1. I don’t have too much on these, but they appear in many forms. Claimed are:
* Low voltages at extremely high currents
* High frequency oscillations
* Excitation with magnetic fields, small voltages, or heat.

1. I briefly looked into this sometime ago with the current-to-voltage Op-amp circuit:
   
2. With heat added to junction, circuit became strong detector of local FM station, but died off with cooling.
3. With small positive voltage added in series with constantan lead at X, circuit became detector again, but poorer.