hemispheres, whereas the training did not promote the plasticity in either hemisphere in ventral CA1 neurons. Nonstationary fluctuation analysis further revealed that the training bilaterally increased the number of AMPA or GABAA receptor channels at dorsal CA1 synapses, but not at ventral CA1 synapses, suggesting functional heterogeneity of learning-induced receptor mobility. Finally, the performance clearly impaired by the bilateral microinjection of plasticity blockers in dorsal, but not ventral CA1 subfields, suggesting a crucial role for contextual learning. The quantification of synaptic diversity in specified CA1 subfields may help us to diagnose and evaluate cognitive disorders at the information level.
Ultracold neutrons (UCNs) can be bound by the potential of terrestrial gravity and a reflecting mirror. The wave function of the bound state has characteristic modulations. We carried out an ...experiment to observe the vertical distribution of the UCNs above such a mirror at the Institut Laue-Langevin in 2011. The observed modulation is in good agreement with that prediction by quantum mechanics using the Wigner function. The spatial resolution of the detector system is estimated to be 0.7 μm. This is the first observation of gravitationally bound states of UCNs with submicron spatial resolution.
Abstract Patients with long-standing diabetes commonly develop diabetic encephalopathy, which is characterized by cognitive impairment and dementia. Oxidative stress–induced neuronal cell apoptosis ...is a contributing factor. Glucagon-like peptide (GLP)-1 has recently become an attractive treatment modality for patients with diabetes. It also readily enters the brain, prevents neuronal cell apoptosis, and improves the cognitive impairment characteristic of Alzheimer's disease. Therefore, we investigated whether GLP-1 could protect against oxidative stress–induced neuronal cell apoptosis in pheochromocytoma (PC12) cells. PC12 cells were exposed to 1 mM methylglyoxal (MG) or MG plus 3.30 μg/ml GLP-1. Cell apoptosis, expression and phosphorylation of phosphatidylinositol-3 kinase/Akt/mammalian target of rapamycin/γ-glutamylcysteine ligase catalytic subunit (GCLc), and redox balance were then determined. The data showed that MG induced PC12 apoptosis in accordance with the redox (glutathione (GSH) and GSH/glutathione disulfide GSSG) imbalance. GLP-1 protected against this MG-induced apoptosis, which corresponded to the phosphorylation of PI3K, Akt, and mTOR, as well as the upregulation of GCLc and the restoration of the redox imbalance. Inhibitors of PI3K ( LY294002 ), Akt (Akt-I), and mTOR (rapamycin) reduced the GLP-1-induced GCLc upregulation and its protection against MG-induced PC12 apoptosis. The GLP-1-induced redox restoration was also attenuated by rapamycin. In conclusion, the neuroprotective effect of GLP-1 is due to an enhancement of PI3K/Akt/mTOR/GCLc/redox signaling.
We study the spin-S Kitaev model in the classical (S→∞) limit using Monte Carlo simulations combined with semiclassical spin dynamics. We discuss differences and similarities in the dynamical ...structure factors of the spin-1/2 and the classical Kitaev liquids. The quantum behavior is restricted to low temperatures where a gap protects visons from decohering the system. Once this quantum gap is breached, at low temperatures compared to the coupling constant, significant entropic disorder decoheres the Majorana fermions and the system is described quantitatively by classical dynamics. The low-temperature and low-energy spectrum of the classical model exhibits a finite-energy peak, which is the precursor of the one produced by the Majorana modes of the S=1/2 model. The classical peak is spectrally narrowed compared to the quantum result and can be explained by magnon excitations within fluctuating one-dimensional manifolds (loops). Hence the difference from the classical limit to the quantum limit can be understood by the fractionalization of magnons propagating in one-dimensional manifolds. Moreover, we show that the momentum-space distribution of the low-energy spectral weight of the S=1/2 model follows the momentum-space distribution of zero modes of the classical model.
We demonstrate multiferroic behavior in trimerized Mott insulators through the interplay between spins and electric dipole moments resulting from electronic charge fluctuations in frustrated units. ...The model consists of stacked triangular layers of trimers with small intertrimer exchange interactions J' and J''. Ferroelectric states coexist with ferro- or antiferromagnetic orderings depending on the value of the magnetic field H and the sign of the interlayer exchange J''. The electric polarization undergoes abrupt changes as a function of H.
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