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Superconductivity is the state of zero electrical resistance manifested in some metals, alloys, or ceramics when cooled below a specific low temperature known as the "Critical Temperature" or Tc. Below Tc, the material also expels an applied magnetic field from its interior. This is known as the Meissner Effect.
Heike Kamerlingh Onnes discovered superconductivity in 1911. Since its discovery, scientists have recognized its vast potential for industrial applications due to its signature ability to transport electrical current without resistance. Thanks to this, nowadays, we can create the superconducting magnets needed in magnetic resonance imaging and for particle accelerators. The Meissner effect has also inspired the creation of prototypes for magnetically levitated trains for future transportation without friction.
A Josephson junction is the device created when two superconducting materials are brought in close contact through a thin insulator, or a "weak link" . The drawing shows an example of an Insulating Type Josephson junction. If a constant voltage (V0) is applied across the junction, an oscillating current will appear capable of radiating electromagnetic signals. The frequency of oscillation of this current is given by (2e/h)*V0 ≈ (0.5THz/mV)*V0, where "e" is the charge of the electron, and "h" is Planck's constant. This behavior is known as the "ac Josephson Effect." If, on the other hand, a Josephson junction is exposed to an electromagnetic signal of fixed frequency (f), a dc voltage will appear across the junction. Therefore, Josephson junctions are natural frequency-to-voltage transducers with a conversion factor of approximately half a terahertz per millivolt. The ac Josephson Effect has stimulated a significant volume of research targeted at developing sources, , and detectors in the THz range. The utilization of this effect in applications, however, has been limited because of the small amount of power that can be delivered by or coupled to individual Josephson junctions. At NanoJunctions, we are investigating ways to increase the power that can be coupled or produced by our Josephson Weak Links for applications.
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 For low-temperature superconductors, twice the gap energy is on the order of 3meV. For high-temperature superconductors, it could be as high as 60meV
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