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Benjamin Franklin

Prof. Timothy Benseman

Stacks of intrinsic Josephson junctions (IJJs) in extremely anisotropic high-temperature superconductors such as Bi2Sr2CaCu2O8 are a promising compact solid-state source of coherent radiation in the 'terahertz gap' range. At present, no such sources exist in the range from approximately 0.5 THz to 1.3 terahertz, and this region is of particular interest for many applications in science, medicine, and high-bandwidth communications, as well as in security and defense. In order to generate technologically useful levels of power from these stacks, it is necessary to obtain efficient phase-synchronized emission from the largest possible number of individual Josephson junctions. Following this approach, I have recently increased the coherent power output from this type of device to 0.6 milliwatts at 0.51 THz, which is approximately the power level required for practical real-time imaging applications.

High temperature superconductors which contain stacked IJJs - namely the bismuth- and thallium-based cuprate compounds - offer a further unique property: they are expected to allow the propagation of Josephson Plasma Waves. Theorists predict that the copper-oxide planes of these HTS cuprates act as natural superconducting waveguides which can channel energy through the structures of these crystals at microwave and terahertz frequencies. My experiments in Bi2Sr2CaCu2O8 provide strong indirect evidence of this phenomenon. The efficient propagation and non-linearity of Josephson Plasma Waves offers the possibility of novel devices for THz frequency signal processing, such as ridge waveguides, mixers, and modulators/demodulators. Such devices would be extremely valuable for ultra-high bandwidth telecommunications for both wired and wireless applications.

Realizing the full technological potential of complex oxide materials such as these will require advances in thin film growth technology beyond what is presently available, and I am currently developing techniques for growth of thin films with the quality of a single crystal.