Shining a light on High Tc Superconductivity in the Iron Age

Peter D. Johnson
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York

Photoemission has developed into a powerful probe of condensed matter.  Modern technical developments enable the study of not only the single particle spectra but also the interaction with collective excitations.  In this talk we present an overview of the modern photoemission experiment with demonstrations of its application to the high Tc superconductors.  In particular we focus on studies of the more recently discovered Fe-based superconductors using not only synchrotron radiation but also lasers as the photon source; the latter allowing very high energy and momentum resolution of the electronic structure.  A recent and powerful development in condensed matter physics has been the realization of the role of topology.  The two fields, topology and superconductivity, have collided in the Fe based superconductors with the recent identification of topological states at the center of the zone in the Fe-chalcogenide family, FeTe1-xSex.  Laser based photoemission studies of the topological states appear to indicate time reversal symmetry breaking at the superconducting transition.  We discuss these observations and what they may imply for surface superconductivity and the superconducting order parameter in the Fe-based superconductors.

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Dr. Johnson is an internationally recognized leader in surface science and photoelectron spectroscopy, a process in which an electron absorbs energy from light and is ejected from the material under study, thus revealing information about its properties. Johnson has focused on materials in which electrons are confined to two dimensions, rather than the usual three dimensions. Two-dimensional materials include the surfaces of metals, where catalytic reactions take place; magnetic multilayers, consisting of alternating layers of thin films of magnetic and nonmagnetic materials; and high-temperature superconductors.

A recipient of the American Physical Society's Oliver E. Buckley Prize in 2011 and Brookhaven Lab's Science and Technology Award in 2001, Dr. Johnson is a Fellow of the American Association for the Advancement of Science, the American Physical Society and the Institute of Physics in the United Kingdom.