Thesis presented May 26, 2008

Abstract:
We investigate in extreme conditions of high pressure and low temperature the phase diagram (p,T) for ytterbium-based strongly correlated electron compounds, and also the superconducting phase which appears under pressure in the spin-ladder compound Na_0,33V₂O₅. Particular emphasis is made on high quality crystals and good hydrostatic conditions.
To achieve this, we developed a new technique to measure resistivity under pressure up to 8 GPa to millimetric samples.
We showed that no magnetic phase exists under pressure up to about 6 GPa for YbAl₃, down to 2 K. Resistivity measurements on high quality YbCu₂Si₂ single crystals showed anisotropy. We performed measurements under pressure to investigate precisely the phase diagram in the vicinity of the magnetic phase appearance, around 8 GPa.
Resistivity measurements were performed on the spin ladder compound Na_0,33V₂O₅ to 7 GPa. We discuss about experimental reasons which prevent us to observe the superconducting phase.

Keywords:
Correlated electron systems, Quantum Critical Point, Intermediate valence ytterbium compounds, Unconventional superconductivity, Spinladder compounds, High hydrostatic pressures

On-line thesis.