C. Watanabe

Continuous 30 μW terahertz source by a high-Tc superconductor mesa structure

Using a modified mesa structure of high-Tc superconducting Bi2Sr2CaCu2O8+δ with a thin underlaying base superconductor (∼3u2009μm), the effective working temperature of the continuous and monochromatic terahertz emitter is extended up to 70u2009K, and the maximum power of ∼30u2009μW at 0.44 THz is achieved at the relatively high temperature of Tbu2009=u200955u2009K in a low bias current retrapping region. The diverging behavior of the intensity occurring at 55u2009K in the low current regime without hot spot formation may provide us an important clue for the stronger THz radiation from intrinsic Josephson junction devices.

Direct imaging of hot spots in Bi2Sr2CaCu2O8+δ mesa terahertz sources

Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612nm fluorescence line of Eu^{3+} in a europium chelate. The images directly reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.

Thermoreflectance microscopy measurements of the Joule heating characteristics of high- Tc superconducting terahertz emitters

Joule heating is the central issue in order to develop high-power and high-performance terahertz (THz) emission from mesa devices employing the intrinsic Josephson junctions in a layered high transition-temperature Tc superconductor. Here, we describe a convenient local thermal measurement technique using charge-coupled-device-based thermoreflectance microscopy, with the highest spatial resolution to date. This technique clearly proves that the relative temperature changes of the mesa devices between different bias points on the current-voltage characteristics can be measured very sensitively. In addition, the heating characteristics on the surface of the mesa devices can be detected more directly without any special treatment of the mesa surface such as previous coatings with SiC micro-powders. The results shown here clearly indicate that the contact resistance strongly affects the formation of an inhomogeneous temperature distribution on the mesa structures. Since the temperature and sample dependencies...

Direct Imaging of Hot Spots in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+delta} Mesa Terahertz Sources

Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612nm fluorescence line of Eu^{3+} in a europium chelate. The images directly reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.