Inter-band optical transitions of helical Majorana edge modes in topological superconductors

The search for evidence of Majorana states on the edges of topological superconductors (TSCs) is challenging due to the difficulty of detecting such charge-neutral electronic quasiparticles. Local microwave spectroscopy has been shown to be a possible method to detect propagating Majorana modes, where a spatially focused light beam must be used. Here, we show that helical Majorana modes in TSCs allow inter-band transitions and thus contribute to optical conductivity under a spatially uniform light. The existence of such a signal requires the system to break certain symmetries so that the projection of the charge current operator onto helical Majorana edge states leads to inter-band hybridization terms. The general form of this contribution under a tunable time-reversal breaking field is derived, which is valid in the sub-gap low-frequency regime where the edge energy spectrum is linear, and numerical results are obtained in three TSC models, showing remarkable consistency with the analytical prediction. In comparison, the current operator for normal helical edge states, such as in quantum spin Hall insulators, does not cause inter-band transitions and the related optical conductivity vanishes unless the time-reversal symmetry is broken. Our results may help guide feasible experiments to provide evidence of Majorana edge modes in TSCs.Comment: 4.5 pages, 5 figures + Appendi

The ρ\rho-meson longitudinal leading-twist distribution amplitude

In the present paper, we suggest a convenient model for the vector $\rho$-meson longitudinal leading-twist distribution amplitude $\phi_{2;\rho}^\|$, whose distribution is controlled by a single parameter $B^\|_{2;\rho}$. By choosing proper chiral current in the correlator, we obtain new light-cone sum rules (LCSR) for the $B\to\rho$ TFFs $A_1$, $A_2$ and $V$, in which the $\delta^1$-order $\phi_{2;\rho}^\|$ provides dominant contributions. Then we make a detailed discussion on the $\phi_{2;\rho}^\|$ properties via those $B\to\rho$ TFFs. A proper choice of $B^\|_{2;\rho}$ can make all the TFFs agree with the lattice QCD predictions. A prediction of $|V_{\rm ub}|$ has also been presented by using the extrapolated TFFs, which indicates that a larger $B^{\|}_{2;\rho}$ leads to a larger $|V_{\rm ub}|$. To compare with the BABAR data on $|V_{\rm ub}|$, the longitudinal leading-twist DA $\phi_{2;\rho}^\|$ prefers a doubly-humped behavior.Comment: 7 pages, 3 figures. Discussions improved and references updated. To be published in Phys.Lett.

An L1 image transform for edge-preserving smoothing and scene-level intrinsic decomposition

Identifying sparse salient structures from dense pixels is a longstanding problem in visual computing. Solutions to this problem can benefit both image manipulation and understanding. In this paper, we introduce an image transform based on the L1 norm for piecewise image flattening. This transform can effectively preserve and sharpen salient edges and contours while eliminating insignificant details, producing a nearly piecewise constant image with sparse structures. A variant of this image transform can perform edge-preserving smoothing more effectively than existing state-of-the-art algorithms. We further present a new method for complex scene-level intrinsic image decomposition. Our method relies on the above image transform to suppress surface shading variations, and perform probabilistic reflectance clustering on the flattened image instead of the original input image to achieve higher accuracy. Extensive testing on the Intrinsic-Images-in-the-Wild database indicates our method can perform significantly better than existing techniques both visually and numerically. The obtained intrinsic images have been successfully used in two applications, surface retexturing and 3D object compositing in photographs.postprin

Demonstration of Josephson effect submillimeter wave sources with increased power

This is the published version, also available here: http://dx.doi.org/10.1063/1.111904.A submillimeter wave source based on a new design using Josephson junction arrays has been developed and tested. The maximum rf power, delivered to a 68Ω load and detected on chip, was 47 μW at 394 GHz. Significant power was detected at a number of frequencies from 300 to 500 GHz where the power was 10 μW. The observed power at the designed operating frequency near 400 GHz is consistent with all 500 junctions in the series biased array delivering current in phase to the loads. This is in agreement with simulations of smaller arrays of the same design. The linewidth, inferred from the measured resistance at the point of maximum power, with T=4.2 K, is less than 1 MHz. The minimum inferred linewidth near 400 GHz, at somewhat lower power, is about 100 kHz

An fMRI study of grammatical morpheme processing associated with nouns and verbs in Chinese

This study examined whether the degree of complexity of a grammatical component in a language would impact on its representation in the brain through identifying the neural correlates of grammatical morpheme processing associated with nouns and verbs in Chinese. In particular, the processing of Chinese nominal classifiers and verbal aspect markers were investigated in a sentence completion task and a grammaticality judgment task to look for converging evidence. The Chinese language constitutes a special case because it has no inflectional morphology per se and a larger classifier than aspect marker inventory, contrary to the pattern of greater verbal than nominal paradigmatic complexity in most European languages. The functional imaging results showed BA47 and left supplementary motor area and superior medial frontal gyrus more strongly activated for classifier processing, and the left posterior middle temporal gyrus more responsive to aspect marker processing. We attributed the activation in the left prefrontal cortex to greater processing complexity during classifier selection, analogous to the accounts put forth for European languages, and the left posterior middle temporal gyrus to more demanding verb semantic processing. The overall findings significantly contribute to cross-linguistic observations of neural substrates underlying processing of grammatical morphemes from an analytic and a classifier language, and thereby deepen our understanding of neurobiology of human language.published_or_final_versio