A Hubbard exciton fluid in a photo-doped antiferromagnetic Mott insulator
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1.
California Institute of Technology
Abstract
The undoped antiferromagnetic Mott insulator naturally has one charge carrier per lattice site. When it is doped with additional carriers, they are unstable to spin-fluctuation-mediated Cooper pairing as well as other unconventional types of charge, spin and orbital current ordering. Photo-excitation can produce charge carriers in the form of empty (holons) and doubly occupied (doublons) sites that may also exhibit charge instabilities. There is evidence that antiferromagnetic correlations enhance attractive interactions between holons and doublons, which can then form bound pairs known as Hubbard excitons, and that these might self-organize into an insulating Hubbard exciton fluid. However, this out-of-equilibrium phenomenon has not been experimentally detected. Here we report the transient formation of a Hubbard exciton fluid in the antiferromagnetic Mott insulator Sr₂IrO₄ using ultrafast terahertz conductivity. Following photo-excitation, we observe rapid spectral-weight transfer from a Drude metallic response to an insulating response. The latter is characterized by a finite-energy peak originating from intraexcitonic transitions, whose assignment is corroborated by our numerical simulations of an extended Hubbard model. The lifetime of the peak is short (approximately one picosecond) and scales exponentially with the Mott gap size, implying extremely strong coupling to magnon modes.
Copyright and License
© The Author(s), under exclusive licence to Springer Nature Limited 2023.
Acknowledgement
We thank L. Balents, M. Ye, R. D. Averitt, P. A. Lee, M. Mitrano, M. Buzzi, S. K. Cushing, P. Prelovšek, D. Golež and V. Galitski for useful discussions. We thank S. J. Moon for sharing his equilibrium optical conductivity results. This work is supported by ARO MURI grant no. W911NF-16-1-0361. D.H. acknowledges support for instrumentation from the David and Lucile Packard Foundation and from the Institute for Quantum Information and Matter (IQIM), an NSF Physics Frontiers Center (PHY-1733907). S.D.W. acknowledges partial support via NSF award DMR-1729489. X.L. acknowledges support from the Caltech Postdoctoral Prize Fellowship and IQIM. M.B. acknowledges support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy Cluster of Excellence Matter and Light for Quantum Computing (ML4Q) EXC 2004/1-390534769. Z.L. was funded by the Gordon and Betty Moore Foundation's EPiQS initiative, grant no. GBMF4545, and J1-2463 project and P1-0044 program of the Slovenian Research Agency.
Contributions
These authors contributed equally: Omar Mehio, Xinwei Li, Honglie Ning.
O.M. and D.H. conceived the experiment. O.M. constructed the time-resolved time-domain THz spectrometer with contributions from X.L. and N.J.L. O.M., X.L., H.N. and Y.H. collected and analysed the data. Z.L. performed the exact diagonalization calculations and interpreted the results with O.M. and M.B. Z.P. and S.W. synthesized and characterized the sample. O.M. and D.H. wrote the paper with input from all authors.
Data Availability
Source data are provided with this paper. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
Conflict of Interest
The authors declare no competing interests.
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Additional details
- ISSN
- 1745-2481
- URL
- https://rdcu.be/dnPbi
- United States Army Research Office
- W911NF-16-1-0361
- David and Lucile Packard Foundation
- National Science Foundation
- PHY-1733907
- National Science Foundation
- DMR-1729489
- Deutsche Forschungsgemeinschaft
- (ML4Q) EXC 2004/1 390534769
- Gordon and Betty Moore Foundation
- GBMF4545
- Javna Agencija za Raziskovalno Dejavnost RS
- J1- 2463
- Javna Agencija za Raziskovalno Dejavnost RS
- P1-0044
- Accepted
-
2023-09-14published online
- Caltech groups
- Institute for Quantum Information and Matter