Matias Nunez

Interface phase and tuning of polarization in metal-ferroelectric junctions: A theoretical study

Using first principles calculations, we have studied how the control of the interface structure in metal-ferroelectric junctions can be used to tune the polarization of the ferroelectric film. Using a Pt∕BaTiO3∕Pt as a prototypical system, we show that the polarization of the oxide can be tuned by the introduction of an interface layer of a different metal and that this interface effect varies with the thickness of the ferroelectric film. These results can be easily interpreted in terms of the local electronic structure of the interface and provide a phenomenological criterion for choosing the metal intralayer in order to obtain the desired polarization.

Experimental consequences of quantum critical points at high temperatures

We study the Cr_(1-x) Re_x phase diagram finding that its phase transition temperature towards an antiferromagnetic order T_N follows a quantum [(x_c-x)/x_c ]^{\psi} law, with {\psi}=1/2, from the quantum critical point (QCP) at x_c=0.25 up to T_N=600K. We compare this system to others in order to understand why this elemental material is affected by the QCP up to such unusually high temperatures. We determine a general criterion for the crossover, as function of an external parameter such as concentration, from the region controlled solely by thermal fluctuations to that where quantum effects become observable. The properties of materials with low coherence lengths will thus be altered far away from the QCP.