We have developed active metamaterials based on macroscopic quantum effects capable of quickly tuning their electrical and magnetic responses over a wide frequency range. These metamaterials are based on superconducting elements to form low insertion loss, physically and electrically small, highly tunable structures for the next generation rf electronics. The meta-atoms are rf superconducting quantum interference devices (SQUIDs) that incorporate the Josephson effect. RF SQUIDs have an inductance which includes a contribution from the Josephson inductance of the junction. This inductance is strongly tunable with dc and rf magnetic fields and currents. The rf SQUID metamaterial is a richly nonlinear effective medium introducing qualitatively new macroscopic quantum phenomena into the metamaterials community, namely magnetic flux quantization and the Josephson effect. The coherence of the metamaterials is strongly sensitive to the environment and measurement conditions. The metamaterials also display a unique form of transparency whose development can be manipulated through multiple parametric dependences. Further features such as breathers, superradiance, and self-induced transparency, along with entry into the fully quantum limit, will yield qualitatively new metamaterial phenomena.
This work is supported by the NSF-GOALI and OISE Programs through Grant No. ECCS-1158644 and the Center for Nanophysics and Advanced Materials (CNAM).
Despite the numerous advantages of microwave passive devices using high
temperature superconductors, use of all-HTSC microwave devices has been
limited to weak power signal processing due to the limitations in power handung
capabilities of the materials. Moreover, practical applications of the
HTSC microwave devices have been focused on frequencies below 10 GHz.
These technical barriers can be overcome by understanding the detailed high
frequency electrodynamic properties of high temperature superconductors.
Our experiments, carried out on samples with various degrees of quality over
a broad dynamic range of microwave power, frequency, external magnetic
fields and temperatures, suggests that for the improvement of the power handling
capability and an increase of the frequency application range, the devices
made of HTSC materials should have fewer Josephson junctions and increased
materials homogeneity.
Evidence of micron-sized structural inhomogeneities in several high transition temperature (Tc) superconductors is presented. By illuminating samples with high energy, highly collimated x rays produced on a synchrotron wiggler, small changes in the lattice were detected over a spatial scale as small as 10 micrometer. In the YBa2Cu3O7-(delta ) crystals, these changes are interpreted as evidence of variations in the oxygen content and in the Nd2-xCexCuO4-y crystal, as a variation in the cerium content. Each type of inhomogeneity can affect the superconducting properties.
We present a brief description of the role played by the motion of magnetic vortices in the power dependence and non-linearity of high Tc superconductors at rf and microwave frequencies. We then review the current understanding of vortex motion at rf and microwave frequencies, and present broadband (45 MHz - 50 GHz) experimental results which shows a striking crossover in the behavior of the vortex dynamics from a low-frequency interaction- dominated regime, to a high frequency essentially single-particle regime. Finally, we discuss the impact these different regimes of vortex motion have on the design and operation of high Tc rf and microwave devices.
We present a brief review of results on the surface impedance of cuprate superconductors, focusing mainly on YBa2Cu3O7-(delta ) (YBCO) and evidence of d-wave superconductivity in that material. We then discuss our recent results on Ba-K-Bi-O thin films, and the effects of DC electric fields on the surface impedance of YBCO films. A summary of our data on high quality thin films and single crystals of the electron-doped Nd1.85Ce0.15CuO4-(delta ) (NCCO) cuprate superconductor follows. Surprisingly, the measurements on NCCO are consistent with the behavior of an s-wave BCS superconductor, in striking contrast to recent results on YBCO. Finally we discuss some of the interesting potential implications of d-wave superconductivity for microwave applications of the cuprates.
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