Powerful Terahertz Emission from a Bi2Sr2CaCu2O8+delta Mesa Operating Above 77 K

Mesa-shaped structures of the high critical temperature (high-T-c) superconductor Bi2Sr2CaCu2O8+delta; contain stacked intrinsic Josephson junctions. As such, they are a promising source of coherent radiation in the "terahertz gap" range, spanning from approximately 0.3 to 2.0 THz. Technological applications of these devices become far more practical if they can be operated at a cryogenic bath temperature of 77 K or higher. Previous works have reported emission from this type of device at high terahertz power levels at lower operating temperatures, 40-60 K, while at T-bath >= 77 K observed power levels have gen-erally been low. Here we report generation of 130 mu W of coherent power at 0.456 THz from a mesa of Bi2Sr2CaCu2O8+delta; doped with 0.16 holes per Cu atom, at a bath temperature of 77.4 K. We find that the device radiates terahertz power when clearly identifiable cavity modes are excited, and that the frequency and bias voltage corresponding to each of these modes is almost independent of temperature. This is con-sistent with these modes having terahertz-frequency electric fields with very little dependence on vertical position within the mesa. We also find that the terahertz power radiated from any given mode decreases monotonically as the mesa temperature is increased. On the other hand, the low-frequency modes become inaccessible at low temperatures due to retrapping of the intrinsic Josephson junctions, and the maximum radiation power for the emitting mode is typically achieved at the temperature at which the retrapping voltage reaches the resonance voltage for this mode.