Two-fluid dynamics in driven YBa2Cu3O6.48

Coherent optical excitation of certain phonon modes in YBa2Cu3O6+x has been shown to induce superconducting-like interlayer coherence at temperatures higher than Tc. Recent work has associated these phenomena to a parametric excitation and amplification of Josephson plasma polaritons, which are overdamped above Tc but are made coherent by the phonon drive. However, the dissipative response of uncondensed quasiparticles, which do not couple in the same way to the phonon drive, has not been addressed. Here, we investigate both the enhancement of the superfluid density, co sigma 2(co), and the dissipative response of quasiparticles, sigma 1(co), by systematically tuning the duration and energy of the mid-infrared pulse while keeping the peak field fixed. We find that the photoinduced superfluid density saturates to the zero-temperature equilibrium value for pulses made longer than the phonon dephasing time, while the dissipative component continues to grow with increasing pulse duration. We show that superfluid and dissipation remain uncoupled as long as the drive is on, and identify an optimal regime of pump pulse durations for which the superconducting response is maximum and dissipation is minimized.

Automated summary

By exciting certain phonon modes in YBa2Cu3O6+x, superconducting-like interlayer coherence can be induced at temperatures higher than Tc. Recent research has linked these phenomena to a parametric excitation and amplification of Josephson plasma polaritons, which are overdamped but made coherent by the phonon drive. However, the dissipative response of uncondensed quasiparticles, which do not couple in the same way to the phonon drive, has not been studied. In this study, we investigate the enhancement of superfluid density and the dissipative response of quasiparticles by systematically tuning the duration and energy of the mid-infrared pulse, while keeping the peak field fixed. We find that the photoinduced superfluid density saturates to the equilibrium value for pulses longer than the phonon dephasing time, while the dissipative component continues to grow with increasing pulse duration. We show that superfluid and dissipation remain uncoupled as long as the drive is on, and identify an optimal regime of pump pulse durations for maximum superconducting response and minimized dissipation.