Approaching the quantum critical point in a highly correlated all-in–all-out antiferromagnet

Abstract

All-in--all-out (AIAO) antiferromagnets demonstrate vividly the effects of correlated charge and spin with strong spin-orbit coupling. Here, using resonant magnetic x-ray diffraction, the authors directly track the evolution of AIAO order in the pyrochlore Sm${}_{2}$Ir${}_{2}$O${}_{7}$ across a pressure-tuned quantum critical point. The results demonstrate a powerful approach to the quantum critical state driven by electron correlations $U$/$t$ and spin orbit coupling $\ensuremath{\lambda}$/$t$. The authors find prominent Ising-type spin fluctuations under pressure instead of the Heisenberg-type seen via chemical doping. This work also circumscribes the region of interest for the putative magnetic Weyl semimetal state in Pressure-Temperature space.