Tuning Physics and Chemistry in the ThCr2Si2 Structure - Iron and Beyond

The ThCr2Si2-type structure family is home to a vast landscape of interesting and exotic properties, hosting a variety of electronic ground states including magnetic, superconducting, and strongly correlated electron phenomena. The most famous example is the iron-based superconductor family of materials, which can be tuned by pressure, chemical stubstitution and charge doping to achieve high superconducting transition temperatures in the backdrop of a rich interplay of magnetic, electronic and topological phases and boundaries. The nematic phase, wherein electronic degrees of freedom drive a reduction in crystal rotational symmetry, is a common motif across a number of high temperature superconductors, and its appearance along with magnetic and quantum critical behavior has remained a challenge to understand. In this talk I will focus on a survey of observations in materials systems related to the iron-based superconductivity family that provide testbeds for understanding key ingredients of iron superconductors. I will discuss the interplay of electronic nematic degrees of freedom with superconductivity in the (Ba,Sr)Ni2As2 series, an nickel-based system without magnetism or unconventional pairing. I will also discuss topology and charge-ordered phases in the BaAl4-type structure family, which hosts a nontrivial topological band structure together with symmetry-breaking ground states including charge density wave (CDW) and magnetic orders, and finally quantum critical scale invariance in a disordered transition metal-pnictide system devoid of superconductivity.