Sharp tunnelling resonance from the vibrations of an electronic Wigner crystal

Abstract

Photoemission and tunnelling spectroscopies measure the energies at which single electrons can be added to or removed from an electronic system1. Features observed in such spectra have revealed electrons coupling to vibrational modes of ions both in solids2 and in individual molecules3. Here we report the discovery of a sharp resonance in the tunnelling spectrum of a two-dimensional electron system. Its behaviour suggests that it originates from vibrational modes, not involving ionic motion, but instead arising from vibrations of spatial ordering of the electrons themselves. In a two-dimensional electronic system at very low temperatures and high magnetic fields, electrons can either condense into a variety of quantum Hall phases or arrange themselves into a highly ordered ‘Wigner’ crystal lattice4,5,6. Such spatially ordered phases of electrons are often electrically insulating and delicate, and have proven very challenging to probe with conventional methods. Using a pulsed tunnelling method capable of probing electron tunnelling into insulating phases, we observe a sharp peak with dependencies on energy and other parameters that fit to models for vibrations of a Wigner crystal7,8. The remarkable sharpness of the structure presents strong evidence of the existence of a Wigner crystal with long correlation length.

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Figure 1: Pulsed tunnelling measurement set-up and TDOS of 2D holes.
Figure 2: Dependence on ν of the resonance energy εr at various magnetic fields.
Figure 3: Temperature dependence of the magnetophonon resonance.
Figure 4: Control of the tunnelling resonances of 2D electrons.

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Acknowledgements

The work at MIT was funded by the BES Program of the Office of Science of the US DOE, contract no. FG02-08ER46514, and the Gordon and Betty Moore Foundation, through grant GBMF2931. The work at Princeton University was funded by the Gordon and Betty Moore Foundation through the EPiQS initiative Grant GBMF4420, and by the National Science Foundation MRSEC Grant DMR-1420541. We thank P. A. Lee and I. Sodemann for helpful conversations. We thank N. Staley for a careful proofreading of the manuscript and A. Demir for assistance in amplifier design.

Author information

J.J. and B.M.H. performed measurements. J.J. and R.C.A. analysed data. K.W.W. and L.N.P. grew GaAs/AlGaAs heterostructures. All authors discussed the results. J.J. and R.C.A. wrote the paper, and R.C.A. supervised the overall project.

Correspondence to Joonho Jang or Raymond C. Ashoori.

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Jang, J., Hunt, B., Pfeiffer, L. et al. Sharp tunnelling resonance from the vibrations of an electronic Wigner crystal. Nature Phys 13, 340–344 (2017). https://doi.org/10.1038/nphys3979

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