Step 1: Understanding the Question:
The question identifies a class of materials that can conduct electricity without any energy loss when cooled below a specific critical temperature.
Step 2: Detailed Explanation:
Superconductors: These are materials that exhibit zero electrical resistance and the expulsion of magnetic fields (Meissner effect) when cooled below a characteristic critical temperature ($T_c$).
In a superconductor, electrons form "Cooper pairs" that move through the lattice without scattering off atoms, which is the cause of resistance in normal conductors.
This allows a current to flow indefinitely in a closed loop without an external power source.
Analysis of other options:
Conductors: Like Copper or Silver, they have low resistance but never zero at ordinary temperatures. They always lose some energy as heat.
Semiconductors: Have moderate resistance that depends heavily on doping and temperature.
Insulators: Have extremely high resistance and do not allow the flow of current under normal conditions.
Step 3: Final Answer:
Super conductors are the materials that possess zero electrical resistance.