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New techniques are advancing the frontier of high-pressure physics beyond 1 terapascal, leading to new discoveries and offering stringent tests for condensed-matter theory and advanced numerical methods. However, the ability to absolutely determine the pressure state remains challenging, and well-calibrated pressure-density reference materials are required. We conducted shockless dynamic compression experiments at the National Ignition Facility and the Z machine to obtain quasi-absolute, high-precision, pressure-density equation-of-state data for gold and platinum. We derived two experimentally constrained pressure standards to terapascal conditions. Establishing accurate experimental determinations of extreme pressure will facilitate better connections between experiments and theory, paving the way toward improving our understanding of material response to these extreme conditions.

We demonstrate from detailed ac susceptibility and calorimetry studies under hydrostatic pressure that YbCu2Si2 probably orders ferromagnetically at high pressure. The (p,H,T) phase diagram shows that the transition temperature increases with pressure but also with an applied magnetic field. We suggest that many ytterbium systems may show a trend towards ferromagnetism and we discuss the possible reasons for this. We also examine the implications, including the potential of YbCu2Si2 and other Yb compounds for further studies of the rich physical properties that may occur near a ferromagnetic critical point.