Geometrical Resonance Conditions for THz Radiation from the Intrinsic Josephson Junctions in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathbf{O}}_{8+\delta }$

Subterahertz radiation emitted from a variety of short rectangular-, square-, and disk-shaped mesas of intrinsic Josephson junctions fabricated from a ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ single crystal was studied from the observed $I\mathrm{\text{−}}V$ characteristics, far-infrared spectra, and spatial radiation patterns. In all cases, the radiation frequency satisfies the conditions both for the ac Josephson effect and for a mesa cavity resonance mode. The integer higher harmonics observed in all spectra imply that the ac Josephson effect plays the dominant role in the novel dual-source radiation mechanism.

Figure 1

(a) Sketch of a cylindrical disk IJJ mesa. The grazing angle forming the groove of $10\mu \mathrm{m}$ width is approximately 5°. (b) Scanning ion microscope images of a rectangular (left), square (center), and disk (right) mesa.

Figure 2

(a) The $I\mathrm{\text{−}}V$ characteristics (left scale) and output radiation intensity detected by the Si bolometer (right scale) from disk mesa $D3$ at the bath temperature $T=25.0\mathrm{K}$ of its maximal radiation intensity are shown. The inset shows the $c$-axis $R\mathrm{\text{−}}T$ curve. (b) Details of the shaded high bias region in Fig. 2a where the emission is observed.

Figure 3

(a) The radiation spectra measured by the FTIR spectrometer for three disk mesas. The inset shows the observed frequencies versus $1/(2a)$. The error bars reflect the trapezoidal cross-section profile. The dashed line represents the resonance frequency expected from the cylindrical cavity TM (1, 1) mode with $ϵ=17.6$. (b) Polar plot of the radiation intensity for disk mesa $D3$. Three different symbols correspond to three different runs. The solid orange and dashed black curves are the best fits to the dual-source model and its cavity component, respectively.

Figure 4

The radiation spectra for the square (S1) and rectangular (R1) mesas. The inset shows the observed frequencies versus the narrower width inverse $1/w$, where the circles are previous data [7]. The black dashed line represents the resonance frequency expected for the rectangular cavity TM (0, 1) mode with $ϵ=17.6$.