# How fast can you 'switch' between superconducting and normal modes?

1. Dec 3, 2012

### VortexLattice

The title, basically. If we're at a temperature below the critical temperature (let's just say for a Type 1 superconductor) and an applied magnetic field less than the critical magnetic field, it will be in the superconducting state.

But if we increase the field beyond the critical point, it will go into the normal state. So if we set the temperature well below $T_c$ and made the applied field right below $H_c$, it seems like we could oscillate $H$ to make it go in and out of the superconducting state. Is this the case, first of all?

Second, if that's not somehow impossible, I imagine there must be some sort of upper limit to the frequency you could do this at. You can get pretty damn fast magnetic field oscillations. Will the superconductor switches states back and forth that fast?

2. Dec 3, 2012

### f95toli

Look up some papers (and there are many) on transition edge detectors.
These are often used for radio astronomy, and are based upon the principle you describe (but with temperature, not B-field).

3. Dec 3, 2012

### christopher.s

This paper1 describes an ideal integrating bolometer using a superconducting strip of aluminum as a heat switch. They apply a magnetic field by the application of current through niobium leads which effectively switches the aluminum leads between their superconducting and non-superconducting state. I don't know how fast the limit is, but they state their sampling rate is 2khz for the detector, so it is at least that fast! That is an awesome question, I imagine it is limited by the inductance of the coil or something. I don't understand what is happening well enough to know.

1 - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040074297_2004071214.pdf