Abstract
Perovskite-type iridates SrIrO3 and CaIrO3 are a Dirac line node semimetal protected by crystalline symmetry, providing an interesting playground to investigate electron correlation effects on topological semimetals. The effect of Sn doping was examined by growing SrIr1−xSnxO3 and CaIr1−xSnxO3 thin films epitaxially on the SrTiO3(001) substrate using pulsed laser deposition. Upon Sn doping, the semimetallic ground state switches into an insulator. As temperature is lowered, the resistivity, ρ(T), of SrIr1−xSnxO3 above a critical doping level (xc ∼ 0.1) shows a well-defined transition from the semimetal to a weakly ferromagnetic insulator at T = Tc. In contrast, ρ(T) of CaIr1−xSnxO3 with increasing x shows a rapid increase in magnitude but does not show a clear signature of metal-insulator transition in the temperature dependence. We argue that the contrasted behavior of the two closely related iridates reflects the interplay between the effects of electron correlation and disorder enhanced by Sn doping.
Highlights
With this unique opportunity of controlling the electron correlations and disorder in mind, we synthesized epitaxial thin films of SrIr1−xSnxO3 and CaIr1−xSnxO3 and measured their resistivity to probe the effects of Sn doping
5d iridium oxides with perovskite-related structures have been explored extensively as a mine for exotic quantum phases, partly because of an interplay of strong spin-orbit interaction and electron correlation of the 5d electrons.1 The strong spin-orbit coupling of ∼0.4 eV for 5d electrons, which is larger than the typical crystal field splitting of ≲0.1 eV within t2g,2 splits the t2g bands with five d electrons into the upper half-filled Jeff = 1/2 band and lower completely filled Jeff = 3/2 bands
The black box indicates the GdFeO3type unit cell. (b) X-ray diffraction (XRD) 2θ-θ scans of SrIr0.8Sn0.2O3 and CaIr0.8Sn0.2O3 thin films. [(c) and (d)] XRD-Reciprocal space mapping (RSM) around the 103STO Bragg peak of SrIr0.8Sn0.2O3 and CaIrO3, indicating that the in-plane lattice constant is locked to the substrate
Summary
With this unique opportunity of controlling the electron correlations and disorder in mind, we synthesized epitaxial thin films of SrIr1−xSnxO3 and CaIr1−xSnxO3 and measured their resistivity to probe the effects of Sn doping. We discovered a sharp contrast in the transition behavior between the Sr and Ca iridium perovskites: the appearance of well-defined transition from the Dirac semimetal to a magnetic insulator as a function of temperature above a critical Sn concentration of xc ∼0.1 for SrIrO3 and the continuous increase in resistivity without a clear signature of the semimetal-insulator transition for CaIrO3, which we ascribe to the interplay of the electron correlation and the disorder effect.
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