Phase dynamics in a stack of inductively coupled intrinsic Josephson junctions and terahertz electromagnetic radiation

Abstract

The Josephson effect is a phenomenon of current flow across two weakly linked superconductors separated by a thin barrier, i.e. Josephson junction, associated with coherent quantum tunneling of Cooper pairs. Many novel phenomena appear due to the nonlinear property of the Josephson effect, such as Shapiro steps in dc current-voltage (IV) characteristics of a Josephson junction under microwave shining, which can be used as a voltage standard. The Josephson effect also provides a unique way to generate high-frequency electromagnetic (EM) radiation by dc bias voltage as the inverse process of the Shapiro step. The discovery of cuprate high-T c superconductors accelerated the effort to develop novel source of EM waves based on a stack of atomically dense-packed intrinsic Josephson junctions (IJJs), since the large superconductivity gap covers the whole terahertz (THz) frequency band. Very recently, strong and coherent THz radiations have been successfully generated from a mesa structure of Bi 2 Sr 2 CaCu 2 O 8+ single crystal which works both as the source of energy gain and as the cavity for resonance. This experimental breakthrough posed a challenge to theoretical study on the phase dynamics of stacked IJJs, since the phenomenon cannot be explained by the known solutions of the sine-Gordon equation so far. It is then found theoretically that, due to huge inductive coupling of IJJs produced by the nanometer junction separation and the large London penetration depth of order of m  of the material, a novel dynamic state is stabilized in the coupled sine-Gordon system, in which   kinks in phase differences are developed responding to the standing wave of Josephson plasma and are stacked alternately in the c -axis.This novel solution of the inductively coupled sine-Gordon equations captures the important features of experimental observations. The theory predicts an optimal radiation power larger than the one observed in recent experiments by orders of magnitude, and thus suggests the technological relevance of the phenomena.

Superluminal geometrical resonances observed inBi2Sr2CaCu2O8+xKatterwe1, Rydh2, Motzkau3 et al. 2010Phys. Rev. B373640View full textAdd to dashboardCite

“…Therefore, IJJs are intensively studied as possible candidates for realization of a coherent THz oscillator. 7,[12][13][14][15][16][17][18][19][20][21][22][23][24][25] The flux-flow oscillator (FFO) is based on regular motion of Josephson vortices (fluxons). 26 To facilitate coherent emission from a stacked FFO, fluxons in the stack must be arranged in a rectangular (in-phase) lattice.…”

Optical excitation of Josephson plasma solitons in a cuprate superconductor

“…From the Josephson equations, the phase ϕ z (x, y, t ) advances in time as ϕ z (x,y,t ) ∝ E(x,y,t ) dt and acts back onto the inductive coupling as L J (x,y,t ) ∝ 1/cos ϕ z (x,y,t ). The resulting electrodynamics is well captured by the sine-Gordon equation 17 , which in one dimension and in the absence of dissipation readsIn this equation ε r is the dielectric permittivity of the insulating layers, c is the speed of light in vacuum and λ J is the Josephson penetration depth. For small electric fields and thus small phase, we have sin ϕ z (x,t ) ∼ ϕ z (x,t ) and the sine-Gordon equation yields a linear wave equation, leading to Josephson plasma waves.…”

Effect of ordered array of magnetic dots on the dynamics of Josephson vortices in stacked SNS Josephson junctions under DC and AC current

“…This is, e.g., motivated by its potential to use such Josephson systems for creating high-frequency electromagnetic oscillations (see Refs. [14,15] for review). However, to increase the intensity of such sub-terahertz electromagnetic radiation sources, Josephson oscillations have to be in phase in the different junctions.…”