From Academic Kids
Despite its name, high-temperature superconductivity still occurs at cryogenic temperatures. The main difference from low-temperature superconductivity is usually that 'high-Tc' superconductors can use liquid nitrogen (at 77 K) as a coolant while low-temperature superconductors always need liquid helium (4.2 K) temperatures and below.
All known high-Tc superconductors are so-called Type-II superconductors. A Type-II superconductor allows magnetic field to penerate its interior in the units of flux quanta, creating 'holes' (or tubes) of normal metallic regions in the superconducting bulk. This property makes high-Tc superconductors capable of sustaining much higher magnetic fields.