Reinforce the collaboration on high temperature superconducting oxychlorides as a light element model for cuprates

• High temperature superconducting oxychlorides: a light element model for cuprates

  In the context of High Temperature Superconducting (HTS) cuprates HTS, the discovery of the Na and vacancy doped Ca₂CuO₂Cl₂ oxychloride mixed anions compounds, such as Ca_2-xCuO₂Cl₂ (vacancy doped CCOC) and Ca_2-xNa_xCuO₂Cl₂ (or Na-CCOC), is very promising indeed to bridge the gap between theory and experiment since these compounds:
  • lack high Z ions;
  • have a simple I4/mmm 1-layer structure, typical of "214" (LSCO) cuprates, but which is stable at all doping and temperatures;
  • and have a strong 2D character due to the replacements of apical oxygen with chlorine.
  Moreover, the superconducting dome seems very simple, without any plateau around 1/8 hole doping as for most other systems [Hirai2007]. Theoretical studies in these compounds, in particular numerical approaches, take advantage from their simplicity, as they are composed of only low Z ions, reducing the number of electrons involved, and their very simple crystalline structure without phase transition. This is already the case for standard ab-initio calculations based on DFT, where large Z ions pose problems for the pseudo-potential optimisation. It is even more the case for advanced methods trying to catch the correlations effect as e.g. Quantum Monte Carlo (QMC) and Dynamical Mean Field Theory (DMFT) calculations, where the strong spin-orbit coupling is highly challenging to treat accurately, and the reduced number of electrons drastically reduces the CPU cost needed. The insight gained by comparing such calculations with our experimental results will help understanding high temperature superconducting cuprates as a whole.
  
  However, to handle these compounds is quite difficult, as they are highly hygroscopic, and available only in small volume size, which explain the lack of results on bulk properties as magnon dispersion, charge-density-wave properties, a recently renewed topic in cuprate phisics, and their interaction with phonons.
  
  In this context I developed protocols to handle oxychlorides sample in an appropriate way for hard-x-ray and soft x-ray experiment, and I took advantage to recent development of synchrotron-radiation based experiment to measure these properties in undoped CCOC and Na and vacancy doped ones.
  I am currently running a research program to extend these experiments in order to measure:
  1. the comparison of the experimental electronic structure with state-of-the-art cluster-DMFT calculations,
  2. their magnetic field penetration length λ;
  3. the bulk signature of charge-density-wave, and their interaction with charge carriers and Cooper pairs and phonons;
  4. the (para-)magnon dispersion and its spectral weight as a function of doping

  High temperature superconductivity in cuprate: mechanism and origin