Superconductors are materials that can conduct electricity with zero resistance; this means that electrons move freely without losing any of their energy whatsoever.
Many elements can become superconducting at very low temperatures, e.g. Tin (Sn), Mercury (Hg), Lead (Pb), Aluminum (Al), Zinc (Zn), etc. However, more interesting for technological applications are some Copper (Cu) or Lead (Pb) compounds.