Cooper Pair Breakup in YBCO under Strong Terahertz Fields
  We show that strong electric fields of ~ 30 kV cm^(-1) at terahertz frequencies can significantly weaken the superconducting characteristics of cuprate superconductors. High-power terahertz time-domain spectroscopy (THz-TDS) was used to investigate the in-plane conductivity of YBa2Cu3O7-delta (YBCO) with highly intense single-cycle terahertz pulses. Even though the terahertz photon energy (~ 1.5 meV) was significantly smaller than the energy gap in YBCO (~ 20-30 meV), the optical conductivity was highly sensitive to the field strength of the applied terahertz transients. Possibly, this is due to an ultrafast, field-induced modification of the superconductor's effective coupling function, leading to a massive Cooper pair breakup. The effect was evident for several YBCO thin films on MgO and LSAT substrates. 
Andreas Glossner (1,2), Caihong Zhang (1), Shinya Kikuta (1), Iwao   Kawayama (1), Hironaru Murakami (1), Paul M\"uller (2) ...
cond-mat.supr-con