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

Nature Physics (2024)Cite this article

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Abstract

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.

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Fig. 1: Hall effect in Sr2−xLaxIrO4.
Fig. 2: Longitudinal resistivity and mobility of Sr2−xLaxIrO4.
Fig. 3: Low-temperature specific heat of Sr2−xLaxIrO4.
Fig. 4: Doping evolution of the Hall number and specific heat in the T = 0 limit.

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Data availability

Source data are provided with this paper and available from the Dryad data repository (https://doi.org/10.5061/dryad.79cnp5j4h)55. Any additional data are available from the corresponding authors upon request.

Code availability

The codes associated with the band structure and transport coefficient calculations that support this study are available from the corresponding authors upon request.

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Acknowledgements

We thank F. Baumberger, A. Georges and A. Tamai for fruitful discussions. We would like to thank R. D. H. Hinlopen for assistance with the numerical calculations and G. Stenning and D. Nye for help with the Physical Property Measurement System and Smartlab instruments in the Materials Characterisation Laboratory at the ISIS Neutron and Muon Source. We acknowledge the support of the High Field Magnet Laboratory (Grant No. HFML-RU/NWO-I), a member of the European Magnetic Field Laboratory. This work was supported by the European Research Council under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 835279-Catch-22), by the Swedish Research Council (Grant No. 2021-04360) and by the UK Engineering and Physical Sciences Research Council (Grant Nos. EP/N034694/1 and EP/V02986X/1). Part of this work was also supported by the former Foundation for Fundamental Research on Matter, which is financially supported by the Netherlands Organisation for Scientific Research (Grant No. 16METL01, ‘Strange Metals’).

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Authors and Affiliations

  1. High Field Magnet Laboratory (HFML-FELIX) and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands

    Yu-Te Hsu, Maarten Berben, Caitlin Duffy & Nigel E. Hussey

  2. Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

    Yu-Te Hsu

  3. Department of Physics, Stockholm University, Stockholm, Sweden

    Andreas Rydh

  4. Department of Physics, Northeastern University, Boston, MA, USA

    Alberto de la Torre

  5. London Centre for Nanotechnology and Dept. of Physics and Astronomy, University College London, London, UK

    Robin S. Perry

  6. ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Harwell, UK

    Robin S. Perry

  7. H. H. Wills Physics Laboratory, University of Bristol, Bristol, UK

    Nigel E. Hussey

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Contributions

Y.-T.H. designed the project. R.S.P. and A.d.l.T. grew and characterized the crystals. Y.-T.H., M.B. and C.D. performed the magnetotransport measurements. A.R. performed the specific heat measurements. Y.-T.H. performed the numerical calculations. Y.-T.H. and N.E.H. wrote the paper with inputs from all authors.

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Correspondence to Yu-Te Hsu or Nigel E. Hussey.

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Nature Physics thanks Danfeng Li and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–6, Discussion and Tables 1 and 2.

Source data

Source Data Fig. 1

Measured experimental data.

Source Data Fig. 2

Measured experimental data and calculated transport coefficients.

Source Data Fig. 3

Measured experimental data.

Source Data Fig. 4

Calculated transport and thermodynamic coefficients.

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Hsu, YT., Rydh, A., Berben, M. et al. Carrier density crossover and quasiparticle mass enhancement in a doped 5d Mott insulator. Nat. Phys. (2024). https://doi.org/10.1038/s41567-024-02564-3

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