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Uranium phase diagram fully understood


​This result is on the front page of Physical Review Letters. The article reports on an experimental study coupled to theoretical calculations explaining the phase diagram of uranium, for which the competition between superconductivity and charge density waves (CDW), tuned by pressure, is a major feature.

Published on 23 September 2011
Despite uranium uniqueness, such complete results pave the way for studies of strongly correlated electronic systems which exhibit a competition between ground states, sometimes surprising.

Figure: Fermi surface topology (section) of uranium calculated at ambient pressure (top) and 20GPa (bottom). The different colors correspond to the different sheets of the Fermi surface.

Phonon dispersion as a function of pressure was measured by inelastic X-Ray scattering at ESRF (ID287 beamline). The full agreement with the theory by Johann Bouchet from CEA/DAM enabled a more detailed study of electron-phonon coupling, which reveals as the key factor governing CDW stabilization below 1.5GPa. In contrast to the common explanation involving a variation in the nesting of the Fermi surface: there is almost no change from 0 to 20GPa (Figure) To end with, the pressure dependence of the superconducting critical temperature was modelled in excellent agreement with experiment.
This work has been done in collaboration between SPSMS, CEA/DAM, ESRF, UPMC and LANL (USA).

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