Elastic tricriticality at the collapse of magnetic order in a valence fluctuating Eu-based compound.

Elastic tricriticality is observed at the collapse of magnetic order in EuPd2(Si1−xGex)2, where compressibility diverges universally with correlation length at a tricritical point.

• Why it matters: Spin and charge fluctuations are central to correlated-electron materials, yet their coupling to the crystal lattice is often treated as weak; this work tests whether it becomes nonperturbative at tricriticality.
• What they did: Single crystals of EuPd2(Si1−xGex)2 were studied as magnetic order collapses under strong valence fluctuations controlled by composition and pressure, using temperature and He-gas pressure length-change measurements to identify a TCP.
• The result: Elastic response measurements reveal signatures of elastic tricriticality, including a drastically enhanced compressibility, implying the tricritical universality class is modified by crystal elasticity.

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