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Published July 15, 2012 | Published
Journal Article Open

Observation of a metal-to-insulator transition with both Mott-Hubbard and Slater characteristics in Sr_2IrO_4 from time-resolved photocarrier dynamics

Abstract

We perform a time-resolved optical study of Sr_2IrO_4 to understand the influence of magnetic ordering on the low energy electronic structure of a strongly spin-orbit coupled J_(eff) = 1/2 Mott insulator. By studying the recovery dynamics of photoexcited carriers, we find that upon cooling through the Néel temperature T_N the system evolves continuously from a metal-like phase with fast (∼50 fs) and excitation density independent relaxation dynamics to a gapped phase characterized by slower (∼500 fs) excitation density-dependent bimolecular recombination dynamics, which is a hallmark of a Slater-type metal-to-insulator transition. However our data indicate that the high energy reflectivity associated with optical transitions into the unoccupied J_(eff) = 1/2 band undergoes the sharpest upturn at TN, which is consistent with a Mott-Hubbard type metal-to-insulator transition involving spectral weight transfer into an upper Hubbard band. These findings show Sr_2IrO_4 to be a unique system in which Slater- and Mott-Hubbard-type behaviors coexist and naturally explain the absence of anomalies at T_N in transport and thermodynamic measurements.

Additional Information

©2012 American Physical Society. Received 20 March 2012. Published 18 July 2012. We thank F. Wang, T. Senthil, A. Vishwanath, S. Kehrein, K. Michaeli, R. Flint, S. Drapcho, and Y. Wang for useful discussions. N.G. acknowledges support from Army Research Office Grant No. W911NF-11-1-0331. C.G. acknowledges support through National Science Foundation Grants No. DMR-0856234 and No. EPS-0814194.

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