JCJC SIMI 4 - JCJC - SIMI 4 - Physique des milieux condensés et dilués

Superconductivity at the edge of a symmetric breaking – SUBRISSYME

Submission summary


In many strongly correlated electron systems, from heavy fermions to pnictides including high temperature superconductors, superconductivity seems to be linked to the vicinity of an electronic or magnetic instability. Despite the wide variety of systems, the generic phase diagram looks similar: a superconducting dome develops at low temperature, surrounding an electronic or a magnetic instability transition line. Furthermore, the superconductivity appears to be invariably enhanced when the symmetry breaking temperature transition tends to zero. A growing number of studies suggest that the presence of a hidden quantum critical point, i.e. a zero temperature transition, could explain the generic phase diagram and propose a superconductivity mechanism distinct from the conventional electron-phonon coupling. In this proposal we consider systems with charge order instability where magnetism is irrelevant. By combined experimental and theoretical approaches we aim to determine the microscopic ingredients involved in the formation of charge density waves and superconductivity and to unveil the general influence of the quantum critical point on the physical properties of those systems. Experimentally we will focus on the dichalcogenide family, and more particularly on doped 1T-TiSe2 at first. We plan to identify the relevant excitations of charge-density wave and superconductivity by spectroscopic techniques (ARPES, IXS, Point Contact Spectroscopy and Optical Spectroscopy) and by their theoretical counterparts (analytical and numerical investigations on model Hamiltonians). ARPES and IXS will be performed on synchrotron facilities. A cryogenic Point-Contact Spectroscopy setup will be built. An ambitious point of this project is the development of a laboratory optical spectroscopy set-up working down to low energy (down to 0.2 meV) and low temperature (down to 2 K) with a high energy resolution (5 µeV). Within the condensed matter community such set-up will be completely new throughout the French territory and will join the very restricted club of three others similar set-ups in the world. On the theory side the concept of quantum criticality will be applied to the understanding of the phase diagrams and the physical properties of the experimental systems studied in this proposal. This goal will be pursued by applying analytical and cutting-edge numerical techniques to model Hamiltonians that will mimic the collective behavior of the many-body excitations close to charge order transitions. This project is led by young physicists with complementary theoretical and experimental background fit to address the problem of quantum criticality and superconductivity close to charge ordering phase transitions.

Project coordination

Florence Levy-Bertrand (Institut Néel (CNRS)) – florence.levy-bertrand@neel.cnrs.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Institut Néel (CNRS)

Help of the ANR 289,347 euros
Beginning and duration of the scientific project: September 2012 - 36 Months

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