Abstract
Excitonic Mott transition is a many-body crossover phenomenon where, even at zero temperature, a gas of excitons is expected to spontaneously ionize as its density or pressure is increased. Although this ionization due to the disappearance of the bound states from the energy spectra has long been predicted and continues to be studied, compelling demonstrations have been missing and the exact mechanism remains controversial. We revisit the phenomenon for silicon and report a number of striking features. The low temperature photoluminescence spectrum, around a certain crossover density shows a decrease in the emission intensity with increase in the excitation power. The photoluminescence efficiency (emission per incident photon) decreases by more than an order of magnitude building up to the Mott crossover, after which it becomes almost constant. This drastic loss in the oscillator strength is accompanied onset of a strong broadening of the excitonic peak. A comparison of this low temperature excitation power-dependent behavior of the photoluminescence emission with its temperature dependent change rules out the observations being explained by just the laser-induced heating of the sample.
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This manuscript has no associated data or the data will not be deposited. [Authors’ comment: The data that support the findings of this study are available on reasonable request from the corresponding author].
Notes
For a silicon sample mounted in the vacuum in a cold finger-based cryostat, temperatures below 20 K are sometimes unattainable due to differential heating of the sample with respect to the cold finger [38]. Unless the sample is immersed in liquid helium, the possibility of observing the electron-hole drops is eliminated [27, 29]. Many recent measurements on the Mott crossover have been deliberately performed at higher temperatures to avoid the electron-hole drop formation [23].
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Acknowledgements
Bhavtosh Bansal thanks the Science and Engineering Research Board, Department of Science and Technology, Government of India, for the Core Research Grant (No. CRG/2018/003282 and CRG/2022/008662). Basabendra Roy thanks Council of Scientific and Industrial Research (CSIR), India for financial support.
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BB conceived of the study and guided the research work. The experiments were done by BR. Both authors discussed the results and wrote the manuscript.
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Roy, B., Bansal, B. Exciton-to-plasma Mott crossover in silicon. Eur. Phys. J. D 78, 24 (2024). https://doi.org/10.1140/epjd/s10053-024-00814-w
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DOI: https://doi.org/10.1140/epjd/s10053-024-00814-w