Exploration of Hg-based cuprate superconductors by Raman spectroscopy under hydrostatic pressure
Résumé
The superconducting phase of the HgBa2CuO4+δ (Hg-1201) and HgBa2Ca2Cu3O8+δ (Hg-1223) cuprates has been investigated by Raman spectroscopy under hydrostatic pressure. Our analysis reveals that the increase of Tcwith pressure is slower in the Hg-1223 cuprate compared to Hg-1201 due to a charge carrier concentration imbalance accentuated by pressure in Hg-1223. We find that the energy variation under pressure of the apical oxygen mode from which the charge carriers are transferred to the CuO2 layer, is the same for both the Hg-1223 and Hg-1223 cuprates and it is controlled by the interlayer compressibility. At last, we show that the binding energy of the Cooper pairs related to the maximum amplitude of the d-wave superconducting gap at the antinodes does not follow Tcwith pressure. It decreases while Tcincreases. In the particular case of Hg-1201, the binding energy collapses from 10 to 2 KBTc as the pressure increases up to 10 GPa. These direct spectroscopic observations joined to the fact that the binding energy of the Cooper pairs at the antinodes does not follow Tceither with doping, raises the question of its link with the pseudogap energy scale which follows the same trend with doping.
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