Majorana Fermion Induced Resonant Andreev Reflection

We describe experimental signatures of Majorana fermion edge states, which form at the interface between a superconductor and the surface of a topological insulator. If a lead couples to the Majorana fermions through electron tunneling, the Majorana fermions induce \textit{resonant} Andreev reflections from the lead to the grounded superconductor. The linear tunneling conductance is $0$ ($2 e^2/h$) if there is an even (odd) number of vortices in the superconductor. Similar resonance occurs for tunneling into the zero mode in the vortex core. We also study the current and noise of a two-lead device.Comment: 4 pages, 3 figures. Discussion on STM tunneling into the Majorana zero mode in the vortex core is adde

Comparisons of soil suction induced by evapotranspiration and transpiration of S. <i>heptaphylla</i>

For a given evapotranspiration (ETr), both soil evaporation and plant transpiration (Tr) would induce soil suction. However, the relative contribution of these two processes to the amount of suction induced is not clear. The objective of this study is to quantify ETr- and Tr-induced suction by a selected tree species, Scheffllera heptaphylla, in silty sand. The relative contribution of transpiration and evaporation to the responses of suction is then explored based on observed differences in Tr- and ETr-induced suction. In total, 12 test boxes were used for testing: 10 for vegetated soil with different values of leaf area index (LAI) and root area index (RAI), while two were for bare soil as references. Each box was exposed to identical atmospheric conditions controlled in a plant room for monitoring suction responses over a week. Due to the additional effects of soil evaporation, ETr-induced suction could be 3%–47% higher than Tr-induced suction, depending on LAI. The significance of evaporation reduced substantially when LAI was higher, as relatively less radiant energy fell on the soil surface for evaporation. For a given LAI, the effects of evaporation were less significant at deeper depths within the root zone. The effects of RAI associated with root-water uptake upon transpiration were the dominant process of ETr affecting the suction responses.</jats:p

Supersolid phase in spin dimer XXZ systems under magnetic field

Using quantum Monte Carlo method, we study, under external magnetic fields, the ground state phase diagram of the two-dimensional spin $S$=1/2 dimer model with an anisotropic intra-plane antiferromagnetic coupling. With the anisotropy $4 \gtrsim \Delta \gtrsim 3$, a supersolid phase characterized by a non-uniform bose condensate density that breaks translational symmetry is found. The rich phase diagram also contains a checkerboard solid and two different types of superfluid phase formed by $S_z=+1$ and $S_z=0$ spin triplets, with finite staggered magnetization in z-axis and in-plane direction, respectively. As we show, the model can be realized as a consequence of including the next nearest neighbor coupling among dimers and our results suggest that spin dimer systems may be an ideal model system to study the supersolid phase.Comment: 4 pages, 5 figure

Probing the Galaxy I. The galactic structure towards the galactic pole

Observations of (B-V) colour distributions towards the galactic poles are compared with those obtained from synthetic colour-magnitude diagrams to determine the major constituents in the disc and spheroid. The disc is described with four stellar sub-populations: the young, intermediate, old, and thick disc populations, which have respectively scale heights of 100 pc, 250 pc, 0.5 kpc, and 1.0 kpc. The spheroid is described with stellar contributions from the bulge and halo. The bulge is not well constrained with the data analyzed in this study. A non-flattened power-law describes the observed distributions at fainter magnitudes better than a deprojected R^{1/4}-law. Details about the age, metallicity, and normalizations are listed in Table 1. The star counts and the colour distributions from the stars in the intermediate fields towards the galactic anti-centre are well described with the stellar populations mentioned above. Arguments are given that the actual solar offset is about 15 pc north from the galactic plane.Comment: 11 pages TeX, 4 separate pages with additional figures, accepted for publication in A&

Selective Equal-Spin Andreev Reflections Induced by Majorana Fermions

In this work, we find that Majorana fermions induce selective equal spin Andreev reflections (SESARs), in which incoming electrons with certain spin polarization in the lead are reflected as counter propagating holes with the same spin. The spin polarization direction of the electrons of this Andreev reflected channel is selected by the Majorana fermions. Moreover, electrons with opposite spin polarization are always reflected as electrons with unchanged spin. As a result, the charge current in the lead is spin-polarized. Therefore, a topological superconductor which supports Majorana fermions can be used as a novel device to create fully spin-polarized currents in paramagnetic leads. We point out that SESARs can also be used to detect Majorana fermions in topological superconductors.Comment: 5 pages, 3 figures. Comments are welcome. Title changed to match published versio

[CI], [CII] and CO emission lines as a probe for alpha variations at low and high redshifts

The offsets between the radial velocities of the rotational transitions of carbon monoxide and the fine structure transitions of neutral and singly ionized carbon are used to test the hypothetical variation of the fine structure constant, alpha. From the analysis of the [CI] and [CII] fine structure lines and low J rotational lines of 12CO and 13CO, emitted by the dark cloud L1599B in the Milky Way disk, we find no evidence for fractional changes in alpha at the level of |$\Delta \alpha/\alpha$| < 3*10^-7. For the neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from observations of three HII zones in [CII] and CO emission lines: |$\Delta \alpha/\alpha$| < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4, showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on |$\Delta \alpha/\alpha$| < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO emission lines turns out to be a powerful tool for probing the stability of the fundamental physical constants over a wide range of redshifts not accessible to optical spectral measurements.Comment: 10 pages, 3 figures, 5 tables. Accepted for publication in MNRA

The Ratio of Total to Selective Extinction Toward Baade's Window

We measure the ratio of total to selective extinction, R_{VI}=A_V/E(V-I), toward Baade's Window by comparing the VIK colors of 132 Baade's Window G and K giants from Tiede, Frogel, & Terndrup with the solar-neighborhood (V-I),(V-K) relation from Bessell & Brett. We find R_{VI}=2.283 +/- 0.016, and show that our measurement has no significant dependence on stellar type from G0 to K4. Adjusting the Paczynski et al. determination of the centroid of the dereddened Baade's Window clump for this revised value of $R_{VI}$, we find I_{0,RC}=14.43 and (V-I)_{0,RC}=1.058. This implies a distance to the Baade's Window clump of d_{BW} = 8.63 +/- 0.16 kpc, where the error bar takes account of statistical but not systematic uncertainties.Comment: 8 pages, 1 figure, submitted to Ap

Proximity fingerprint of s+- superconductivity

We suggest a straightforward and unambiguous test to identify possible opposite signs of superconducting order parameter in different bands proposed for iron-based superconductors (s+- state). We consider proximity effect in a weakly coupled sandwich composed of a s+- superconductor and thin layer of s-wave superconductor. In such system the s-wave order parameter is coupled differently with different s+- gaps and it typically aligns with one of these gaps. This forces the other s+- gap to be anti-aligned with the s-wave gap. In such situation the aligned band induces a peak in the s-wave density of states (DoS), while the anti-aligned band induces a dip. Observation of such contact-induced negative feature in the s-wave DoS would provide a definite proof for s+- superconductivity.Comment: 4 pages, one figur