Scientific Calendar Event

The experimental accessibility of high density phases in condensed matter systems, thanks to the advances of high pressure techniques over the last years, has switched pressure from being a less common external perturbation probe into an increasingly versatile tool in materials research.  Here, I want to focus on some selected pressure-induced effects in crystalline systems, in particular on how the natural effect of promoting more symmetric structure upon compressing the lattice can be worked out into a tuning of local and extended lattice distortions arising from charge-lattice coupling.  This is the exemplary case of the spontaneous symmetry breaking occurring in Jahn-Teller and Peierls systems.  The physics of these correlated materials is quite complex and typically characterized by a delicate interplay among different interactions at the same energy scale.  Applying pressure, over even a relatively small range (0-40 GPa), causes these systems to reach new, and sometimes unconventional, states but it also enables to disentangle the effects of the different coupling mechanisms thus gaining a deeper knowledge of the  ambient conditions phases.  As an example of a Jahn-Teller system I present an extended experimental study of La-Ca manganites (La1-xCaxMnO3) under high pressure (range 0-30 GPa), with particular attention to the parent LaMnO3 compound and the LaMn1-xGaxO3 family.  Recent high pressure experiments (range 0-20 GPa) on several Vanadium oxides with special focusing to the case of VO2 (Peierls system) is also discussed.  We will see that, apart from the characterization of the new higher density phases, the high pressure studies provide key information on the physics of these systems at ambient pressure which stimulates their theoretical modeling.
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