 It reflects the general fact that it is the fluxoid rather than the flux which is quantized in superconductors.The Little-Parks effect demonstrates that the vector potential couples to an observable physical quantity, namely the superconducting critical temperature.Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated.