[hamdani yusuf (OP)]

Is electrical conductance of superconductor affected by frequency of the voltage?
Some sources say that superconductors have zero resistance up to some limit of current density. But I think the test used DC or low frequency AC voltage. Most of superconductor pictures/video shows that they are not shiny, hence I infer that they can't conduct electricity very well in the frequency range of visible light.
Do they still have zero resistance in higher frequency? Does anyone have reference to this kind of experiment?

[evan_au]

Superconductors are able to carry DC at much higher current densities than AC.
- Superconducting power lines carry DC rather than 50Hz or 60Hz AC
- Current high-temperature superconductors are all Type II, and are not suitable for high-frequency applications

One application that uses superconductors as a transmission line for microwaves (up to 3GHz) is in particle accelerators.
- They typically use niobium metal, which is a Type I superconductor
- with superfluid helium cooling
- In this application, the microwaves don't travel through the bulk metal, but through the vacuum inside a niobium-plated superconducting tube.
- In operation, the equipment has to screen out the Earth's magnetic field, as the Earth's DC magnetic field increases AC losses

One way to view the nature of the BCS RF resistance is that the superconducting Cooper pairs, which have zero resistance for DC current, have finite mass and momentum which has to alternate sinusoidally for the AC currents of RF fields, thus giving rise to a small energy loss.

See: https://en.wikipedia.org/wiki/Superconducting_radio_frequency#Physics_of_SRF_cavities

[hamdani yusuf (OP)]

The amount of loss in an SRF resonant cavity is so minute that it is often explained with the following comparison: Galileo Galilei (1564–1642) was one of the first investigators of pendulous motion, a simple form of mechanical resonance. Had Galileo experimented with a 1 Hz resonator with a quality factor Q typical of today's SRF cavities and left it swinging in an entombed lab since the early 17th century, that pendulum would still be swinging today with about half of its original amplitude.

https://en.wikipedia.org/wiki/Superconducting_radio_frequency#Introduction
This description shows that the energy loss is not exactly 0.