Cooper pairs

Definition

Cooper pairs are pairs of electrons that are bound together at low temperatures in a superconductor, allowing them to move without resistance. This phenomenon is a fundamental aspect of superconductivity, where these paired electrons form a collective ground state that enables the flow of electric current without energy loss. The concept of Cooper pairs was introduced by Leon Cooper in 1956 and is crucial for understanding the behavior of superconducting materials.

5 Must Know Facts For Your Next Test

1. Cooper pairs arise due to an attractive interaction between electrons, typically mediated by lattice vibrations called phonons in a superconductor.
2. The formation of Cooper pairs leads to a condensation into a collective ground state, which is essential for the onset of superconductivity.
3. In a Cooper pair, the two electrons have opposite spins and momenta, allowing them to overcome their natural repulsion and pair up.
4. Cooper pairs can exist over long distances and are responsible for the coherence properties observed in superconductors.
5. The breaking of Cooper pairs under external perturbations leads to the loss of superconductivity, demonstrating their role as key players in the superconducting phase.

Review Questions

• How do Cooper pairs contribute to the phenomenon of superconductivity?
  • Cooper pairs contribute to superconductivity by allowing electrons to form bound states that can move through a lattice without scattering off impurities or defects. This occurs because the attractive interaction between electrons allows them to overcome their natural repulsion, forming pairs that act collectively. As a result, these paired electrons can condense into a lower energy state, enabling a continuous flow of electric current without resistance.
• Discuss the role of phonons in the formation of Cooper pairs and how this relates to BCS theory.
  • Phonons play a significant role in the formation of Cooper pairs as they mediate the attractive interaction between electrons. In Bardeen-Cooper-Schrieffer (BCS) theory, this interaction is crucial for pairing electrons with opposite momentum and spin. The theory explains that when an electron moves through the lattice, it disturbs its surroundings, creating a phonon that can attract another electron into a Cooper pair. This mechanism highlights how lattice vibrations facilitate the emergence of superconductivity.
• Evaluate the impact of temperature on Cooper pair formation and its implications for superconducting behavior.
  • Temperature has a critical impact on Cooper pair formation; as temperature decreases, thermal fluctuations diminish, allowing pairs to form more easily and persist longer. This relationship is central to understanding why superconductivity occurs at low temperatures. When the temperature rises above a certain critical value, thermal energy disrupts the pairing mechanism, leading to the breaking of Cooper pairs and loss of superconducting properties. Thus, the temperature dependence of Cooper pair stability is fundamental for determining superconducting transitions in materials.

Related terms

Superconductivity: A state of matter characterized by the complete absence of electrical resistance and the expulsion of magnetic fields occurring in certain materials at low temperatures.

Bardeen-Cooper-Schrieffer (BCS) Theory: A theoretical framework developed to explain superconductivity, detailing how Cooper pairs form and interact to create the superconducting state.

Fermions: A class of particles, including electrons, that follow the Pauli exclusion principle, which states that no two identical fermions can occupy the same quantum state simultaneously.