Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-<i>T</i><sub>c</sub>superconductor Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8 +<b><i>δ</i></b></sub>
Journal of physics. Condensed matter