Transient superconductivity from electronic squeezing of optically pumped phonons

Abstract

Advances in light sources and time-resolved spectroscopy have made it possible to excite specific atomic vibrations in solids and to observe the resulting changes in electronic properties, but the mechanism by which phonon excitation causes qualitative changes in electronic properties has remained unclear. Here we show that the dominant symmetry-allowed coupling between electron density and dipole active modes implies an electron-density-dependent squeezing of the phonon state that provides an attractive contribution to the electron–electron interaction, independent of the sign of the bare electron–phonon coupling and with a magnitude proportional to the degree of laser-induced phonon excitation. Reasonable excitation amplitudes lead to non-negligible attractive interactions that may cause significant transient changes in electronic properties, including superconductivity. The mechanism is generically applicable to a wide range of systems, offering a promising route to manipulating and controlling electronic phase behaviour in novel materials.

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Figure 1: Schematic phase diagram of effective model, equation (3), in the plane of bare interaction U and pump fluence F (equivalently, mean boson occupancy nB), assuming a half-filled band.
Figure 2: Pump-induced time dependence of model parameters and gap functions.
Figure 3: Real and imaginary parts of non-equilibrium optical conductivity.

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Acknowledgements

A.J.M. and E.Y.W. were supported by the Basic Energy Sciences Program of the US Department of Energy under grant SC-0012592. D.M.K. was supported by DFG KE 2115/1-1. D.R.R. was supported by NSF CHE-1464802.

Author information

All authors contributed to planning the research, developing the methods interpreting the results, and writing the paper. E.Y.W. and D.M.K. performed the numerical calculations.

Correspondence to Andrew J. Millis.

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Kennes, D., Wilner, E., Reichman, D. et al. Transient superconductivity from electronic squeezing of optically pumped phonons. Nature Phys 13, 479–483 (2017). https://doi.org/10.1038/nphys4024

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