Enhanced high-pressure superconductivity and local structure of the Ba8 Si46 clathrate

F. Morales (1) , M. Núñez-Regueiro (2) , Pierre Toulemonde (3) , D. Machon (4) , S. Le Floch (4) , V. Pischedda (4) , P. Lagarde (5) , A. Flank (5) , J. Itié (5) , A. San-Miguel (4)

1 Instituto de Investigaciones en Materiales (Mexico, Mexico)
2 NEEL - MagSup - Magnétisme et Supraconductivité
3 NEEL - MRS - Matériaux, Rayonnements, Structure
4 ILM - Institut Lumière Matière [Villeurbanne]
5 SSOLEIL - Synchrotron SOLEIL

The high-pressure superconducting properties and the local structure of the Ba8Si46 clathrate have been studied using electrical resistance and x-ray absorption spectroscopy measurements up to more than 20 GPa. At pressures above 10–13 GPa, corresponding to a well-known volume collapse phase transformation, a sudden increase in the critical temperature leads to a maximum value of the superconducting critical temperature Tc of ∼8.5–9 K at 20 GPa. In the low-pressure clathrate phase, the superconducting critical temperature decreases as pressure is applied with an electron-phonon coupling constant λ=1.1 derived from the temperature evolution of the electrical resistance at different pressures. A progressive disorder in the Ba-Si correlations in the Ba@Si24 cages of the structure is observed for pressures beyond ∼5 GPa. These observations exclude a structural homothecy at the volume collapse transition. The high-pressure collapsed phase of Ba8Si46 is then associated with local structural changes and shows enhanced superconducting properties.

Domaines: Supraconductivité [cond-mat.supr-con]

F. Morales, M. Núñez-Regueiro, Pierre Toulemonde, D. Machon, S. Le Floch, et al.. Enhanced high-pressure superconductivity and local structure of the Ba8 Si46 clathrate. Physical Review B, 2016, 94 (10), pp.104507. ⟨10.1103/PhysRevB.94.104507⟩. ⟨hal-01692100⟩