Non-thermal response of YBCO thin films to picosecond THz pulses

TL;DR

This study investigates the non-thermal ultrafast photoresponse of YBCO thin films to picosecond THz pulses, revealing a vortex rearrangement mechanism distinct from thermal effects, with implications for high-speed superconducting devices.

Contribution

It provides the first detailed analysis of YBCO thin film responses to picosecond THz pulses, highlighting a non-thermal vortex dynamics mechanism not explained by traditional models.

Findings

Optical responses fit the two-temperature model with fast and slow components.

THz responses show no bolometric component and larger amplitudes than predicted.

High-frequency currents induce vortex rearrangement in the superconductor.

Abstract

The photoresponse of YBa2Cu3O7-d thin film microbridges with thicknesses between 15 and 50 nm was studied in the optical and terahertz frequency range. The voltage transients in response to short radiation pulses were recorded in real time with a resolution of a few tens of picoseconds. The bridges were excited by either femtosecond pulses at a wavelength of 0.8 \mu m or broadband (0.1 - 1.5 THz) picosecond pulses of coherent synchrotron radiation. The transients in response to optical radiation are qualitatively well explained in the framework of the two-temperature model with a fast component in the picosecond range and a bolometric nanosecond component whose decay time depends on the film thickness. The transients in the THz regime showed no bolometric component and had amplitudes up to three orders of magnitude larger than the two-temperature model predicts. Additionally THz-field dependent transients in the absence of DC bias were observed. We attribute the response in the THz regime to a rearrangement of vortices caused by high-frequency currents.