Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

Frandsen, B. A.*; Liu, L.*; Cheung, S. C.*; Guguchia, Z.*; Khasanov, R.*; Morenzoni, E.*; Munsie, T. J. S.*; Hallas, A. M.*; Wilson, M. N.*; Cai, Y.*; Luke, G. M.*; Chen, B.*; Li, W.*; Jin, C.*; Ding, C.*; Guo, S.*; Ning, F.*; Ito, Takashi   ; Higemoto, Wataru  ; Billinge, S. J. L.*; Sakamoto, Shoya*; Fujimori, Atsushi*; Murakami, Taito*; Kageyama, Hiroshi*; Antonio Alonso, J.*; Kotliar, G.*; Imada, Masatoshi*; Uemura, Yasutomo*

RENiO (RE = rare-earth element) and VO are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO) or pressure (VO), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation experiments that the QPT in RENiO and VO is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.