Existence of the Abrikosov vortex state in two-dimensional type-II superconductors without pinning

Theory alternative to the vortex lattice melting theories is advertised. The vortex lattice melting theories are science fiction cond-mat/9811051 because the Abrikosov state is not the vortex lattice with crystalline long-range order. Since the fluctuation correction to the Abrikosov solution is infinite in the thermodynamic limit (K.Maki and H.Takayama, 1972) any fluctuation theory of the mixed state should consider a superconductor with finite sizes. Such nonperturbative theory for the easiest case of two-dimensional superconductor in the lowest Landau level approximation is presented in this work. The thermodynamic averages of the spatial average order parameter and of the Abrikosov parameter $\beta_{a}$ are calculated. It is shown that the position H_{c4} of the transition into the Abrikosov state (i.e. in the mixed state with long-range phase coherence) depends strongly on sizes of two-dimensional superconductor. Fluctuations eliminate the Abrikosov vortex state in a wide region of the mixed state of thin films with real sizes and without pinning disorders, i.e. H_{c4} << H_{c2}. The latter has experimental corroboration in Phys.Rev.Lett. 75, 2586 (1995).Comment: 4 pages, 0 figure

Flux-lattice melting in two-dimensional disordered superconductors

The flux line lattice melting transition in two-dimensional pure and disordered superconductors is studied by a Monte Carlo simulation using the lowest Landau level approximation and quasi-periodic boundary condition on a plane. The position of the melting line was determined from the diffraction pattern of the superconducting order parameter. In the clean case we confirmed the results from earlier studies which show the existence of a quasi-long range ordered vortex lattice at low temperatures. Adding frozen disorder to the system the melting transition line is shifted to slightly lower fields. The correlations of the order parameter for translational long range order of the vortex positions seem to decay slightly faster than a power law (in agreement with the theory of Carpentier and Le Doussal) although a simple power law decay cannot be excluded. The corresponding positional glass correlation function decays as a power law establishing the existence of a quasi-long range ordered positional glass formed by the vortices. The correlation function characterizing a phase coherent vortex glass decays however exponentially ruling out the possible existence of a phase coherent vortex glass phase.Comment: 12 pages, 21 figures, final version to appear in Phys. Rev.

Carrier grade metro ethernet networks

This paper gives an overview on actual trends and deployments of carrier- grade Ethernet in metro, access, and core networks. This includes the related motivation, concepts, and technologies as well as open issues regarding research, development, and standardization. Ethernet as a packet-based, connection-oriented technology is deployed for metro networks worldwide today. This is driven by the massive increase of (IP- based) data traffic and the related applications. The Ethernet deployments aim at most cost-efficient data service provisioning and the migration of all legacy Layer-2 services towards a unified platform. The goal is a massive reduction of both, CapEx and OpEx. Network operators and service providers impose increased requirements regarding scalability, quality of service including reliability and availability, and Operations, Administration, and Maintenance (OAM) features on their metro Ethernet solutions. These requirements are usually referred to as carrier-grade or transport Ethernet. Metro Ethernet services as deployed today mainly consist of Ethernet Private Lines (EPL) or Ethernet Virtual Private LANs (EVPLAN). These can provide dedicated LAN extension or LAN- like connectivity via IP/MPLS, respectively. A different approach is Pseudowire Emulation Edge-to-Edge (PWE3) which allows MPLS transport of Ethernet and other packet services as well as synchronous TDM services. Various network architecture and protocol options exist to migrate from metro SONET/SDH and WDM networks towards even more Ethernet-centric and - optimized networks. These include Layer-2 transport like Transport MPLS (T-MPLS), Provider Backbone Transport (PBT), and Ethemet-over- SONET/SDH/WDM/OTH. These services are currently under investigation or being standardized, and they will also migrate into long-haul and backbone networks. These approaches have common requirements regarding network and control planes (e.g., ASON/GLMPS, GELS, T-MPLS). Thus, the corresponding management and control mechanisms have to have an integrated view on the lower 3 network layers. Further challenges for transport Ethernet result from upcoming technology steps like 100 Gbps Ethernet. Again, carrier-grade requirements and interworking aspects with transport networks have to be taken into account