PrOs₄Sb₁₂ is a filled skutterudite material, with unconventional superconductivity below 1.8 K [1] and magnetic-field-induced antiferroquadrupolar (AFQ) order in the region of 4.2 - 14 T, below 1 K [2,3]. In previous work [4], we showed that de Haas-van Alphen oscillations are strongly coupled to the AFQ order parameter in this system, and, on following the order parameter to very low temperatures, found that hyperfine states become involved in the AFQ order below 250 mK. This leads to a new phase in which nuclear and electronic degrees of freedom order simultaneously to create composite nuclear-electronic order. I will present the results of recent measurements that have allowed us to characterise this exotic order using quantum oscillations, and will show how it modifies both the low temperature phase transitions near the quantum critical points at the boundaries to the AFQ phase, and the quasiparticle effective masses. Nuclear-electronic interactions have been shown to strongly influence the properties of other important correlated electron systems at ultra-low temperatures [5], and our results indicate that the strong hyperfine coupling and relatively high temperature at which the nuclear-electronic order can be accessed in PrOs₄Sb₁₂ make it an ideal system in which to study the role of nuclear-electronic interactions in relation to multipole order, quantum criticality and superconductivity.


[1] E. Bauer et al., Physical Review B, 65, 100506(R) (2002).
[2] Y. Aoki et al., Journal of the Physical Society of Japan, 71, 2098 (2002).
[3] K. Kaneko et al., Physical Review B, 75, 094408 (2007).
[4] A. McCollam et al., Physical Review B, 88, 075102 (2013).
[5] E. Schuberth et al., Science, 352, 485 (2016).