Surface Electronic States

Symmetry makes mathematics much more manageable, and much of the predictive power of condensed matter physics is possible because we assume matter has a unique symmetry – the infinite, periodic lattice.  Imagine a stack of graph paper with an atom at every intersection of the lines on the sheets.  An infinite stack of sheets of infinite size would make an infinite lattice.  If you got rid of half the stack it would create a surface.  It would still extend infinitely long, wide and deep, but there would be nothing above it.  We call this idea breaking symmetry, and some cool things happen when the symmetry of the lattice is broken at a surface.  It invalidates the assumption of infinite extension in one direction, but physics can’t just stop there because of the need for continuity.  Amazingly, theory predicts that electrons can exist here as a direct result of the broken symmetry.  We call these surface electronic states and resonances, and I’m primarily interested in investigating unoccupied ones with IPES.