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Decoupling of the graphene layer from the ferromagnetic substrate via intercalation of sp metal has recently been proposed as an effective way to realize single-layer graphene-based spin-filter. Here, the structural and electronic properties of the prototype system, graphene/Al/Ni(111), are investigated via combination of electron diffraction and spectroscopic methods. These studies are accompanied by state-of-the-art electronic structure calculations. The properties of this prospective Al-intercalation-like system and its possible implementations in future graphene-based devices are discussed., Comment: 20 pages, 8 figures, and supplementary material

Here we present an angle-resolved photoelectron spectroscopy (ARPES), x-ray absorption spec-troscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia ad-sorption on graphene/Ni(111). Our results on graphene/Ni(111) reveal the existence of interface states, originating from the strong hybridization of the graphene {\pi} and spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information about the kind of interaction between adsorbed molecules and graphene on Ni(111). The presented experimental data are compared with the results obtained in the framework of the DFT approach., Comment: accepted in Nanoscale Research Letters; 16 pages, 4 figures, 2 tables

The bond-percolation properties of the Hanoi networks are analyzed with the renormalization group. Unlike scale-free networks, they are meant to provide an analytically tractable interpolation between finite dimensional, lattice-based models and their mean-field limits. In percolation, the hierarchical small-world bonds in the Hanoi networks impose a new form of order by uniting otherwise disconnected, local clusters. This "patchy" order results in merely a finite probability to obtain a spanning cluster for certain ranges of the bond probability, unlike the usual 0-1 transition found on ordinary lattices. The various networks studied here exhibit a range of phase behaviors, depending on the prevalence of those long-range bonds. Fixed points in general exhibit non-universal behavior., Comment: 12 pages, revtex, 15 figures, find related papers at http://www.physics.emory.edu/faculty/boettcher/

The stiffness exponents in the glass phase for lattice spin glasses in dimensions $d=3,...,6$ are determined. To this end, we consider bond-diluted lattices near the T=0 glass transition point $p^*$. This transition for discrete bond distributions occurs just above the bond percolation point $p_c$ in each dimension. Numerics suggests that both points, $p_c$ and $p^*$, seem to share the same $1/d$-expansion, at least for several leading orders, each starting with $1/(2d)$. Hence, these lattice graphs have average connectivities of $\alpha=2dp\gtrsim1$ near $p^*$ and exact graph-reduction methods become very effective in eliminating recursively all spins of connectivity $\leq3$, allowing the treatment of lattices of lengths up to L=30 and with up to $10^5-10^6$ spins. Using finite-size scaling, data for the defect energy width $\sigma(\Delta E)$ over a range of $p>p^*$ in each dimension can be combined to reach scaling regimes of about one decade in the scaling variable $L(p-p^*)^{\nu^*}$. Accordingly, unprecedented accuracy is obtained for the stiffness exponents compared to undiluted lattices ($p=1$), where scaling is far more limited. Surprisingly, scaling corrections typically are more benign for diluted lattices. We find in $d=3,...,6$ for the stiffness exponents $y_3=0.24(1)$, $y_4=0.61(2), y_5=0.88(5)$, and $y_6=1.1(1)$. The result for the upper critical dimension, $d_u=6$, suggest a mean-field value of $y_\infty=1$., Comment: 8 pages, RevTex, 15 ps-figures included (see http://www.physics.emory.edu/faculty/boettcher for related information)

Numerical results are presented indicating d_c=4 as the upper critical dimension for the Bak-Sneppen evolution model. This finding agrees with previous theoretical arguments, but contradicts a recent Letter [Phys. Rev. Lett. 80, 5746-5749 (1998)] that placed d_c as high as d=8. In particular, we find that avalanches are compact for all dimensions d4. Under those conditions, scaling arguments predict a d_c=4, where hyperscaling relations hold for d, 4 pages, RevTex4, as to appear in Phys. Rev. Lett., related papers available at http://userwww.service.emory.edu/~sboettc/

A difficult and long-standing problem in mathematical physics concerns the determination of the value of $f(\infty)$ from the asymptotic series for $f(x)$ about $x\!=\!0$. In the past the approach has been to convert the asymptotic series to a sequence of Pad\'e approximants $\{P^n_n(x)\}$ and then to evaluate these approximants at $x\!=\!\infty$. Unfortunately, for most physical applications the sequence $\{P^n_n(\infty)\}$ is slowly converging and does not usually give very accurate results. In this paper we report the results of extensive numerical studies for a large class of functions $f(x)$ associated with strong-coupling lattice approximations. We conjecture that for large $n$, $P^n_n(\infty)\!\sim\!f(\infty)+B/\ln n $. A numerical fit to this asymptotic behavior gives an accurate extrapolation to the value of $f(\infty )$., Comment: plain TEX, 7 pages, 7 figures included, WASH-U-HEP-93