EPR spectrum via entangled states for an Exchange-Coupled Dimer of Single-Molecule Magnets

Multi-high-frequency electron paramagnetic resonance(EPR) spectrum for a supermolecular dimer $[ Mn_4]_2$ of single-molecule magnets recently reported [S. Hill, R. S. Edwards, N. Aliaga-Alcalde and G. Christou(HEAC), Science 302, 1015 (2003)] is studied in terms of the perturbation method in which the high-order corrections to the level splittings of degenerate states are included. It is shown that the corresponding eigenvectors are composed of entangled states of two molecules. The EPR-peak positions are calculated in terms of the eigenstates at various frequencies. From the best fit of theoretical level splittings with the measured values we obtain the anisotropy constant and exchange coupling which are in agreement with the corresponding values of experimental observation. Our study confirms the prediction of HEAC that the two $Mn_4$ units within the dimer are coupled quantum mechanically by the antiferromagnetic exchange interaction and the supermolecular dimer behaviors in analogy with artificially fabricated quantum dots.Comment: 16 pages,2 figures, 2 table

Optical responses in two-dimensional tilted semi-Dirac bands

Within linear response theory, the absorptive part of optical conductivities are analytically calculated for distinct tilts in two-dimensional (2D) tilted semi-Dirac bands (TSDBs). The transverse optical conductivities always vanish $\mathrm{Re}\sigma_{xy}(\omega)=\mathrm{Re}\sigma_{yx}(\omega)=0$. The interband longitudinal optical conductivities (LOCs) in 2D TSDBs differ qualitatively in the power-law scaling of $\omega$ as $\mathrm{Re}\sigma_{xx}^{\mathrm{IB}}(\omega)\propto\sigma_0\sqrt{\omega}$ and $\mathrm{Re}\sigma_{yy}^{\mathrm{IB}}(\omega)\propto\sigma_0/\sqrt{\omega}$. By contrast, the intraband LOCs in 2D TSDBs depend on $\mu$ in the power-law scaling $\mathrm{Re}\sigma_{xx}^{\mathrm{D}}(\omega)\propto\sigma_0\mu \sqrt{\mu}$ and $\mathrm{Re}\sigma_{yy}^{\mathrm{D}}(\omega)\propto\sigma_0\mu/\sqrt{\mu}$. The power-law scaling is similar to that in 2D untilted SDBs but distincts from a uniform behavior independent of $\omega$ (or $\mu$) as $\mathrm{Re}\sigma_{xx/yy}^{\mathrm{IB}}(\omega)\propto\sigma_0$ (or $\mathrm{Re}\sigma_{xx/yy}^{\mathrm{D}}(\omega)\propto\sigma_0\mu$) in 2D tilted Dirac bands (TDBs). The universal power-law scaling further dictates significant differences in the angular dependence of LOCs, which can be used to characterize 2D TSDBs from 2D TDBs in the optical measurements. The tilt-dependent behaviors of LOCs can qualitatively tell 2D TSDBs from 2D untilted SDBs, but show similarities in the impact of band tilting between 2D TSDBs and 2D TDBs.Comment: 16 pages, 3 figure

Distinct distributed patterns of neural activity are associated with two languages in the bilingual brain

A large body of previous neuroimaging studies suggests that multiple languages are processed and organized in a single neuroanatomical system in the bilingual brain, although differential activation may be seen in some studies because of different proficiency levels and/or age of acquisition of the two languages. However, one important possibility is that the two languages may involve interleaved but functionally independent neural populations within a given cortical region, and thus, distinct patterns of neural computations may be pivotal for the processing of the two languages. Using functional magnetic resonance imaging (fMRI) and multivariate pattern analyses, we tested this possibility in Chinese-English bilinguals when they performed an implicit reading task. We found a broad network of regions wherein the two languages evoked different patterns of activity, with only partially overlapping patterns of voxels in a given region. These regions, including the middle occipital cortices, fusiform gyri, and lateral temporal, temporoparietal, and prefrontal cortices, are associated with multiple aspects of language processing. The results suggest the functional independence of neural computations underlying the representations of different languages in bilinguals

Antitumor Activity of cGAMP via Stimulation of cGAS-cGAMP-STING-IRF3 Mediated Innate Immune Response

Immunotherapy is one of the key strategies for cancer treatment. The cGAS-cGAMP-STING-IRF3 pathway of cytosolic DNA sensing plays a pivotal role in antiviral defense. We report that the STING activator cGAMP possesses significant antitumor activity in mice by triggering the STING-dependent pathway directly. cGAMP enhances innate immune responses by inducing production of cytokines such as interferon-β, interferon-γ, and stimulating dendritic cells activation, which induces the cross-priming of CD8(+) T cells. The antitumor mechanism of cGAMP was verified by STING and IRF3, which were up-regulated upon cGAMP treatment. STING-deficiency dramatically reduced the antitumor effect of cGAMP. Furthermore, cGAMP improved the antitumor activity of 5-FU, and clearly reduced the toxicity of 5-FU. These results demonstrated that cGAMP is a novel antitumor agent and has potential applications in cancer immunotherapy

Anomalous acoustic plasmons in two-dimensional over-tilted Dirac bands

The over-tilting of type-II Dirac cones has led to various fascinating quantum phenomena. Here we find two anomalous acoustic plasmons (AAPs) are dictated by the distinct geometry of two-dimensional (2D) type-II Dirac cones, far beyond the conventional \text{\ensuremath{\sqrt{q}}} plasmon. One AAP originates from the strong hybridization of two pockets at one Dirac point, whereas the other is attributed to the significant enhancement of the band correlation around the open Fermi surface. Remarkably, the plasmons exhibit valley-dependent chirality along the tilting direction due to the chiral electron dispersion. Meanwhile, we discuss the tunability of plasmon dispersion and lifetime by tuning the gap and dielectric substrate. Our work provides a promising way to generate the novel plasmons in Dirac materials.Comment: 6 pages, 5 figure

Longitudinal optical conductivities in tilted Dirac bands

We report a unified theory based on linear response, for analyzing the longitudinal optical conductivity (LOC) of materials with tilted Dirac cones. Depending on the tilt parameter $t$, the Dirac electrons have four phases, untilted, type-I, type-II, and type-III; the Dirac dispersion can be isotropic or anisotropic; the spatial dimension of the material can be one-, two-, or three-dimensions. The interband LOCs and intraband LOCs in $d$ dimension (with $d\ge2$) are found to scale as to $\sigma_{0}\omega^{d-2}$ and $\sigma_{0}|\mu|^{d-1}\delta(\omega)$, respectively, where $\omega$ is the frequency and $\mu$ the chemical potential. The interband LOCs always vanish in one dimension due to lacking of extra spatial dimension. The angular dependence of LOCs is found to characterize the band tilting, and the constant asymptotic background values of LOC reflect features of the Dirac bands. The LOCs in the anisotropic tilted Dirac cone can be connected to its isotropic counterpart by a ratio that consists of Fermi velocities. The findings are valid for a great many Dirac materials in the spatial dimensions of physical interests.Comment: 11 pages, 3 figure