Low-temperature behavior of aluminium (Al) At a temperature of about 1 K, what is the electrical state of aluminium?

Introduction / Context:
Many pure metals exhibit a transition to a superconducting state at sufficiently low temperature. Aluminium (Al) is a classic example used in low-temperature physics laboratories and cryogenic electronics. This question checks your understanding of the qualitative behavior of aluminium near absolute zero and the concept of a critical temperature for superconductivity.

Given Data / Assumptions:

• Material: high-purity aluminium bulk sample.
• Temperature considered: about 1 K (well below room temperature).
• Magnetic field is negligible, and sample is not carrying large transport currents (so we do not suppress superconductivity).

Concept / Approach:

Superconductivity is characterized by zero DC resistance and the expulsion of magnetic flux (Meissner effect) below a critical temperature Tc. For aluminium, Tc is approximately 1.2 K under zero magnetic field. Thus, at about 1 K (which is below Tc), aluminium is in the superconducting state. Above Tc, it behaves as an ordinary (good) conductor with finite resistivity; it is never an insulator or photoconductor in the usual sense.

Step-by-Step Solution:

Verification / Alternative check:

Transport measurements show a sharp drop of resistivity to instrument noise floor as T passes below Tc. Magnetization measurements show flux exclusion, confirming superconductivity.

Why Other Options Are Wrong:

Conductor: true only above Tc; at 1 K aluminium is more than a mere conductor. Insulator/photoconductor: aluminium is a metal, not a semiconductor; photoconduction is not the governing effect.

Common Pitfalls:

Confusing superconductivity with just “very low resistance” or assuming only alloys become superconducting. Purity and magnetic field do affect Tc slightly, but the qualitative answer remains unchanged.

Final Answer:

superconductor