In-gap state and effect of light illumination in CuIr${}_2$S${}_4$ probed by photoemission spectroscopy

Abstract

We have studied disorder-induced in-gap states and effect of light illumination in the insulating phase of spinel-type CuIr${}_2$S${}_4$ using ultra-violet photoemission spectroscopy (UPS). The Ir${}^{3+}$/Ir${}^{4+}$ charge-ordered gap appears below the metal-insulator transition temperature. However, in the insulating phase, in-gap spectral features with $softgap$ are observed in UPS just below the Fermi level ($E_F$), corresponding to the variable range hopping transport observed in resistivity. The spectral weight at $E_F$ is not increased by light illumination, indicating that the Ir${}^{4+}$-Ir${}^{4+}$ dimer is very robust although the long-range octamer order would be destructed by the photo-excitation. Present results suggest that the Ir${}^{4+}$-Ir${}^{4+}$ bipolaronic hopping and disorder effects are responsible for the conductivity of CuIr${}_2$S${}_4$.

arXiv comment14 pages, 5 figures

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Cited by in corpus (7)

• Local orbital degeneracy lifting as a precursor to an orbital-selective Peierls transition
• Two-orbital degeneracy lifted state as a local precursor to a metal-insulator transition
• X-ray induced electronic structure change in CuIr${}_2$S${}_4$
• Resolving Length Scale Dependent Transient Disorder Through an Ultrafast Phase Transition
• First-order kinetics bottleneck during photoinduced ultrafast insulator-metal transition in 3D orbitally-driven Peierls insulator CuIr${}_2$S${}_4$
• Orbitally-driven insulator-metal transition in CuIr${}_2$S${}_4$: Temperature dependent transient reflectivity study
• Superconductivity on the verge of metal-insulator transition in Cu${}_{1-x}$Zn${}_x$Ir${}_2$S${}_4$ probed by $\mu$SR