Speaker: Alex Potts, PhD, Columbia Research Staff
Title: "Finite-momentum Cooper plasmons in superconducting terahertz microcavities"
Talk abstract: The phase mode of a superconductor's order parameter encodes fundamental information about pairing and dissipation, but is typically inaccessible at low frequencies due to the Anderson-Higgs mechanism. Superconducting samples thinner than the London penetration depth, however, support a gapless phase mode whose dispersion can be reshaped by a proximal screening layer. Here, we theoretically and experimentally show that this screened phase mode in a superconducting thin film integrated into on-chip terahertz circuitry naturally forms a superconducting microcavity that hosts resonant finite-momentum standing waves of supercurrent density, which we term Cooper plasmons. We measure two Cooper plasmons in a superconducting NbN microcavity and demonstrate that their resonance frequencies and linewidths independently report the density of participating carriers and plasmon's dissipation at finite momenta. Our results reveal an emergent collective mode of an integrated superconductor–circuit system and establish design principles for engineering or suppressing Cooper plasmons in superconducting terahertz devices and circuits.
Speaker Bio: Alex Potts earned his PhD in 2023 at UC Santa Barbara in the group of Andrea Young. His background and expertise are in femtosecond electronics and the THz dynamics of superconductors. He is now applying ultrafast science on-chip to study the electrodynamics of quantum phases in microstructured cavities.