Correlation effects and spin dependent transport in carbon nanostructures

The impact of symmetry breaking perturbations on the spin dependent transport through carbon nanotube quantum dots in the Kondo regime is discussed.Comment: 10 pages, 6 figure

Investment Decision in a Broadband Internet Network: A Real Options Approach

This article is a case study analysing the decision of a telecommunications operator to roll out ADSL infrastructures in areas of low population density. This type of investment is characterized by the risk of committing significant sunk costs for a low number of potential subscribers. In addition, the investment decision is complicated by the involvement of local authorities which are interested in offering broadband internet access to the local population, and are prepared to partially fund the project. Real options are used to calculate the project's value and optimal timing of the investment. Particular attention is paid to provide detail on how to perform real options analysis and valuation. The option is evaluated with the binomial model and we explain how to estimate key parameters such as volatility. The case study suggests that real options can produce a more sensible recommendation regarding investment timing than the net present value (NPV) rule. It also illustrates the benefits of real options beyond mere valuation aspects. In particular, this approach can help structure discussions with local authorities and enables the operator to establish a roll-out plan of ADSL infrastructures across the entire network.Investment under Uncertainty; real options; telecommunications networks; case study.

Spin dependent conductance of a quantum dot side attached to topological superconductors as a probe of Majorana fermion states

Spin-polarized transport through a quantum dot side attached to a topological superconductor and coupled to a pair of normal leads is discussed in Coulomb and Kondo regimes. For discussion of Coulomb range equation of motion method with extended Hubbard I approximation is used and Kondo regime is analyzed by Kotliar-Ruckenstein slave boson approach. Apart from the occurrence of zero bias anomaly the presence of Majorana states reflects also in splitting of Coulomb lines. In the region of Coulomb borders the spin dependent negative differential conductance is observed. Due to the low energy scale of Kondo effect this probe allows for detection of Majorana states even for extremely weak coupling with topological wire. In this range no signatures of Majorana states appear in Coulomb blockade dominated transport.Comment: 3 pages, 3 figure