19 research outputs found
Quantum wire networks with local Z2 symmetry
For a large class of networks made of connected loops, in the presence of an
external magnetic field of half flux quantum per loop, we show the existence of
a large local symmetry group, generated by simultaneous flips of the electronic
current in all the loops adjacent to a given node. Using an ultra-localized
single particle basis adapted to this local Z_2 symmetry, we show that it is
preserved by a large class of interaction potentials. As a main physical
consequence, the only allowed tunneling processes in such networks are induced
by electron-electron interactions and involve a simultaneous hop of two
electrons. Using a mean-field picture and then a more systematic
renormalization-group treatment, we show that these pair hopping processes do
not generate a superconducting instability, but they destroy the Luttinger
liquid behavior in the links, giving rise at low energy to a strongly
correlated spin-density-wave state.Comment: 16 pages, 9 figures, v.2 section IV D added,accepted for publication
in PR
A knitting algorithm for calculating Green functions in quantum systems
We propose a fast and versatile algorithm to calculate local and transport
properties such as conductance, shot noise, local density of state or local
currents in mesoscopic quantum systems. Within the non equilibrium Green
function formalism, we generalize the recursive Green function technique to
tackle multiterminal devices with arbitrary geometries. We apply our method to
analyze two recent experiments: an electronic Mach-Zehnder interferometer in a
2D gas and a Hall bar made of graphene nanoribbons in quantum Hall regime. In
the latter case, we find that the Landau edge state pinned to the Dirac point
gets diluted upon increasing carrier density.Comment: 7 pages, 5 figures, version for PR
Regular networks of Luttinger liquids
We consider arrays of Luttinger liquids, where each node is described by a
unitary scattering matrix. In the limit of small electron-electron interaction,
we study the evolution of these scattering matrices as the high-energy single
particle states are gradually integrated out. Interestingly, we obtain the same
renormalization group equations as those derived by Lal, Rao, and Sen, for a
system composed of a single node coupled to several semi-infinite 1D wires. The
main difference between the single node geometry and a regular lattice is that
in the latter case, the single particle spectrum is organized into periodic
energy bands, so that the renormalization procedure has to stop when the last
totally occupied band has been eliminated. We therefore predict a strongly
renormalized Luttinger liquid behavior for generic filling factors, which
should exhibit power-law suppression of the conductivity at low temperatures
E_{F}/(k_{F}a) >
1. Some fully insulating ground-states are expected only for a discrete set of
integer filling factors for the electronic system. A detailed discussion of the
scattering matrix flow and its implication for the low energy band structure is
given on the example of a square lattice.Comment: 16 pages, 7 figure
State Of the Art Report in the fields of numerical analysis and scientific computing. Final version as of 16/02/2020 deliverable D4.1 of the HORIZON 2020 project EURAD.: European Joint Programme on Radioactive Waste Management
Document information Project Acronym EURAD Project Title European Joint Programme on Radioactive Waste Management Project Type European Joint Programme (EJP) EC grant agreement No. 847593 Project starting / end date 1 st June 2019-30 May 2024 Work Package No. 4 Work Package Title Development and Improvement Of NUmerical methods and Tools for modelling coupled processes Work Package Acronym DONUT Deliverable No. 4.
"Drawing with a crack in concrete": A hybrid test to control mixed-mode crack propagation
International audienceno abstrac
Innovative tests for characterizing mixed-mode concrete fracture
International audienceno abstrac
: article lié au prix de thèse discerné au congrès TINCE 2016
article lié au prix de thèse discerné au congrès TINCE 2016International audienceThe knowledge of the concrete behavior is essential when analyzing the aging and leakage phenomena of production facilities. On the industrial level the concrete fracture characterization is currently performed through standard experimental tests that are not sufficiently rich to determine in an optimized manner all the corresponding characteristics. First there is a general lack of mixed mode loading experiments that produce non trivial crack paths. Moreover, even for some well defined material properties (as for example critical shear stress) the corresponding loading tests are not sufficiently developed, as the results are too dependent on aggregate distribution and specimen sizes. It means that we are still not able to locally reproduce some specific me-chanical stresses distribution and repeatedly check it in order to attain necessary accuracy. Therefore an improvement in corresponding measurement technique is still needed.When studying concrete fracture behavior the main difficulty is related to instable crack propagation. In the past some relevant works in mixed mode fracture were conducted by Nooru-Mohamed. More recently the work was extended employing an up-to-date full-field measurement technique.In this work, we develop a stable crack path control technique that allows “customized” cracking tests creation for the characterization of various materials. Using this technique well instrumented and discriminating mixed–mode crack propagation tests performed on VERCORS concrete samples are presented. Finally we discuss the relevance of these tests for various pa-rameters identification and some possible extension of stable crack path control technique
Comparison between experimental and numerical results of mixed-mode crack propagation in concrete: Influence of boundary conditions choice
International audienceno abstrac
A complex mixed-mode crack propagation test performed with a 6-axis testing machine and full-field measurements propagation
International audienceA new type of mixed mode crack propagation test is proposed. A single crack is initiated and propagates in a stable way up to complete failure. A combination of tensile, shear and in-plane rotation performed by a 6-axis testing machine is prescribed. The rotation creates a tension/compression gradient in the sample ensuring the stability, while the shear direction is closely related to the orientation of the crack and the tensile load is responsible for the actual propagation. The experiment is performed in an interactive manner, namely, depending on the crack tip position estimated by Digital Image Correlation (DIC) during the test, the loading is changed to bifurcate the crack. The displacements of the sample surfaces are assessed using multiple DIC measurements and displacement sensors. The displacement fields on each face of the sample give access to the crack pattern, and also to the actual boundary conditions that are crucial for a faithful numerical analysis of the test. Last, the 6 load components are recorded enabling for a complete description of the 3D mechanical behavior of the specimen