Non-linear Terahertz Driving of Plasma Waves in Layered Cuprates

TL;DR

This paper demonstrates that intense THz pulses can non-linearly excite both out-of-plane and in-plane plasma modes in layered cuprate superconductors through a two-plasmon mechanism, revealing new control possibilities over phase stiffness.

Contribution

It uncovers the ability to drive in-plane plasma modes with THz pulses via a two-plasmon process, challenging previous assumptions of insensitivity and linking it to phase fluctuations.

Findings

THz pulses can excite in-plane plasma modes in cuprates.

The in-plane response persists above the critical temperature.

Differences in thermal effects are due to anisotropic Josephson couplings.

Abstract

The hallmark of superconductivity is the rigidity of the quantum-mechanical phase of electrons, responsible for superfluid behavior and Meissner effect. The strength of the phase stiffness is set by the Josephson coupling, which is strongly anisotropic in layered superconducting cuprates. So far, THz light pulses have been efficiently used to achieve non-linear control of the out-of-plane Josephson plasma mode, whose frequency scale lies in the THz range. However, the high-energy in-plane plasma mode has been assumed to be insensitive to THz pumping. Here, we show that THz driving of both low-frequency and high-frequency plasma waves is possible via a general two-plasmon excitation mechanism. The anisotropy of the Josephson couplings leads to marked differences in the thermal effects among the out-of-plane and in-plane response, consistently with the experiments. Our results link the observed survival of the in-plane THz non-linear driving above $T_c$ to enhanced fluctuating effects in the phase stiffness in cuprates, paving the way to THz impulsive control of phase rigidity in unconventional superconductors.