Effects of electron scattering on the topological properties of nanowires: Majorana fermions from disorder and superlattices

We focus on inducing topological state from regular, or irregular scattering in (i) p-wave superconducting wires and (ii) Rashba wires proximity coupled to an s-wave superconductor. We find that contrary to common expectations the topological properties of both systems are fundamentally different: In p-wave wires, disorder generally has a detrimental effect on the topological order and the topological state is destroyed beyond a critical disorder strength. In contrast, in Rashba wires, which are relevant for recent experiments, disorder can {\it induce} topological order, reducing the need for quasiballistic samples to obtain Majorana fermions. Moreover, we find that the total phase space area of the topological state is conserved for long disordered Rashba wires, and can even be increased in an appropriately engineered superlattice potential.Comment: 5 pages, 3 figs, RevTe

Robustness of edge states in graphene quantum dots

We analyze the single particle states at the edges of disordered graphene quantum dots. We show that generic graphene quantum dots support a number of edge states proportional to circumference of the dot over the lattice constant. Our analytical theory agrees well with numerical simulations. Perturbations breaking electron-hole symmetry like next-nearest neighbor hopping or edge impurities shift the edge states away from zero energy but do not change their total amount. We discuss the possibility of detecting the edge states in an antidot array and provide an upper bound on the magnetic moment of a graphene dot.Comment: Added figure 6, extended discussion (version as accepted by Physical Review B

One-loop surface tensions of (supersymmetric) kink domain walls from dimensional regularization

We consider domain walls obtained by embedding the 1+1-dimensional $\phi^4$-kink in higher dimensions. We show that a suitably adapted dimensional regularization method avoids the intricacies found in other regularization schemes in both supersymmetric and non-supersymmetric theories. This method allows us to calculate the one-loop quantum mass of kinks and surface tensions of kink domain walls in a very simple manner, yielding a compact d-dimensional formula which reproduces many of the previous results in the literature. Among the new results is the nontrivial one-loop correction to the surface tension of a 2+1 dimensional N=1 supersymmetric kink domain wall with chiral domain-wall fermions.Comment: 23 pages, LATeX; v2: 25 pages, 2 references added, extended discussion of renormalization schemes which dispels apparent contradiction with previous result

Graphene Rings in Magnetic Fields: Aharonov-Bohm Effect and Valley Splitting

We study the conductance of mesoscopic graphene rings in the presence of a perpendicular magnetic field by means of numerical calculations based on a tight-binding model. First, we consider the magnetoconductance of such rings and observe the Aharonov-Bohm effect. We investigate different regimes of the magnetic flux up to the quantum Hall regime, where the Aharonov-Bohm oscillations are suppressed. Results for both clean (ballistic) and disordered (diffusive) rings are presented. Second, we study rings with smooth mass boundary that are weakly coupled to leads. We show that the valley degeneracy of the eigenstates in closed graphene rings can be lifted by a small magnetic flux, and that this lifting can be observed in the transport properties of the system.Comment: 12 pages, 9 figure

Is the Use of Honey an Effective Dressing Option for the Treatment of Diabetic Foot Ulcers?

OBJECTIVE: The objective of this systematic review is to determine whether or not honey could be used as an effective topical treatment for diabetic foot ulcers in diabetic patients.STUDY DESIGN: Review of three primary journal articles published in English between the years of 2008 and 2010.DATA SOURCES: Two Randomized Controlled Trials comparing honey as a treatment for diabetic foot ulcers to either previous failed treatments or Povidone Iodine Solution, and a pilot prospective study, exploring the effectiveness of PEDYPHAR a royal jelly ointment. All articles were found using Pubmed, OVID and Cochrane Database.OUTCOMES MEASURED: Healing time and percent of patients to reach wound closure or a state of healing ready for surgical closure was assessed in all of the studies. Healing was assessed by surgeons and was determined based on size of the ulcer and change in grade and stage using either the University of Texas Diabetic Wound Classification or the Wagner Classification, inflammation, presence of bacterial cultures and, presence of exudate.RESULTS: The Shukrimi et al. study showed that honey used as a dressing for diabetic foot ulcers was as effective as the control group using Povidone Iodine in days for healing. Moghazy et al. demonstrated that honey used on different stages of diabetic foot ulcers was effective at providing healing in a relatively short duration. The pilot prospective study by Abdelatif et al. also portrayed efficient healing with the use of PEDYPHAR and healing time was completed in a timely manner. The only side affect noted in the three studies was in the pilot prospective study. Four patients encountered mild burning with application of the PEDYPHAR ointment, but still continued with its use.CONCLUSIONS: All studies showed that honey was effective in allowing for healing improvements in treating diabetic foot ulcers. Further studies are needed to assess the stages in which honey is most efficient in healing and where surgery may be necessary before use of honey. In addition, comparing honey that is raw versus honey that has been heat-treated as is the kind for consumer consumption

Interfaces Within Graphene Nanoribbons

We study the conductance through two types of graphene nanostructures: nanoribbon junctions in which the width changes from wide to narrow, and curved nanoribbons. In the wide-narrow structures, substantial reflection occurs from the wide-narrow interface, in contrast to the behavior of the much studied electron gas waveguides. In the curved nanoribbons, the conductance is very sensitive to details such as whether regions of a semiconducting armchair nanoribbon are included in the curved structure -- such regions strongly suppress the conductance. Surprisingly, this suppression is not due to the band gap of the semiconducting nanoribbon, but is linked to the valley degree of freedom. Though we study these effects in the simplest contexts, they can be expected to occur for more complicated structures, and we show results for rings as well. We conclude that experience from electron gas waveguides does not carry over to graphene nanostructures. The interior interfaces causing extra scattering result from the extra effective degrees of freedom of the graphene structure, namely the valley and sublattice pseudospins.Comment: 19 pages, published version, several references added, small changes to conclusion