The following commentary, written with my postdoc advisor Nuh Gedik, is available online:

This commentary is part of an upcoming issue of Nature Physics, focusing on quantum materials, and it discusses the contributions that the experimental technique of angle-resolved photoemission spectroscopy (ARPES) has made to this research area. Quantum materials exhibit a panoply of phenomena, and this diverse class of materials are linked together via a shared paradigm of emergence–the idea that the aggregate many-electron properties of materials cannot be derived from the behavior of a single electron (i.e. more is different). Trying to understand or predict these emergent phenomena drives basic research in this area, but in the future, the fruits of this research may have applications in materials for energy production/harnessing and next-generation electronics.

ARPES directly measures how electrons move in crystalline solids, and can thus pinpoint emergent electronic phenomena with high precision. The present commentary discusses how ARPES experiments have illuminated important physics in three classes of quantum materials (cuprate high temperature superconductors, iron-based high temperature superconductors, topological insulators), and how the challenges presented by these materials have in turn driven the improvement of ARPES experimental technology. One of these state-of-the-art ARPES instruments will be installed in my lab in the next several months!