We report specific heat, resistivity and susceptibility measurements at different temperatures, magnetic fields, and pressures to provide solid evidence of CoS2 being a marginal Fermi liquid. The presence of a tricritical point in the phase diagram o
f the system provides an opportunity to test the spin fluctuation theory with a high limit of accuracy. A magnetic field suppresses the amplitude of the spin fluctuations and recovers conventional Fermi liquid behavior, connecting both states continuously.
We report high-pressure x-ray diffraction and magnetization measurements combined with ab-initio calculations to demonstrate that the high-pressure optical and transport transitions recently reported in TiOCl, correspond in fact to an enhanced Ti3+-T
i3+ dimerization existing already at room temperature. Our results confirm the formation of a metal-metal bond between Ti3+ ions along the b-axis of TiOCl, accompanied by a strong reduction of the electronic gap. The evolution of the dimerization with pressure suggests a crossover from the spin-Peierls to a conventional Peierls situation at high pressures.
Electronic structure calculations for spinel vanadate ZnV$_2$O$_4$ show that partial electronic delocalization in this system leads to structural instabilities. These are a consequence of the proximity to the itinerant-electron boundary, not being re
lated to orbital ordering. We discuss how this mechanism naturally couples charge and lattice degrees of freedom in magnetic insulators close to such a crossover. For the case of ZnV$_2$O$_4$, this leads to the formation of V-V dimers along the [011] and [101] directions that readily accounts for the intriguing magnetic structure of ZnV$_2$O$_4$.
We report a systematic enhancement of the pressure dependence of TN in A2+[V2]O4 spinels as the V-V separation approaches the critical separation for a transition to itinerant-electron behavior. An intermediate phase between localized and itinerant e
lectron behavior is identified in Zn[V2]O4 and Mg[V2]O4 exhibiting mobile holes as large polarons. In Zn[V2]O4, cooperative ordering of V-V pairs below a Ts=TN does not totally suppress the V3+-ion spins at ambient pressure, but makes TN to decrease with pressure. Our results demonstrate that Zn[V2]O4 and Mg[V2]O4 are less localized than previously thought.
Here we present experimental and computational evidences to support that rock-salt cubic VO is a strongly correlated metal with Non-Fermi-Liquid thermodynamics and an unusually strong spin-lattice coupling. An unexpected change of sign of metallic th
ermopower with composition is tentatively ascribed to the presence of a pseudogap in the density of states. These properties are discussed as signatures of the proximity to a magnetic quantum phase transition. The results are summarized in a new electronic phase diagram for the 3d monoxides, which resembles that of other strongly correlated systems. The structural and electronic simplicity of 3d monoxides make them ideal candidates to progress in the understanding of highly correlated electron systems.
