Superconductivity

Why in News?

• Physicists at the University of L’Aquila in Italy have recently made a breakthrough by achieving a full microscopic understanding of the superconductivity of Mercury for the first time.

Highlights

• Superconductivity was first discovered in mercury, yet scientists required 111 years to explain how it becomes superconducting.
• Superconductivity refers to a state when a material can conduct electricity without any resistance. It is observed in many materials when they are cooled below a critical temperature.
• In BCS (Bardeen-Cooper-Schrieffer) superconductors, vibrational energy released by the grid of atoms encourages electrons to pair up, forming so-called Cooper pairs.
• These Copper pairs can move like water in a stream, facing no resistance to their flow, below a threshold temperature.
• These could explain why mercury has such a low threshold temperature (around –270°C).
• Spin-orbit coupling (SOC) is the way an electron’s energy is affected by the relationship between its spin and its momentum.
• SOC gave a better view of the phonons’ energies and explain why mercury has such a low threshold temperature (approx. –270º C).
• Another factor was the Coulomb repulsion (a.k.a. ‘like charges repel’) between two electrons in each pair.
• The superconducting state is determined by a balance between an attractive interaction between electrons, mediated by phonons, and the repulsive Coulomb interaction (electrostatic repulsion between negative charges).