Plasmon nanogap-enhanced transition temperature of terahertz active device based on superconductors

Abstract

We present terahertz optical properties of GdBa2Cu3O7-x (GdBCO) superconducting thin films. GdBCO films with a thickness of about 105 nm were grown on a LaAlO3 (LAO) single crystal substrate using a conventional pulsed laser deposition (PLD) technique. Using an Ar ion milling system, the thickness of the GdBCO film was reduced to 58 nm, and its surface was also smoothened. Terahertz (THz) transmission spectra through two different GdBCO films are measured over the range between 0.2 and 1.5 THz using THz time domain spectroscopy. Interestingly, the THz transmission of the thinner GdBCO film has been increased to six times larger than that of the thicker one, while the thinner film is still maintaining its superconducting property at below 90 K. Those thinner superconducting films are suitable to develop various THz applications combined with plasmonic nanostructures to enhance light-matter interactions. Furthermore, this combined system would create opportunities in studying electrodynamics of Cooper pairs inside the limited volume underneath the plasmonic structures and enhancing a transition temperature of the active terahertz switching device based on the superconducting thin films.