Three-Dimensional Simulations of the Electrothermal and Terahertz Emission Properties ofBi2Sr2CaCu2

Abstract

We used 2D coupled sine-Gordon equations combined with 3D heat diffusion equations to numerically investigate the thermal and electromagnetic properties of a 250 × 70 µm 2 intrinsic Josephson junction stack. The 700 junctions are grouped to 20 segments; we assume that in a segment all junctions behave identically. At large input power a hot spot forms in the stack. Resonant electromagnetic modes, oscillating either along the length ((0, n) modes) or the width ((m, 0) modes) of the stack or having a more complex structure, can be excited both with and without a hot spot. At fixed bath temperature and bias current several cavity modes can coexist in the absence of a magnetic field. The (1, 0) mode, considered to be the most favorable mode for THz emission, can be stabilized by applying a small magnetic field along the length of the stack. A strong field-induced enhancement of the emission power is also found in experiment, for an applied field around 5.9 mT.

Compact High- Tc Superconducting Terahertz emitter operating up to 86 K

“…For this bias point, Fig. 5(b) shows a map of the power density q (x, y) dissipated by in-plane currents in the stack, averaged over time and the z direction and given in the unit Regions of high dissipation in this type of plot coincide with regions where columns (in the z direction) of fluxons and antifluxons have formed in the stack [60,61]. This means that for the pattern in Fig.…”

“…To obtain more insight into the electrothermal behavior of the stack, particularly in view of high-temperature operation and in view of resonant modes, we simulate a 200 × 200 μm 2 stand-alone 600-junction stack with a critical current density j c = 2 kA/cm 2 using three-dimensional coupled sine-Gordon equations as in Ref. [61]. Some results are shown in Fig.…”

“…The low value of the observed switching current may arise from the nucleation of some Josephson vortices, immediately switching the whole stack into its resistive state. Such a scenario is not unrealistic, since our stack is much larger than the Josephson length, which is about 0.3 μm for j c = 2 kA/cm 2 [60,61].…”

“…The basic model is described in Refs. [60,61]. Here we give a short summary, with a focus on changes relative to the model discussed in Ref.…”

“…Here we give a short summary, with a focus on changes relative to the model discussed in Ref. [61]. The electrical and thermal model parameters depend on temperature, and thus, for an inhomogeneous temperature distribution, on x, y, and z.…”