Hidden bulk phases revealed by Broken Symmetry at a Surface

Professor E. Ward Plummer
Department of Physics, Louisiana State University
Wednesday, February 27, 2019
4:00 pm
N2 1201
If you have taught or attended a condensed matter physics course, you know that the subjects are compartmentalized: lattice structure, electronic structure, lattice dynamics, magnetism and superconductivity.  The modern world of functional materials is not compartmentalized; it is the nonlinear entanglement of lattice, electron, and spin degrees of freedom that creates functionality, such as superconductivity, magnetoresistance, quantum criticality, etc.  Functional materials respond to external and internal stimuli, like temperature, pressure, field, or doping.  The goal of materials research is to learn to manipulate, control, or design the desired functionality.  One way to reveal new (hidden) phases in bulk is to explore the functionality of surfaces in an environment of broken symmetry.  Our group has investigated the surface properties of many complex materials, but in this talk I will describe antiphase spin domain walls  at the surface of the Fe based superconductor BaFe2As2,reconstructed surfaces of Ca(Fe1-xCox)2As, stabilizing Antiferromagnetic Ordering leading to the coexistence of superconductivity and antiferromagnetic ordering, and Mn doped double-layer RuthenateSr3(Ru1-xMnx)2O7, where the surface phase diagram is almost opposite from the bulk due to surface induced reconstruction.Our work show that creating a surface by breaking the translational symmetry is an effective way to reveal hidden phase’s non-existent in bulk.
Wilson Ho