Title: The Challenge of Spin-Orbit-Tuned Ground States in Iridates,
Abstract: Effects of spin-orbit interactions in condensed matter are an important and
rapidly evolving topic. Strong competition between spin-orbit, on-site Coulomb
and crystalline electric field interactions in iridates drives exotic quantum
states that are unique to this group of materials. In particular, the Jeff =
1/2 Mott state served as an early signal that the combined effect of strong
spin-orbit and Coulomb interactions in iridates has unique, intriguing
consequences. In this Key Issues Review, we survey some current experimental
studies of iridates. In essence, these materials tend to defy conventional
wisdom: absence of conventional correlations between magnetic and insulating
states, avoidance of metallization at high pressures, S-shaped I-V
characteristic, emergence of an odd-parity hidden order, etc. It is
particularly intriguing that there exist conspicuous discrepancies between
current experimental results and theoretical proposals that address
superconducting, topological and quantum spin liquid phases. This class of
materials, in which the lattice degrees of freedom play a critical role seldom
seen in other materials, evidently presents some profound intellectual
challenges that call for more investigations both experimentally and
theoretically. Physical properties unique to these materials may help unlock a
world of possibilities for functional materials and devices. We emphasize that,
given the rapidly developing nature of this field, this Key Issues Review is by
no means an exhaustive report of the current state of experimental studies of
iridates.