Hydrostaticity and hidden order: effects of experimental conditions on the temperature–pressure phase diagram of URu₂Si₂

Abstract

The pressure dependence of the hidden order phase transition of URu₂Si₂ is shown to depend sensitively upon the quality of hydrostatic pressure conditions during electrical resistivity measurements. Hysteresis in pressure is demonstrated for two choices of pressure medium: the commonly used mixture of 1:1 Fluorinert FC70/FC77 and pure FC75. In contrast, no hysteresis is observed when the pressure medium is a 1:1 mixture of n-pentane/isoamyl alcohol, as it remains hydrostatic over the entire studied pressure range. Possible ramifications for the interpretation of the temperature–pressure phase diagram of URu₂Si₂ are discussed.

Keywords:

• hidden order
• hydrostaticity
• Fluorinert
• electrical resistivity

Acknowledgements

The authors thank S.K. McCall and D.D. Jackson for helpful discussions. This research was supported by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Research Grant # DE-FG52-06NA26205.