Carrier density crossover and quasiparticle mass enhancement in a doped 5d Mott insulator

Yu-Te Hsu^1,2*, Andreas Rydh³, Maarten Berben², Caitlin Duffy², Alberto de la Torre⁴, Robin Perry⁵, Nigel Hussey^2,6

¹Department of Physics, National Tsing Hua Univeristy, Hsinchu City, Taiwan
²High Field Magnet Laboratory, Radboud University, Nijmegen, Netherlands
³Department of Physics, University of Stockholm, Stockholm, Sweden
⁴Department of Physics, Northeastern University, Boston, USA
⁵Department of Physics and Astronomy, University College London, London, UK
⁶H H Wills Physics Laboratory, University of Bristol, Bristol, UK

* Presenter:Yu-Te Hsu, email:ythsu@phys.nthu.edu.tw

High-temperature superconductivity in cuprates emerges upon doping the parent Mott insulator. Key features of the low-doped cuprate superconductors include an effective carrier density that tracks the number of doped holes, the emergence of an anisotropic pseudogap that is characterized by disconnected Fermi arcs and the closure of the gap at a critical doping level. In Sr2IrO4, a spin–orbit-coupled Mott insulator often regarded as a 5d analogue of the cuprates, surface probes have also revealed the emergence of an anisotropic pseudogap and Fermi arcs under electron doping. However, neither the corresponding critical doping nor the bulk signatures of pseudogap closure have yet been observed. Here we demonstrate that electron-doped Sr2IrO4 exhibits a critical doping level with a marked crossover in the effective carrier density at low temperatures. This is accompanied by a five-orders-of-magnitude increase in conductivity and a sixfold enhancement in the electronic specific heat. These collective findings resemble the bulk pseudogap phenomenology in cuprates. However, given that electron-doped Sr2IrO4 is non-superconducting, it suggests that the pseudogap may not be a state of precursor pairing. Therefore, our results narrow the search for the key ingredient underpinning the formation of the superconducting condensate in doped Mott insulators.

Keywords: Superconductivity, Pseudogap, Iridate