講 師： Prof. Yasutomo Uemura (Columbia University)
題 目：First-order quantum evolution with phase separation in Mott transition systems (RENiO3, V2O3), unconventional superconductors, and itinerant-electron magnets
RENiO3 (RE = Rare Earth) and V2O3 are prototypical systems which exhibit Mott metal-insulator transition and associated antiferromagnetic (AF) order. The AF insulator state can be driven to paramagnetic metal state in quantum tuning by RE element substitutions in RENiO3 and application of hydrostatic pressure in V2O3. We have performed muon spin relaxation measurements in these systems and found that the magnetically ordered state disappears in quantum tuning associated with decreasing volume fraction in phase separation without change of the local ordered moment size. Similar behavior in disappearance of magnetic order was also found in unconventional superconductors Ba(Fe,Ni)2As2, overdoped Na(Fe,Cu)As, and itinerant electron magnets MnSi, Sc3In and (Sr,Ca)RuO3. To our surprise, pressure tuning of (Mn,Fe)Si exhibits tendency towards restoration of second order quantum criticality due to dosorder. We discuss implications of these results on unconventional superconductors, and relevance to the theory of itinerant-electron magnets by Belitz and Kirkpatrick.