The Transition into the Intermediate State of Hollow Superconducting Cylinders

The transition from the superconducting to the intermediate state has been investigated for hollow tin cylinders with various ratios of inner to outer radii. Thermodynamic arguments show that for values of this ratio greater than ($\frac{2^{\frac{1}{2}}}{2}$) the free energy in the normal state becomes less than that in the superconducting state at applied fields less than one half the critical field. The experimental results indeed show that for ratios of inner to outer radii greater than ($\frac{2^{\frac{1}{2}}}{2}$) the intermediate state begins to appear at less than one-half the critical field, whereas for smaller ratios the intermediate field appears at one-half the critical field.