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Mott transition by an impulsive dielectric breakdown

Abstract

The transition of a Mott insulator to metal, the Mott transition, can occur via carrier doping by elemental substitution1, and by photoirradiation, as observed in transition-metal compounds2,3,4 and in organic materials5. Here, we show that the application of a strong electric field can induce a Mott transition by a new pathway, namely through impulsive dielectric breakdown. Irradiation of a terahertz electric-field pulse on an ET-based compound, κ-(ET)2Cu[N(CN)2]Br (ET:bis(ethylenedithio)tetrathiafulvalene)6, collapses the original Mott gap of 30 meV with a 0.1 ps time constant after doublon–holon pair productions by quantum tunnelling processes, as indicated by the nonlinear increase of Drude-like low-energy spectral weights. Additionally, we demonstrate metallization using this method is faster than that by a femtosecond laser-pulse irradiation and that the transition dynamics are more electronic and coherent. Thus, strong terahertz-pulse irradiation is an effective approach to achieve a purely electronic Mott transition, enhancing the understanding of its quantum nature.

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Figure 1: Fundamental properties in a bulk crystal and a strained thin crystal on a diamond substrate of κ-(ET)2Cu[N(CN)2]Br (κ-Br).
Figure 2: Absorption changes induced by a terahertz pulse and a near-IR light pulse.
Figure 3: Impulsive dielectric breakdown and Mott transition as a function of terahertz electric fields.
Figure 4: Time evolutions of absorption changes ΔOD and their analyses.

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Acknowledgements

We thank R. Shimano, N. Takubo and M. Takenaka for their collaborations in the early stage of this study. This work was partly supported by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS) (Project Numbers 25247049, 25247058, 25220709, and 15H03549), Nanotechnology Platform Program (Molecule and Material Synthesis) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and CREST, Japan Science and Technology Agency (Grant No. JPMJCR1661). H.Yamakawa, T.Morimoto and T.T. were supported by the JSPS through the Program for Leading Graduate Schools (MERIT).

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K.M. and K.K. provided single crystals. M.S., H.M.Y. and R.K. prepared thin single-crystalline samples on diamond substrates. H.Yamakawa measured the steady-state reflectance and transmittance spectra. H.Yamakawa, T.Miyamoto, T.Morimoto, T.T., H.Yada and N.K. constructed the terahertz-pump optical-probe and near-IR-pump optical probe systems. H.Yamakawa and T.Miyamoto performed the measurements. H.O. coordinated the study. H.Yamakawa and H.O. wrote the paper with inputs from all authors.

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Correspondence to H. Okamoto.

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The authors declare no competing financial interests.

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Yamakawa, H., Miyamoto, T., Morimoto, T. et al. Mott transition by an impulsive dielectric breakdown. Nature Mater 16, 1100–1105 (2017). https://doi.org/10.1038/nmat4967

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