Gaps and pseudo-gaps at the Mott quantum Critical point in the   perovskite rare earth nickelates
  We report on tunneling measurements that reveal for the first time the evolution of the quasi-particle state density across the bandwidth controlled Mott metal to insulator transition in the rare earth perovskite nickelates. In this, a canonical class of transition metal oxides, we study in particular two materials close to the T=0 metal-insulator transition: NdNiO3 , an antiferromagnetic insulator, and LaNiO3, a correlated metal. We measure a sharp gap in NdNiO3, which has an insulating ground state, of ~ 30 meV. Remarkably, metallic LaNiO3 exhibits a pseudogap of the same order that presages the metal insulator transition. The smallness of both the gap and pseudogap suggests they arise from a common origin: proximity to a quantum critical point at or near the T=0 metal-insulator transition. It also supports theoretical models of the quantum phase transition in terms of spin and charge instabilities of an itinerant Fermi surface. 
S. James Allen, Adam J. Hauser, Evgeny Mikheev, Jack Y. Zhang, Nelson   E. Moreno, Junwoo Son, Daniel G. Ouellette, James Ka...
cond-mat.str-el