Question

Carbon nanotube shows magneto-resistive effects:

• A. at high temperature
• B. at low temperature
• C. at room temperature
• D. at very high temperature

Hint:

As a general rule in condensed matter physics, most quantum coherence effects (like the Aharonov-Bohm effect, quantum Hall effect, superconductivity) are best observed, or only observable, at very low temperatures.

Answer 1

The Correct Option is B

Step 1: Concept Overview:
Magnetoresistance is a material's ability to alter its electrical resistance when exposed to a magnetic field. In carbon nanotubes (CNTs), this effect arises mainly from quantum mechanics, like the Aharonov-Bohm effect.
Step 2: In-Depth Explanation:
Magnetoresistance in CNTs stems from quantum interference. Observation of these effects requires electrons to maintain quantum coherence while traversing the material.
Elevated temperatures increase thermal energy, causing substantial lattice vibrations (phonons). Frequent and strong collisions between electrons and phonons (electron-phonon scattering) disrupt the phase coherence of the electron wave function.
Consequently, observing quantum magnetoresistance necessitates minimizing thermal scattering by cooling the material to very low temperatures. At these temperatures, electron coherence lasts longer, enhancing quantum interference effects.
Step 3: Conclusion:
Magnetoresistance in carbon nanotubes is a quantum phenomenon observable primarily at low temperatures where thermal scattering is minimal.