2 research outputs found
Generalized Josephson plasmons in bilayer superconductors
Layered superconductors like High-Tc cuprates display out-of-plane plasma
oscillations between layers sustained by the weak Josephson coupling among the
superconducting sheets, the so-called Josephson plasmons. Bilayer cuprates
hosts two of such modes, but due to the anisotropy of the electronic response
their description at generic wavevector cannot be separated from that of the
in-plane oscillations. In this paper we provide an analytical theoretical
framework able to describe the dispersions and the polarizations of the
generalized plasma modes of such systems, that has been only partly addressed
by previous work in the literature. We then employ it to explain the peculiar
characteristics of their linear optical response, by providing a fully
microscopic explanation for the appearance of a finite-frequency peak in the
real part of the optical conductivity. On a wider perspective, the complete
characterization of the Josephson plasma modes provided by our approach
represents a groundwork to address open issues raised by recent experiments
with strong THz pulses, able to drive them beyond the linear-response regime.Comment: 21 pages, 8 figure
Manipulating Plasma Excitations with Terahertz Light Pulses in Superconducting Cuprates
Layered cuprates offer a preferential playground for optical non-linearity
thanks to the emergence, below Tc, of soft out-of-plane Josephson plasmons. The
hallmark of such a non-linearity is the observation of Third Harmonic
Generation, that has been theoretically understood as a sum-frequency process
involving a two-plasmon excitation. However, recent experiments in cuprates
with two planes per unit cell challenge this interpretation, due to the lack of
resonant response at the temperature where the driving frequency matches the
plasma energy scale, as observed instead in single-layer cuprates. Here we show
that such an apparent discrepancy in bilayer systems can be resolved by taking
into account the combined effect of light polarization and Josephson-coupling
anisotropy on setting the energy range where three-dimensional layered plasma
modes can be resonantly excited. Our results offer a novel perspective on the
possibility to tune on demand high-harmonic generation by artificially
designing Josephson heterostructures