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2026

Terahertz Imaging of Two-Dimensional High-Temperature Superconductor BSCCO | Nature

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The superconducting energy gap is the intrinsic energy scale that gives rise to dissipationless transport and collective effects in superconductors. In layered high-temperature cuprate superconductors, Cooper pairs are confined to the two-dimensional copper–oxygen CuO₂ planes, where coupling is relatively weak. Using sub-gap terahertz spectroscopy with energies on the order of a few millielectronvolts, key information about the collective superfluid response perpendicular to the superconducting layers has now been obtained. However, within the CuO₂ planes, the collective superfluid response manifests as plasma charge oscillations at energies far exceeding the superconducting energy gap, and this signal is masked by strong dissipative effects.

Recently, a team led by A. von Hoegen and N. Gedik at the Massachusetts Institute of Technology published a paper in Nature demonstrating, through spectroscopic experiments, the existence of two-dimensional superfluid plasmon modes below the energy gap in few-layer bismuth strontium calcium copper oxide (Bi?Sr?CaCu?O???), and resolving, on a spatial scale, the sub-diffraction-limit terahertz electrodynamic behavior.

When this superconductor is placed within the near field of a spintronic terahertz emitter, a distinctive resonant signal is observed—one that is absent in bulk samples and manifests only in the superconducting state. Furthermore, by mapping the geometric anisotropy and the dispersion relation, the plasmonic nature of this resonant signal is unequivocally confirmed. Crucially, these measurements provide a direct visualization of the superconducting transition process in a two-dimensional system, revealing its dependence on both momentum and frequency.

Imaging a terahertz superfluid plasmon in a two-dimensional superconductor. Imaging of terahertz superfluid plasmons in two-dimensional superconductors