ABSTRACT
Quantum phase transitions are driven by quantum fluctuations that alter the nature of the electronic quasiparticles, resulting in phenomena such as non-Fermi liquid behaviour. Oxide heterostructures offer fundamentally new ways of manipulating quantum criticality. Here, we report on non-Fermi liquid behaviour in thin SrTiO3 quantum wells that are embedded in insulating, antiferromagnetic SmTiO3, as a function of temperature, quantum well thickness and SmTiO3 layer thickness in superlattices. Such quantum wells contain very high sheet carrier densities on the order of one electron per pseudocubic planar unit cell. We show that the quantum well thickness is a tuning parameter for non-Fermi liquid behaviour. Increasing the thickness by a single atomic layer and coupling in superlattices recover the Fermi liquid behaviour. The critical exponents, the symmetry of the order parameter, the role of carrier densities and symmetry-lowering distortions are discussed, and the results are compared with those of quantum wells embedded in ferrimagnetic GdTiO3.
ABSTRACT
Asperities play a central role in the mechanical and electrical properties of contacting surfaces. Changes in trends of uniaxial compression of an asperity tip in contact with a polycrystalline substrate as a function of substrate geometry, compressive stress and applied voltage are investigated here by implementation of a coupled continuum and atomistic approach. Surprisingly, an unmodified Au polycrystalline substrate is found to be softer than one containing a void for conditions of high stress and an applied voltage of 0.2 V. This is explained in terms of the temperature distribution and weakening of Au as a function of temperature. The findings in this communication are important to the design of materials for electrical contacts because applied conditions may play a role in reversing relative hardness of the materials for conditions experienced during operation.
