Bi-directional ultrafast electric-field gating of interlayer transport in a cuprate superconductor
In cuprate superconductors, tunneling between planes makes possible three-dimensional coherent transport. However, the interlayer tunnelling amplitude is reduced when an order-parameter phase gradient between planes is established. As such, c-axis superconductivity can be weakened if a strong electric field is applied along the c axis. We use high-field single-cycle terahertz pulses to gate interlayer coupling in La1.84Sr0.16CuO4. We induce ultrafast oscillations between superconducting and resistive states and switch the plasmon response on and off, without reducing the density of Cooper pairs. Indeed, in-plane superconductivity remains unperturbed throughout, revealing a non-equilibrium state in which the dimensionality of the superconductor is time dependent. The gating frequency is determined by the electric field strength, in the spirit of the ac Josephson effect. Non-dissipative, bi-directional gating of superconductive coupling is of interest for device applications in ultrafast nanoelectronics. It is also a new example of nonlinear terahertz physics, applicable to nanoplasmonics and active metamaterials.